Blog search results for Tag: Horticulture

Agrifood

As we speak, apples and pears are ripening on the trees. But how do you grow apple and pear trees from scratch and keep them alive? Our resident gardening expert, Professor Geoff Dixon, investigates.

Autumn is the ‘season of mists and mellow fruitfulness’, as John Keats said in his Ode to Autumn. It is a time for harvesting temperate tree fruits, especially apples and pears in gardens and orchards.

This fruit is distinctive and delicious. The ‘Sunset’ apple cultivar, derived from the Cox’s Orange Pippin, produces red and gold striped fruit and sweet tasting flesh, while the French pear cultivar doyenne du comice has the most superb taste if caught at peak ripeness.

The sunset apple<
The sunset apple.

Both apples and pears ripen after harvesting, emitting ethylene and passing through a climacteric, or critical biological stage. When respiration reaches a peak, the fruits’ flavour is most satisfying.

Both apples and pears are best planted in late autumn or during winter when the trees are dormant, either as container-grown or preferably bare root trees. Place each tree in a hole that is large enough for the entire root system, ensuring that the graft union sits well above the soil level.

Each tree consists of two parts: the rootstock, selected originally from wild species, and the scion, which is the fruiting cultivar. Apple cultivars mostly dwarf Malling no. 9, and pear scions are grafted onto quince rootstocks. A stake should be driven into the hole before putting the tree in place.

Pour ample water into the hole, keeping the roots wet. Do so again once soil is replaced and firmed round the tree. As the tree establishes and produces leaves and flowers, water well and regularly, especially during dry periods.

French pear cultivar doyenne du comice
French pear cultivar doyenne du comice

Feed with fertilisers that contain large amounts of potash and phosphate but minimal nitrogen. This encourages vigorous root growth. Sprinkling compost or farmyard manure around the tree helps retain soil moisture.

Climate change is having significant deleterious impacts on all members of the Rosaceae family, including apples and pears. Australian studies indicate that temperatures are reaching higher than the evolutionary maximum for these species.

This stresses the plants. It adversely affects their health and performance and reduces their ability to store carbon and produce fruit crops.

The Pear scab Venturia pirina
The pear scab Venturia pirina

Levels of pest and disease infections are increasing. In particular, sap-sucking woolly aphids (Eriosoma lanigerum) have increased from minor to major apple pests in the last decade. Pear scab Venturia pirina has become a major cause of defoliation.

Chemical control options for both are limited, but regular drenching sprays with seaweed extracts may reduce their impact. Seaweed extracts additionally provide some foliar absorbed nutrients and increase the visual quality of fruit.


Professor Geoff Dixon is author of Garden practices and their science, published by Routledge 2019.

Agrifood

Which species can you plant to increase the nutrients in your soil and boost biodiversity, and which pathogen tackles some of those pesky weeds? Our resident gardening expert, Professor Geoff Dixon, tells us more.

The term ‘sustainability’ for gardening means replacing what you take out of the soil and supporting localised biodiversity. Harvested crops, for example, take out nutrients and water from the soil. Replacements should be supplied that aid biodiversity and have minimal impact, or zero impact, on climate change.

Seaweed (Ascophyllum) has been recognised as a valuable fertiliser source in British coastal areas for centuries. Now, proprietary seaweed extracts are gaining popularity either when applied directly as liquid feeds or sprays, or when added into composts.

Classed as biostimulants, seaweed extracts contain several micro-nutrients and a range of valuable plant stimulatory growth regulators. They encourage pest and disease tolerance, increase frost tolerance, stimulate germination, increase robust growth, and add polish to fruit such as apples and pears.

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Seaweed bolsters some of the nutrients lost through gardening. Image from Geoff Dixon.

Benefits of borage

Some plants are very effective supporters of biodiversity. Borage (Borago officinalis), known also as starflower or bugloss, is a robust annual plant of Mediterranean origin with pollinator-attractive blue flowers.

It is very drought resistant and suitable for dry gardens. Although an annual, it is self-seeding and could spread widely. It is very attractive to bees as it produces copious light – and delicately flavoured honey.

