How to Grow Plants from Seed

Raising Plants from Seed

The technique of raising plants from seed rather than buying ready-grown subjects is particularly important to organic gardeners because the plants will be organic right from the outset. Growing from seed is also important because it gives much more choice in what you can cultivate: you can pick types and varieties that are well suited to a particular soil or situation, along with those that are resistant to disease. Unlike plants, seeds rarely carry diseases, so there is much less risk of introducing problems into the garden. However, germinating seeds and young seedlings are very vulnerable to pests and diseases as they do not have the resources to recover from an attack. The faster and stronger they grow, the more likely they are to survive and be healthy.


Sources of seed

How to Grow Plants from Seed Unfortunately, there is little organically grown seed available. You can save the seed of some crops and flowers from your own garden if you have time and space.

As the best alternative, use conventionally grown seeds that have not been chemically dressed with fungicide between the time they were harvested and when they were packeted. However, only certain seeds are fungicide dressed before sale and this is declared on the packet. Also, it should say in the catalogues of some firms whether or not their seed has been treated in this way.


Getting a good start

If seeds are to germinate quickly and seedlings grow vigorously they must be grown in the correct way and have the right conditions.


Good seed

Make sure you get good-quality seed. Seed deteriorates in storage, not only affecting the percentage of seed which germinates but also the germination time and the vigour of the resultant seedlings. Always store seed in a sealed packet in a cool dry place.

The lifetime of different seeds varies, but many will still germinate after three or four years if stored well. If you are doubtful about any of your seed stocks, put a few on moist kitchen towel in a warm place so that you can see how many germinate.


Correct temperature

In general, plants that need a warm climate in which to grow need higher temperatures to germinate. Consequently, broad beans, which are cool season crops, will germinate at a temperature of about 5°C (41°F), whereas courgettes need a minimum temperature of 12 or 13°C (54 or 56°F), and lobelia needs at least 15°C (59°F). It is best to aim for temperatures a few degrees above these minimum figures.

Up to a point, the higher the temperature the quicker the seeds will germinate and the more rapidly the seedlings will grow. However, too high a temperature can be detrimental, and for some seeds this threshold is easily reached. Butterhead lettuce, for example, does not germinate well above about 25°C (77°F) — a temperature often exceeded on a hot summer’s day.

It is easier to reach higher temperatures in spring if seeds are sown in pots and trays placed in a greenhouse and transplanted later. In summer, seeds that are temperature-sensitive can be sown in containers and put in a cool place until they germinate. However, there are also ways of raising or lowering the temperature of seedbeds outside to accommodate different needs (see below).


Moisture and air

Seeds need moisture and air to germinate, but too much moisture will lower the temperature, drive out air and encourage fungal diseases. Emerging seedlings need to be moist but not waterlogged. Getting the right balance is easier if you start your plants off in a greenhouse.

Seeds with hard coats can take a long time to germinate because moisture cannot easily enter the seed, and sometimes you can speed up the process by scarifying them. To do this, rub hard-coated seed gently between two sheets of sandpaper. Once the seed coat has been weakened moisture can penetrate easily and hence speed up the germination process. Examples of commonly grown seeds which need this treatment include cranesbills (Geranium spp.), rock roses (Cistus spp.) and vetches (Vicia spp.)

Alternatively, some hard-coated seeds can be softened in water first prior to sowing. To do this, soak them in warm water for several hours; if you put them in a thermos then this will keep the water warm. Examples of seeds which benefit from being soaked like this include morning glory (Ipomoea) and New Zealand spinach (Tetragonia expansa).

For large, hard seeds like sweet pea seeds, it is possible to nick them carefully with a knife.


Light

Most seeds germinate well in both light and dark. However, some germinate much better if they are exposed to the light — a number of wild flowers, herbs and half-hardy annuals, for example. Look for instructions on seed packets for this information.

The seeds must be sown on the surface of the soil or compost and kept moist by a covering of clear polythene or glass if necessary. There are only a few common seeds which do better in the dark: pansies (Viola) and nemesias (Nemesia) are two examples.

