Blog search results for Tag: Horticulture

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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.

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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.

SCIblog - 21 September 2021 - Looking after your lilies - image of lily buds

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.

SCIblog - 21 September 2021 - Looking after your lilies - image of lily bulbil comparison

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.

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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.