Its flowers and foliage are edible with a cucumber-like flavour, making it suitable in salads and as garnishes, while in Germany it is served as grűne soße (green sauce). When used as a companion plant for crops such as legumes or brassicas, it will also help to suppress weeds.

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Borage is good for bee and belly. Image from Geoff Dixon.

Weeding out the problem

Weeds are a continuous problem for gardeners and their prevalence varies with the seasons. Groundsel (Senecio vulgaris), also known as ‘old man in the spring’, persists whatever the weather.

It is ephemeral but can seed and regrow several times per year. As a result, once established, it is difficult to control without very diligent hand weeding and hoeing out young seedlings before the flowers form.

There is, however, a form of biological control that can aid the gardener. Groundsel is susceptible to the fungal rust pathogen (Puccinia lagenophorae). This pathogen arrived in Great Britain from Australia in the early 1960s. Since then, it has become well established and outbreaks on groundsel start to become obvious in mid- to late-summer, especially in warm dry periods.

SCIBlog - 15 August 2022 - image of rust-infected groundsel plant

A fungal pathogen can kill groundsel, a weed that comes through several times a year. Image from Geoff Dixon.

Severe infections weaken, and eventually kill, groundsel plants. Gardeners should take advantage of the infection and remove the diseased weeds before any seeds are produced.

>> How else has climate change changed the way our gardens grow, and what can be done to alleviate its effects? Geoff Dixon investigates.

Professor Geoff Dixon is author of Garden practices and their science, published by Routledge 2019.

Written by Professor Geoff Dixon. You can find more of his work here.

Sustainability & Environment

The wild weather fluctuations wrought by climate change are stressing out our plants. Our resident gardening expert, Professor Geoff Dixon, explains how.

Pests and diseases are familiar causes of plant damage and loss. Less familiar, but becoming more frequent, are stresses resulting from environmental causes.

These are termed abiotic stresses because no living organism is involved. This means there are no visible signs of pests or pathogens. Diagnosis and treatment are, therefore, less straightforward. These causes are a result of interactions between the plant genotype and the prevailing or changing environment.

Damage may only become apparent after harvesting and at the point of consumer use. A typical example of this is internal browning or breakdown of Brussels sprouts. Larger sprouts are more susceptible to stress, with dense leaf packing in the bud, particularly in early and midseason cultivars.

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The internal browning of Brussels sprouts is a consequence of plant stress.

A suggested cause is water condensing within the bud, which restricts calcium transport and leads to marginal leaf necrosis (death). This resembles the exudation, or perspiration, of water from leaf edges when growing plants absorb excessive water, flooding the vascular systems following very heavy rainfall and hot weather.


Moisture damage

Oedema is another moisture-induced disorder. Symptoms include unattractive wart-like swellings coalescing on leaves and stems, particularly on Brussels sprouts, cabbages, and cauliflowers. These may rupture, becoming corky with a yellowish or brownish appearance.

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Moisture-induced damage to cabbage leaves.

These symptoms result from high soil moisture content and high relative humidity associated with hot days and cool nights. Both internal browning and oedema can be minimised by improving soil structure, encouraging rapid drainage by deep cultivation or growing plants on raised beds.

Improving soil structure is becoming an important way to control salt accumulation. Soil structure can be badly damaged by flooding that brings in polluted water. In subsequent vegetable and fruit crops, plant water uptake, nutrient use efficiency, and photosynthesis are all impaired. The effects are seen in poor germination, burnt leaf margin, stunting, and wilting. This damage will be particularly severe with highly organic soils.

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Salt accumulation in onion crops. Improving soil structure is one way of addressing this problem.

Abiotic disorders are becoming more common in commercial crops and this is likely to be reflected in gardens and allotments. That is an effect of climatic change, with generally hotter and wetter conditions interspersed by droughts and freezing events.

As a result, plant growth is erratic and exhibits abiotic disorders. Plant breeders, especially in Asia, are actively seeking genetic solutions that will create crops capable of withstanding erratic environments. In parallel,the agro-chemical industry is producing environmentally sustainable compounds and biostimulants to help combat these problems.

>> How else has climate change changed the way our gardens grow, and what can be done to alleviate its effects? Geoff Dixon explored this issue further.

Professor Geoff Dixon is author of Garden practices and their science, published by Routledge 2019.

