Growing Together
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Few things give as much pleasure as raising plants from seed. It can be substantially less expensive than buying plants and there is a huge choice of varieties. Some are less easy to raise than others but we hope that, with the help of this guide, we can give you the best chance of success. We believe that anyone can do it and that there are no such things as green fingers – or the lack of them!
A seed is an incredible feat of packaging. It is a small plant in embryo form, complete with a food store and all protected by a
tough outer skin. When a seed is exposed to a favourable combination of moisture and warmth, it should start to take up water. This will cause it to swell and then the skin will burst allowing the embryo plant to start growing. This is known as germination.
While we have found that a few seeds require special conditions to germinate, the basic requirements for success are; correct watering,
correct temperature, suitable compost/soil, correct sowing depth and, in some cases, light.
In our experience, one of the main causes for seeds not germinating is either over or under watering. You should never allow seed to dry out before watering, nor should you waterlog the soil or compost. You should, however, always keep the seed moist.
The range of temperatures that seeds prefer for germination varies considerably but if it is too cold they may rot and if it is too hot they may remain dormant. All our seed packets clearly show the recommended time of year to sow and whether they need to be sown indoors/under glass or can be sown outside.
For seeds sown in pots or trays, garden soil should never be used as it may contain weed seeds and other unwanted pests. Rather than garden soil, use a good quality seed or general purpose compost recommended for seed sowing. When planting outside, the soil needs to be broken up to a fine consistency (known as tilth) and be moist but not too wet.
The depth at which seeds should be sown varies with smaller varieties needing to be at or very near the surface. For the correct depth, always consult the packet.
Although most seeds do not require light to germinate, some varieties do need to be sown on or near the surface.
The first thing that we would say is – don’t be in too much of a rush to sow your seeds. Sowing too early or too late can result in the seeds not germinating. Always use the stated periods as a guide only as they are based upon the UK average and therefore it is best to wait until your soil is beginning to warm up.
Plants that are not frost hardy need a longer growing season than our climate naturally provides. Because of this, you will often need to sow these seeds indoors in a greenhouse, in a conservatory, on a windowsill or possibly in a
cold frame. Use clean pots, trays, propagators, labels or other growing equipment. This will reduce the possibility of disease affecting the fragile young
seedlings.
When sowing seeds inside or in a greenhouse it is best to use a good seed sowing compost. As a tip, bring compost in from the outside on a cold day, to let it warm up before use. When sowing, you can use any container as long as it is clean and has drainage holes. However, small plastic pots or seed trays are most commonly used. There is no benefit to using larger pots than necessary as the seedlings will not be in them for very long. For larger seeds that develop deep root systems
such as sweet peas and runner beans, you can use extra deep ‘rootrainers’. These will allow transplantation with minimal root disturbance. Fill the tray or pot to the rim with compost. Tap the container sharply on the bench or table to settle the compost then gently firm it down with the base of a similar size pot or tray. Do not overfirm the compost as this will restrict drainage and root penetration. There should now be enough gap to the top of the tray or pot to cover the seeds with further compost, if necessary.
One of the most common mistakes made during sowing is to water directly onto the top of the compost. This will compact the surface and undo all the careful work you have done so far. The best way to water is from the bottom – stand the trays or pots in about 2cm of water and leave them until the surface becomes wet. Then remove them and allow to drain for at least 30 minutes.
Always sow thinly. Sowing seeds too thickly will result in poor growth due to overcrowding and the seedlings competing with each other. Seedlings may become more prone to disease and be more difficult to transplant.
Larger seeds are easy to position with your fingers, it is easier to sow very small seeds if you first mix them with fine dry sand.
Very fine seeds should be pressed gently into the surface but left exposed. Seeds which require light should be treated similarly. For all other seeds follow the instructions on the seed packet but a good rule of thumb is to cover to a depth of about three times their diameter. To cover small to medium seeds with a thin layer of compost, why not try using a fine flour sieve? Alternatively, we recommend using fine vermiculite as it holds more moisture than compost but remains well aerated. It is also sterile and won’t form a cap, a hard layer that could create a barrier to germinating seedlings.
Only very large seeds such as beans, marrows and nasturtiums require a different approach and we have found that they are best inserted into small holes of the appropriate depth.