However, all seedlings need good all-round light otherwise they will become weak, spindly and generally sickly-looking.


Pre-chilling

Some seeds, particularly those of wild flowers, require a period of cold before they will germinate. Seeds which are likely to need this treatment include angelica (Angelica archangelica), sweet cicely (Myrrhis odorata), bluebell (Endymion non-scriptus), ramsons (Allium ursinum), some types of poppy (Papaver), cowslip (Primula veris) and primrose (Primula vulgaris). The seed should be put in the fridge for six or eight weeks, after which they should be sown.


Sowing outdoors

There is much you can do to aid germination outdoors, despite the weather.

Do not sow seed until the soil has warmed up in spring. To speed up the process, cover the seedbed with clear polythene or cloches for a week or two before sowing. A well-drained soil warms up more quickly. On heavy soils, raised beds (see Bed System for Growing Vegetables) can help to improve drainage. To cool down the soil for summer sowings of temperature-sensitive seeds, water it well and cover with newspaper, white plastic or other reflective material.

If necessary, water the seedbed the day before sowing — the soil should be just moist. The seeds must make good contact with the soil particles, so rake the bed to give a good tilth: the smaller the seed the finer the tilth should be. There will be adequate supplies of air if the seedbed is well drained. Soils that have previously been mulched with organic matter have a good crumbly surface structure and stay moist without becoming waterlogged.

To sow, draw the end of a trowel blade or the corner of a hoe along a line to make a shallow drill. Small seeds run out of resources if they do not reach the light quickly, so sow them nearer the surface than large seeds. Sow the seeds thinly: space small seeds about 2.5cm (1 in) apart and large seeds, such as peas or beans, at the recommended spacing. Overcrowded seedlings become weak and spindly as they compete for moisture, air and light, and are more at risk from fungal diseases.

Cover the drill with soil or, if the soil is cloddy, use seed compost, leafmould or old potting compost. If the seeds are in danger of drying out, cover the seedbed with plastic film, newspaper or a piece of old carpet to keep moisture in. This is preferable to watering after sowing, which can cause a hard crust or “cap” to form, so hindering the emergence of seedlings. Remove the covering as soon as there are signs of growth.


Sowing inside

You can sow seeds into a single pot or tray and prick out individual seedlings later or sow directly into modules (multi-celled or divided trays). Either way, it is important to use clean containers and a good mixture for sowing into (see Growing Media for Garden Plants).


Using pots and trays

Fill a shallow pot or small tray with moist seed mixture and sow the seeds thinly on the surface. Cover them with a thin layer of seed mixture, except for very fine seeds, which should be left on the surface. Put a piece of glass or clingfilm or a clear plastic bag over the pot to retain moisture and keep it out of direct sunlight. Prick out the seedlings into trays as soon as they are large enough.

The advantage of this method is that the pot takes up little room in a heated propagator where space may be limited. The disadvantages are that this is a time-consuming process and that the growth of seedlings can be upset by pricking out.


Using modules

The advantages of modules is that there is no pricking out and no root disturbance when transplanting. It also allows plants that would normally be sown directly in situ to be started off inside. However, modules do take up a lot of space in a propagator or greenhouse.

Use a sowing mixture which will sustain the growth of the seedlings. Sow seeds as above but directly into the modules, two or three per cell, and take out the extra seedlings as soon as it is practical, leaving one strong seedling to grow on. When the roots fill the module, take out the young plants by pushing them from below and transplant them.

Some vegetable crops can be “multi-sown”. Sow several seeds in each cell and leave them to grow on. Plant each group out as one plant, but spaced wider than normal. This works well for onions and leeks (use six seeds) and beetroot (use two or three), for example. It saves space and time spent on planting out.


Hardening off

Plants sown inside must be acclimatized to the harsher garden conditions. For about a week before planting, stand the trays or modules outside during the day; bring them inside at night or in bad weather until they have hardened off enough to stay outside.


03. February 2011 by Dave Pinkney
Categories: Organic Gardening, Propagating | Tags: , , , | Comments Off on How to Grow Plants from Seed

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