Agrifood

What is so special about rainbow chard pigments, and what does this tasty plant have in common with cacti? The SCI Horticulture Group explains all, ahead of their appearance at BBC Gardeners’ World Live in Birmingham from 16-19 June.

The origins of chard

Chard (Beta vulgaris, subspecies vulgaris) is a member of the beetroot family and is grown for its edible leaf blades and leaf stems. Chard, sugar beet, spinach and beetroot have all been domesticated from the same wild ancestor species – sea beet (Beta vulgaris, subspecies maritima). Another food crop from the same botanical family is quinoa.

SCI Blog - 15 June 2022 - image of rainbow chard growing in ground
The term chard comes from the 14th century French word carde, which means artichoke thistle.

Nutritional properties

Chard's leaves are a valuable source of mineral nutrients, with a normal serving of 100g containing: 24% of our daily magnesium needs, 17% of iron, 16% of manganese, and 12% of both potassium and sodium. The same portion can provide 22% of our daily vitamin C needs, 13% of vitamin E, and 100% of our vitamin K.

>> What gives chillis their heat? The SCI Horticulture group has explored the weird and wonderful world of chillis.

The edible petioles (leaf stems) of Swiss chard are typically white, yellow, or red. Lucullus and fordhook giant are cultivars with white petioles. Canary yellow has yellow petioles and red-ribbed forms include ruby chard and rhubarb chard. Rainbow chard is a mix of coloured varieties, often mistaken for a variety unto itself.

The pigments that produce these colours belong to a special group – known as the betalains. These pigments are found only in species of one small section of the plant kingdom called caryophyllales. The pigments in the rest of the plant kingdom have different chemical structures, made up of only carbon, hydrogen and oxygen, whereas the betalain chemical structures also contain nitrogen.

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Rainbow chard contains betalains, as do cacti, pokeweed, and (above) bougainvillea.

The many uses of chard pigments

The colourful pigments in plants not only contribute to the beauty of our gardens – they advertise the presence of flowers to pollinators or fruits to dispersal agents. Others deter herbivores by tasting bitter or act as a sunscreen to protect from strong ultraviolet light.

The vivid pigments found in chard are particularly useful. Betanin is the best-known pigment from this group and gives rise to the striking colour of beetroot. It is used commercially as a natural food dye, can help preserve food, and contains antioxidant properties.

SCI Blog - 15 June 2022 - image of chemical structure of betanin

Betanin, the pigment that makes beetroot (and poop) red.

Some people are unable to metabolise betanin, which gives rise to a phenomenon known as beeturia – where human waste is coloured red by the betanin.

Cooking with chard

When cooking with chard, it can be treated as two separate vegetables – the leafy part and the crunchy petiole. Blitva is a traditional Croatian dish made from the leafy part, often cooked along with potatoes and served with fish.

SCI Blog - 15 June 2022 - image of Blitva

Blitva is made with chard, potato, olive oil, and garlic.

Chard stalks sautéed with lemon and garlic forms another popular side-dish, while lovers of Italian cuisine can turn rainbow chard into a pesto with pine nuts, parmesan and basil.

Find us at BBC Gardeners’ World Live

From 16-19 June, the SCI Horticulture Group will tell the public all about the hidden chemistry behind their favourite fruit and vegetable plants at the National Exhibition Centre in Birmingham for BBC Gardeners’ World Live. If you’re curious to learn all about rainbow chard, chillis, and strawberries, pop by and say hello!.

>> Written by the SCI Horticulture Group and edited by Eoin Redahan. Special thanks to Neal Price from Chillibobs, Martin Peacock of ZimmerPeacock, Hydroveg, and The University of Reading Soft Fruit Technology Group for supporting the work of the SCI Horticulture Committee at BBC Gardeners’ World Live.

>> The SCI Horticulture Group brings together those working on the wonderful world of plants.

Agrifood

Which molecules give strawberries their distinctive smell, how are experts using different types of light to grow them all year round, and just how many of them do we eat? The SCI Horticulture Group told us all about this beloved fruit ahead of their appearance at BBC Gardeners’ World Live in Birmingham from 16-19 June.

Where did strawberries originate?