Once sown, your seeds should be examined at least once a day. Further watering should not be required before germination unless the surface of the compost shows any sign of drying out. At the first signs of germination, remove any paper cover and, if the tray or pot is in a dark place, transfer it to a location where it is in full light, still equally warm but not in direct sun. When germination is well under way, remove the glass or plastic cover so that air can circulate around the seedlings. You should remember that when several different varieties are sown in the same container, not all of the seedlings will start to appear at the same time.
When most of your seeds have germinated, move the trays or pots to a slightly cooler location. Those on a windowsill should be turned daily due to the seedlings’ tendency to grow towards the light. You must ensure the seedlings are kept moist at all times but, to avoid over-watering, always wait until the compost surface starts to dry before carefully watering again.
As seedlings which are not already in cells or plug trays become large enough to handle, they should be transplanted to other containers to give them more space to grow. This is known as ‘pricking out’. The right time for pricking out is usually when seedlings have developed their first set of true leaves but some plants, such as petunias, which have very small seedlings may need to develop more than one set before they are ready. Seedlings should not be left too long as their rapidly growing roots quickly become difficult to untangle and relocate without causing damage.
Seedlings should always be lifted carefully using an implement such as a pencil or an old fork from the kitchen. If they are too crowded to lift singly, lift them in clumps and then, gently, tease them apart causing as little damage to the roots as possible. Some, such as lobelia, can be left in small clumps. Seedlings should always be held by their leaves, never by their stems as, if the stems get crushed, the plants will die.
Place the roots of each seedling into a hole in the fresh compost, firming it in gently afterwards. In trays, the holes should be about 3cm apart. We suggest planting the seedling slightly deeper than it was before to ensure that it is well supported and won’t fall over. This is particularly important for seedlings such as tomatoes, which tend to have a long stem below the first leaves (the seed leaves or ‘cotyledons’) but the lowest leaves should always be above the compost surface. When pricking out is complete, pots or trays should be watered from below or gently from above with a fine rose. You must never use very cold water on seedlings at any time.
If you are growing a mixed variety, don’t just prick out the largest seedlings and discard the rest as it is common that not all of the colours germinate at the same time or rate. Unless all the seedlings are given an equal chance, it is possible to end up with only one or two of the colours.
For growing on, the pricked out seedlings need to be returned to a position where the temperature and light are similar to their previous location. They should then be kept moist but no feeding should be necessary until they are well established. If they become overly large or crowded before they can be planted out, don’t be afraid to ‘pot them on’ again into larger cells or pots.
Before they can be planted outside your seedlings will need to get used to the conditions in your garden. To acclimatise them to life in the open air, you should put them outside in a warm and sheltered spot during the day and bring them in again at night for a period of about two weeks. This process is referred to as ‘hardening
off’. An alternative to moving seedlings in and out is to transfer them to a cold frame where they can be covered over at night.
When all danger of frost has passed, typically around the end of May or first week of June, planting out can begin. Ideally you will have dug the soil over and enriched it with compost or other well-rotted organic matter beforehand.
Water your plants well before you gently remove them from their trays or pots and plant them carefully, spacing them according to the directions on the seed packets. Finally firm them in well and water again thoroughly.
You will find that many vegetables, herbs and flowers can be sown directly in the garden. Some root crops and annual flowers only do well if sown directly in their final positions. Others are best sown in a seedbed and transplanted to their permanent positions when large enough. As a general rule of thumb, don’t start sowing
directly outdoors until you see annual weeds such as nettles are growing vigorously and the soil has dried sufficiently so as not to stick to your boots.
A seedbed is a small area of your garden specifically set aside for the raising of your seedlings. In a sheltered, but not shaded spot. In such beds it is much easier for you to give slower growing and more delicate plants the extra attention they need. Raising seedlings in seedbeds is particularly valuable for plants such as wallflowers and vegetables such as brassicas (cabbages, cauliflowers etc.), particularly those with expensive seeds.
Construction of a seedbed is essentially the same as the preparation of any other area for seed sowing. On poorly drained soils, a raised seed bed can be made within an edging oftimber. If your soil is not good for seed raising, your bed can be made of imported topsoil. As your seedlings aren’t going to grow to full size there, the rows in a seedbed can be quite close together - about 15cm apart will be fine.
