Some plants such as lettuce require cool conditions for germination (<10 oC), a condition known as thermo-dormancy. This reflects the evolution of the wild parent species in cooler environments and growth cycles limited by higher summer temperatures. Transforming live but dormant seed into new healthy self-sufficient plants requires care and planning. The conditions in which seed is stored before use greatly affect the vigour and quality of plants post-germination. Seed which is stored too long or in unsuitable environments deteriorates resulting in unthrifty seedlings.
Seed is either sown directly into soil or into compost designed especially as an aid for germination. These composts contain carefully balanced nutrient formulae which provide larger proportions of potassium and phosphorus compounds which promote rooting and shoot growth. The amounts of nitrogen needed at and immediately post-germination are limited. Excess nitrogen immediately post-germination will cause over-rapid growth which is susceptible to pest and pathogen damage.
Minor nutrients will also be included in composts which ensures the establishment of efficient metabolic activities free from deficiency disorders. Composts require pH values at ~ 7.0 for the majority of seedlings unless they are of calicifuge (unsuited for calcareous soils) species where lime requirement is limited and the compost pH will be formulated at 6.0. Additionally, the pC will be carefully tuned ensuring correctly balanced ionic content avoiding root burning disorders. Finally, the compost should be water retentive but offering a rooting environment with at least 50 percent of the pore spaces filled with air. Active root respiration is essential while at the same time water is needed as the carrier for nutrient ions.
Seedlings encountering beneficial environments delivering suitable temperatures will germinate into healthy and productive plants.
Some plants such as lettuce require cool conditions for germination (<10 oC), a condition known as thermo-dormancy. This reflects the evolution of the wild parent species in cooler environments and growth cycles limited by higher summer temperatures.
Careful husbandry under protection such as in greenhouses provides plants which can be successfully transplanted into the garden. The soil receiving these should be carefully cultivated, providing an open crumb structure which permits swift and easy rooting into the new environment. It is essential that in the establishment phase plants are free from water stress. Measures which avoid predation from birds such as pigeons may also be required.
Netting or the placing of cotton threads above plants helps as a protection measure. Weeds must be removed otherwise competition will reduce crop growth and encourage pests and diseases, particularly slug browsing. Finally, the gardener will be rewarded for his/her work with a fruitful and enjoyable crop!
Seed is one of Nature’s tiny miracles upon which the human race relies for its food and pleasure.
Each grain contains the genetic information for growth, development, flowering and fruiting for the preponderant plant life living on this planet. And when provided with adequate oxygen, moisture, warmth, light, physical support and nutrients germination will result in a new generation of a species. These vary from tiny short-lived alpines to the monumental redwood trees growing for centuries on the Pacific west coast of America.
Humankind has tamed and selected a few plant species for food and decorative purposes.
Seed head of beetroot, the seeds are in clusters.
Seed of these, especially food plants, is an internationally traded commodity. Strict criteria governed by legal treaties apply for the quality and health of agricultural and many horticultural seeds. This ensures that resultant crops are true to type and capable of producing high grade products as claimed by the companies who sell the seed.
Companies involved in the seed industry place considerable emphasis on ensuring that their products are capable of growing into profitable crops for farmers and growers. Parental seed crops are grown in isolation from farm crops thereby avoiding the potential for genetic cross-contamination. With some very high value seed the parent plants may be grown under protection and pollinated by hand.
Samples of seed are tested under laboratory conditions by qualified seed analysts. Quality tests identify levels of physical contamination, damage which may have resulted in harvesting and cleaning the seed and the proportion of capable of satisfactory germination. There may also be molecular tests which can identify trueness to type. Identifying the healthiness of seed is especially important. The seed coat can carry fungal and bacterial spores which could result in diseased crops. Similarly, some pathogens, including viruses, may be carried internally within seed.
Septoria apicola – seed borne pathogen causing late blight of celery
Pests, especially insects, find seed attractive food sources and may be carried with it. Careful analytical testing will identify the presence of these problems in batches of seed.
The capabilities of seed for producing vigorous plants is particularly important with very high value vegetable and salad crops. Vigour testing is a refined analytical process which tracks the uniformity and speed of germination supplemented with chemical tests determining the robustness of plant cells. Producers rely on the quality, uniformity and maturity rates of crops such as lettuce, green broccoli or cauliflower so they meet the strict delivery schedules set by supermarkets. Financial penalties are imposed for failures in the supply chain.
Biology’s seemingly inert tiny seed grains are essential ingredients of humankind’s existence!