The woodland strawberry (Fragaria vesca) was first cultivated in the 17th century, but the strawberry you know and love today (Fragaria x ananassa) is actually a hybrid species. It was first bred in Brittany, France, in the 1750s by cross-breeding the North American Fragaria virginiana with the Chilean Fragaria chiloensis.

The strawberry is a member of the rose family, as are many other popular edible fruits such as apples, pears, peaches, and plums. It is the most commonly consumed berry crop worldwide.

SCI Blog - 10 June 2022 - sketch of strawberries and cream on tennis racket
People in the UK consume an average 3kg of strawberries every year. Perhaps a certain sporting event has something to do with it…

How many do we eat?

A staggering 9 million tonnes of strawberries are produced globally each year, and their popularity certainly extends to UK shores, and not just during Wimbledon. In the UK alone, the average per capita consumption of strawberries is about 3kg a year!

Domestic strawberry production provides almost all the required fruit for the UK market from March to November; and in 2020, 123,000 tonnes of strawberries were produced within the UK.

This stands in stark contrast to the 50,000 tonnes produced in 1985, when UK strawberries were only produced during June and July. Researchers are currently trying to extend the UK growing season to all year round.

SCI Blog - 10 June 2022 - sketch of women about to eat strawberry
She certainly likes the smell of strawberries, but what gives them that distinctive aroma?

What about the chemistry of their distinctive smell?

The characteristic strawberry aroma consists of many different volatile organic chemicals – more than 360 have been observed in fresh strawberries. Which molecules are present, and in what concentrations, depends on the particular cultivar and how mature or ripe it is.

The most common kinds of chemical are furanones and esters. Esters (such as methyl butanoate) account for more than one third of the observed molecules and 25–90% of the volatiles from any one cultivar.

These molecules are responsible for the fruity and floral notes of the aroma. The most characteristic furanone that gives rise to the characteristic strawberry odour is DMHF.

SCI Blog - 10 June 2022 - image of strawberries turned into two santas
Pictures like this only increase demand for strawberries out of season.

How to produce strawberries all year...

To optimise strawberry growing conditions, researchers are investigating the influence of temperature, photo-period (response to daily, seasonal, or yearly changes in light and darkness), growth hormones, night-break lighting and CO2 enrichment on flowering and fruiting timing, yield, and quality.

Optimal chilling models are also being developed for both June-bearers and ever-bearers. Critically, a careful and detailed evaluation of the environmental and economic costs of producing winter UK strawberries compared to imports is being undertaken.

Extending the growing season in the UK would have a number of benefits, such as; meeting the increasing demand for out-of-season strawberries while increasing food security, reducing food miles, contributing to public health, providing continued employment, and supporting sustainable farming.

>> Are you a keen gardener? Our resident gardening expert, Geoff Dixon, provides plenty of gardening tips for you on the SCIBlog.

Improving the fruit's nutrient profile

The nutrient content of strawberries is dependent in part on the plant’s growing conditions. The interaction between light intensity and root-zone water deficit stress is being examined to improve berry nutrient content. Researchers are also investigating how to apply this to commercial strawberry production in total environment-controlled agriculture systems.

See how a college in Finland is harnessing LEDs to power a vertical strawberry farm!

LED light colour and strawberry growth

Light emitting diode (LED) lighting increases yields in out-of-season strawberry production. LEDs have a higher energy efficiency than traditional horticultural lighting and come in a range of single colours with varying efficiencies and effects on plant growth.

Red LEDs convert energy into light (and drive photosynthesis) most efficiently, followed by blue, green, and far-red, respectively. However, red light alone is not sufficient for optimum plant growth. Blue light controls flowering, promotes stomatal opening (pores found in various parts of the plant), inhibits stem elongation, and increases secondary metabolites (organic compounds produced by the plant), thereby improving flavour.

Additional green LEDs, which appear white, improve visibility for workers. These lights can also penetrate deeper into the plant canopy, improving photosynthesis. Far-red light produces shade avoidance responses such as canopy expansion and earlier flowering, which can be beneficial for increased light capture and earlier fruiting.

SCI Blog - 10 June 2022 - image of strawberry slice on petri dish>
Confirmed strawberry.

Who is carrying out strawberry research in the UK?

The Soft Fruit Technology Group at the University of Reading is just one of the institutions providing research to support the UK strawberry industry. The main areas of research are plant propagation, crop management, and production systems.

Find us at BBC Gardeners’ World Live

From 16-19 June, the SCI Horticulture Group will tell the public all about the hidden chemistry behind their favourite fruit and vegetable plants at the National Exhibition Centre in Birmingham for BBC Gardeners’ World Live. If you’re curious to learn all about strawberries, chillis, and chard, pop by and say hello!

>> Written by The SCI Horticulture Group. Special thanks to Neal Price from Chillibobs, Martin Peacock of ZimmerPeacock, Hydroveg, and The University of Reading Soft Fruit Technology Group for supporting the work of the SCI Horticulture Committee at BBC Gardeners’ World Live.

Agrifood

How do flowers use fragrance to attract pollinators, and how do pollution and climate change hamper pollination? Professor Geoff Dixon tells us more.

‘Fragrance is the music of flowers’, said Eleanour Sophy Sinclair Rohde, an eminent mid 20th century horticulturist. But they are much more than that. Scents have fundamental biological purposes. Evolution has refined them as means for attracting pollinators and perpetuating the particular plant species emitting these scents.

There are complex biological networks connecting the scent producers and attracted pollinators within the prevailing environment. Plants flowering early in the year are generalist attractors. By late spring and early summer, scents attract more specialist pollinators as shown by studies of alpines growing in the USA Rocky Mountains. This is because there is a bigger diversity of pollinator activity as seasons advance. Scents are mixtures of volatile organic compounds with a prevalence of monoterpenes.

Environmental factors will affect scent emission. Natural drought, for example, changes flower development and reduces the volumes and intensity of scent production. The effectiveness of pollinating insects, such as bees, moths, hoverflies and butterflies is reduced by aerial pollution.

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Pheasant’s eye daffodils (Narcissus recurvus).

Studies showed there were 70% fewer pollinators in fields affected by diesel fumes, resulting in lower seed production. Pollinating insects do not find the flowers because nitrogenous oxides and ozone change the composition of scent molecules.

Extensive studies of changes in flowering dates show that climate change can severely damage scent–pollinator ecologies. Over the past 30 years, blooming of spring flowers has advanced by at least four weeks. Earlier flowering disrupts the evolved natural synchrony between scent emitters and insect activity and their breeding cycles. In turn that breaks the reproductive cycles of early flowering wild herbs, shrubs and trees, eventually leading to their extinction.

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The lilac bush, known for its evocative scent.

Heaven scent

Scents provide powerful mental and physical benefits for humankind. Pleasures are particularly valuable for those with disabilities especially those with impaired vision. Even modest gardens can provide scented pleasures.

Bulbs such as Pheasant’s eye daffodils (Narcissus recurvus) (illustration no 1), which flower in mid to late-spring, and lilacs (illustration no 2) are very rewarding scent sources.

Sweetly perfumed annuals such as mignonette, night-scented stocks, candytuft and sweet peas (illustration no 3) are easily grown from garden centre modules, providing pleasures until the first frosts.

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Sweet peas are easily grown from garden centre modules.

Roses are, of course, the doyenne of garden scents. Currently, Harlow Carr’s scented garden, near Harrogate, highlights the cultivars Gertrude Jekyll, Lady Emma Hamilton and Saint Cecilia as particularly effective sources of perfume. For larger gardens, lime or linden trees (Tilia spp) form profuse greenish-white blossoms in mid-season, laden with scents that bees adore.

Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.

Agrifood

How much soil cultivation do you need for your vegetables? Professor Geoff Dixon explains all.

Cultivating soil is as old as horticulture itself. Basically, three processes have evolved over time. Primary cultivation involves inversion which buries weeds, adds organic matter and breaks up the soil profile, encouraging aeration and avoiding waterlogging.

Secondary cultivation prepares a fine tilth as a bed for sowing small seeded crops such as carrots or beetroot. In the growing season, tertiary cultivation maintains weed control, preventing competition for resources (illustration no. 1) such as light, nutrients and water while discouraging pest and disease damage.

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Lettuce and seed competition

The onset of rapid climate change encouraged by industrialisation has focused attention on preventing the release of carbon dioxide into the atmosphere. Ploughing disturbs the soil profile and accelerates the loss of carbon dioxide from soil.

It is also an energy intensive process. Consequently, many broad acre agricultural crops such as cereals, oilseed rape and sugar beet are now drilled directly without previous primary cultivation. An added advantage is that stubble from previous crops remains in situ over winter, offering food sources for birds. The disadvantages of direct drilling are: increased likelihood of soil waterlogging and reduced opportunities for building organic fertility by adding farmyard manure or well-made composts.

Overall, primary and secondary cultivation benefit vegetable growing. The areas of land involved are far smaller and the crops are grown very intensively. Vegetables require high fertility, weed-free soil, good drainage and minimal accumulation of soil-borne pests and diseases.

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Frost action breaking down soil clods

Digging increases each of these benefits and provides healthy physical exercise and mental stimulation. Frost action on well-dug soil breaks down the clods (illustration no. 2). Ultimately, fine seed beds are produced by secondary cultivation (illustration no. 3), which encourage rapid germination and even growth of root and salad crops.

Tertiary cultivation to prevent weed competition is also of paramount importance for vegetable crops. Competition in their early growth stages weakens the quality of root and leafy vegetables, destroying much of their dietary value. Regular hoeing and hand removal of weeds are necessities in the vegetable garden.

SCIblog - Professor Geoff Dixon - Soil Cultivation - image of Raking down soil producing a fine tilth

Raking down soil producing a fine tilth

Ornamental and fruit gardens similarly benefit from tertiary cultivation. Weeds not only provide competition but are also unsightly, destroying the visual image and psychological satisfaction of these areas.

Lightly forking over these areas in spring and autumn encourages water percolation and root aeration. Once established, ornamental herbaceous perennials and soft and top fruit areas benefit greatly from the addition of organic top dressings. Over several seasons these will augment fertility and nutrient availability.

Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.

Agrifood

Gardens in December should, provided the weather allows, be hives of activity and interest. Many trees and shrubs, especially Roseaceous types, offer food supplies especially for migrating birds.

Cotoneaster (see image below) provides copious fruit for migrating redwings and waxwings as well as resident blackbirds. This is a widely spread genus, coming from Asia, Europe and northern Africa.

Cultivated as a hedge, it forms thick, dense, semi-evergreen growth that soaks up air pollution. In late spring, its white flowers are nectar plants for brimstone and red admiral butterflies and larval food for moths. Children and pets, however, should be guided away from the attractive red berries.

SCIblog - 7 December 2021 - The December Garden by Prof Geoff Dixon - Caption 1 image of Cotonester franchetti fruit

Cotonester franchetti | Image credit: Professor Geoff Dixon.

Medlars (Mespilus germanica) offer the last fruit harvest of the season (see image below). These small trees produce hard, round, brownish fruit that require frosting to encourage softening (bletting).

Its soft fruit can be scooped out and eaten raw and the taste is not dissimilar to dates. Alternatively, medlar fruit can be baked or roasted and, when turned into jams and jellies, they are delicious, especially spread on warm scones.

Like most rosaceous fruit, medlars are nutritionally very rich in amino acids, tannins, carotene, vitamins C and B and several beneficial minerals. As rich sources of antioxidants medlars also help reduce the risks of atherosclerosis and diabetes.

SCIblog - 7 December 2021 - The December Garden by Prof Geoff Dixon - Caption 2 image of Medlar fruit (Mespilus germanica)

Medlar fruit (Mespilus germanica) can be turned into jams and jellies | Image credit: Professor Geoff Dixon.

Garden work continues through December. It is a time for removing dead leaves and stems from herbaceous perennials, lightly forking through the top soil and adding granular fertilisers with high potassium and phosphate content.

Top fruit trees gain from winter pruning, which opens out their structure, allowing air circulation when fully laden with leaves, flowers and fruit. Fertiliser will feed and encourage fresh root formation as spring progresses.

The vegetable garden is best served by digging and incorporating farm yard manure or well-rotted compost, which adds fertility and encourages worm populations. The process of digging is also a highly beneficial exercise for the gardener (see illustration no 3).

SCIblog - 7 December 2021 - The December Garden by Prof Geoff Dixon - Caption 3 image of turning the soil

Turning the soil isn’t only good for your garden - it boosts your wellbeing | Image credit: Professor Geoff Dixon.

Developing a rhythm with this task supports healthy blood circulation and, psychologically, provides huge mental satisfaction in seeing a weedy plot transformed into rows of well-turned bare earth.

When the weather turns wet, windy and wintery it provides opportunities for cleaning, oiling and sharpening tools, inspecting stored fruit and the roots of dahlias kept in frost-proof conditions.

Finally, there is always the very relaxing and pleasant task of reading through seed and plant catalogues and planning what may be grown in the coming seasons.

Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.

Agrifood

How has climate change changed the way our gardens grow and what can be done to alleviate its effects? Professor Geoff Dixon tells us more.

Climate has changed on Earth ever since it solidified and organic life first emerged. Indeed, the first photosynthesising microbes changed the atmosphere from carbon dioxide rich to oxygen rich over millions of years. What we now face is very rapid changes brought about by a single organism, mankind, through industrialisation.

The effects of change are very evident in gardens. Over a generation, leaf bud breaking and flowering by early spring bulbs, herbaceous plants, shrubs and trees has advanced by at least four weeks (see main image of Cyclamen hederifolium).

Latter spring displays have advanced by at least two weeks. This is caused by milder, wetter winter weather, encouraging growth. The danger lies in the increasing frequency of short sharp spells of severe frost and snow. These kill off precocious flowers and leaves which trees especially cannot replace.

desiccated cracked soil

Desiccated, cracked soil.

Increasingly, the summer climate is becoming hotter and drier. Since the Millennium there has been a succession of hot droughts. These seriously limit scope for growing vegetables, fruit and ornamentals unless irrigation is regularly available. Drought also damages soil structure especially where there is a high clay content by causing cracking and the loss of plant cover (see image of desiccated, cracked soil above).

Cracking disrupts and destroys the root systems of trees and shrubs in particular. The effects of root damage may not become evident until these plants die in the following years. 

Climate change is apparently advantageous for microbes. Detailed surveys show that fungal life cycles are speeding up, increasing the opportunities for diseases to cause damage. Even normally quite resilient crops such as quince are being invaded during milder, damper autumns (See image of brown rot on quince fruit below). Throughout gardens, the range and aggressiveness of pests and disease is increasing.

Brown rot on quince fruit

Brown rot (Monilia laxa) on quince fruit.

However, each individual garden or allotment, no matter its size, can contribute to reducing the rate of climate change. Simple actions include the removal of hard landscaping, and planting trees and shrubs reduces carbon emissions.

Using electric-powered tools and machinery in place of petrol or diesel has similar advantages. Tumbling down parts of a garden into native flora, and perhaps encouraging rarer plants such as wild orchids or fritillarias, mitigates climate change. Such areas may also form habitats for hedgehogs or slow worms, increase populations of bees, butterflies and moths and encourage bird life. 

Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.

All images from Professor Geoff Dixon.

Agrifood

Lilies provide gloriously beautiful and well scented flowering border plants. Choose flowering size bulbs in the garden centre or from a catalogue. Grow these through the winter potted in a general garden compost placed in an unheated greenhouse or cold frame. By March or early-April, substantial green shoots will have formed from the bulbs and they can be transplanted into the garden.

Lilies need a sunny border and very fertile soil to encourage vigorous root growth capable of supporting the flowering spike and ancillary bulbs as they are initiated. This produces magnificent flowers and an increasing colony of bulbs that will spread and become established over future seasons.

SCIblog - 21 September 2021 - Looking after your lilies - image of Lilium longiflorum / Easter Lily

Lilium longiflorum, often called the Easter lily | Image credit: Professor Geoff Dixon.

Regular watering and feeding with nutrients are needed, especially potassium, which encourages root and shoot growth. Stake the flower spike as it grows, giving support for the flowers because they are heavy when fully open and easily damaged by winds.

Rewards come in mid-summer with magnificent colourful flowers and wonderful perfumes on warm evenings. Apart from severe winters, lilies are hardy garden plants unless they are from groups specified as tender and requiring protection. In the autumn, simply cut down the flowering spike and remove any fallen foliage.

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Buds developed on lily scales after culturing | Image credit: Professor Geoff Dixon.

The Lilium genus has about 100 species originating worldwide mainly from north temperate areas of Europe, Asia and America. The colour range includes white, yellow, orange, pink, red and purple. Plant breeders in The Netherlands, Japan and North America have produced a huge range of multi-coloured hybrids.

Taxonomically, Lilium is divided into divisions, of which the Turk’s Caps, Martagons and American hybrids are popular. The most destructive pest is the scarlet lily beetle (Lilioceris lilii) which devours foliage, flowers and bulbs. The first signs of trouble are shot holes in the foliage. Picking off beetles and larvae is an effective means of dealing with low-level infestations.

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Comparison of lily bulbils growing from scale leaves, immature bulb and flowering size bulb | Image credit: Professor Geoff Dixon.

Asexual propagation is a simple and enjoyable occupation. Divide a good-sized bulb into its scales. Choose healthy scales from the outer rings and place these in a plastic box containing damp kitchen paper and place in an airing cupboard. After about 10-12 weeks, small bulbils will have formed on each scale.

Select the boldest mother scales and bulbils and plant in a tray of seedling compost and grow in the greenhouse. After two or three months the most vigorous young plants can be potted individually. Eventually these are planted in the garden and will develop into flowering size bulbs after two or three years.

Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.

Agrifood

Main image: Pea crop | Image credit: Geoff Dixon

Peas are a very rewarding garden crop. Husbandry is very straightforward, producing nutritious yields and encouraging soil health by building nitrogen reserves for future crops.

Rotations usually sequence cabbages and other nitrogen-demanding crops after peas. This is a sustainable way to use the organic nitrogen reserves left by pea roots resulting from their mutually beneficial association with benign bacteria. These microbes capture atmospheric nitrogen, producing ammonia, nitrites and nitrates in a sequence of natural steps.

Peas originated in the Mediterranean. They were cultivated continuously by ancient civilisations and through medieval times, and are now the seventh most popular vegetable.

SCIblog - 26 July 2021 - Peas please - image of pea seeds - photo by Geoff Dixon

Illustration 1: Pea seeds | Image credit: Geoff Dixon

In bygone centuries, peas provided a protein source for the general population as cooked meals of pea soup and pease pudding helped keep famine at bay before the introduction of potatoes. In the 18th century, French gardeners working for the aristocracy produced fresh peas using raised and protected beds of fermenting animal manure. The composting processes produced heat and released carbon dioxide, stimulating rapid growth.

Generally, however, eating fresh peas only gained popularity in the 20th century as canned and then quick-frozen foods were invented, and large-scale technological development enabled mechanised and automated commercial precision cropping. In recent times, retail market demand has returned for unshelled podded peas – a manually picked crop known colloquially as ‘pulling peas’.


How to grow peas

Seeds can be sown directly (illustration 1) or transplants (illustration 2) can be raised under protection, giving an early boost for growth and maturity. Peas are cool season crops. They grow best at 13-18°C and mature about 60 days after sowing.

SCIblog - 26 July 2021 - Peas please - image of pea seedlings - photo by Geoff Dixon

Illustration 2: Pea seedlings | Image credit: Geoff Dixon

Some cultivars such as Meteor can be grown over winter, preferably protected with cloches for very early cropping. The spring sown The Sutton cultivar group (CV) gives rapid but modest returns, and main crop CVs, such as Hurst Green Shaft, deliver the heaviest returns (illustration 2). This cultivar forms several long, well-filled pods at the fruiting nodes.

Sugar peas or mange tout – where the entire immature pod is eaten – is a popular fresh crop, while quick-growing pea shoots that mature in 20 days from sowing are excellent additions for salads or as garnishes for warm cuisine.

Human health benefits significantly by including peas in the diet. As well as being an excellent protein source, they produce a range of vitamins and nutrient elements. Their coumestrol content aids the control of blood sugar levels, helping combat diabetes, heart diseases and arthritis.

So, it’s certainly worth finding a spot for this versatile vegetable in your garden.

Written by Professor Geoff Dixon, author of Garden practices and their science.