Growing Plants From Seed

The early stages of a plant's life are its most important. If seedlings are week and spindly, through lack of light or poor growing conditions, it can produce weak and drawn out plants, which are of little use in the garden. So it is important to get this stage right and encourage strong healthy growth from the start. Seeds can either be purchased from a commercial seed grower or you can collect your own, either way, the method of sowing them is the same.

There are basically two methods of sowing seeds; sowing under cover and direct sowing outside. The method you use will depend on the plant variety, time of year and weather conditions. The best advice is to always follow the directions provided on the seed packet. However, if you have purchased seeds from abroad then you may need to confirm the correct sowing conditions for that variety in the UK. Seeds sown too early can suffer from lack of light and space and seeds sown too late may not flower in time before the season ends.

Some seeds require light to germinate, such as the fine seeds of lobelia, and other seeds require total darkness, such as orchids, it all depends on the variety. All seeds need moisture and the correct level of heat to germinate, however, certain seeds, such as alpines, will germinate better if they have had a cold spell before sowing. This is known as cold stratification, which is required to simulate winter conditions, and can be achieved by storing the seeds in a refrigerator for a period of time.

Storing Seeds

Most seeds have an optimum shelf life, which is usually printed on the packet.

The main problem with packet seeds is that you often get far too many in the packet for your immediate needs. However, opened packets can still be stored if you treat them carefully, so they can still be germinated again next season, although results will often not be as a good.

Open seed packets should be kept dry and stored in an airtight container, such as a clean jar, tin or plastic sandwich box that has a tight fitting lid. To ensure they remain dry you can place a sachet of silica gel in with them to absorb any moisture. Keep the storage container in a cool dry place such as a garage, out-house, cellar or the lowest drawer in your refrigerator. Don't store them in a centrally heated room, greenhouse or shed where the temperature can fluctuate.

You can always exchange left-over seeds with a friend or neighbour.

Several internet sites enable users to post details of their spare seeds online. All you usually need to do is join the forum and post the details of your seeds or if you see some seeds you like, you can often simply reply to the posting with an SAE (Stamped Addressed Envelope). The following UK sites offer free seed and plant swaps:

Sowing Seeds Indoors or Under Glass

An average temperature of around 15°C (59°F) is required for good germination for most general plant varieties. If it is not possible to maintain the required temperature artificially, sowing should be delayed until the weather is warmer.

Seeds need both warmth and moisture to germinate and grow. The best results can be achieved by the use of under-soil heat, such as a heated propagator or soil warming cable. If you don't have a heated propagator, and you are starting your seeds off early in the season, you can put them in an airing cupboard or near a radiator until they germinate. Although a warm windowsill should prove adequate for most seedlings.

The most problematic period in a seedling's life cycle is during its transplantation from a seed tray into larger a pot or container. Damage to the roots and leaves can occur if the seedling is not handled correctly. Also the root disturbance can set back the growth of the plant. Seedlings should be gently eased out of the soil using a widger or small dibber under the roots, and lifted gently by their seed leaves. A suitable hole should be made in the potting compost and the roots lowered in, then the soil should be pricked all around it with a dibber to firm it in.

Disturbance can be minimised by sowing seeds directly into multi-cell trays. Sow one or more seeds in each cell, or several in the case of smaller seeds. Once they germinate the weaker seedlings can be thinned out, leaving the strongest to grow-on undisturbed. Once the plants grow to fill the cell, the individual plantlets can be pushed out and potted on or planted direct into their final flowering positions with little disturbance to the roots.

Seed trays of varying types quality can be purchased, however you get what you pay for and better quality trays can be cleaned and re-used time and time again. Clear plastic lids of various sizes can also be purchased to fit over the trays to encourage germination.

Another method is to use dried 'compost discs' that expand in water to form small, individual plugs. These are ideal as the whole plug can be planted into the soil once the plant is ready. However, they will need watering more regularly, as they are prone to dry out more quickly because the sides of the compost are exposed to the air.

Can Seeds be Sown Directly into Larger Pots?

Many readers ask the question, "why do I have to sow seeds in a seed tray and then prick them out later, why can't I sow them directly into larger pots so they won't need pricking out?". The answer is yes you can and the seedling will be very happy for it if you can provide the right conditions for germination (enough warmth, moisture and light). However, you will need to use a large number of pots, which can take up a lot of precious room in your propagator, windowsill or greenhouse so it may prove impractical.

What Compost Should be used for Seedlings?

The ideal seed compost for seed trays and pots is a standard John lnnes Seed compost mix. Because it is loam based is holds moisture well. However, there are a wide range of alternative seed composts available, many of which are now peat free. I find that it is best to experiment with different makes to find one that you like. It can be false economy to just opt for the cheapest brands when it comes to seedlings, as poor soils will cause poor germination, and damping-off can easily occur if conditions are not right. It is always a good idea to save some of the seeds from a packet (re-sealing after opening and storing in a cool dry place), so that a second sowing can be made if the first attempt fails.

Preparing Seeds for Sowing

Hard-coated seeds may need soaking first, so that moisture can penetrate the shell of the seed and start the germination process. For really tough seeds, such as sweet peas, the outer coat can benefit from being scratched or chipped to let the moisture in. A simple way of achieving this to use a jar lined with coarse sandpaper - simply pop in the seeds, replace the lid, and give the jar a good shake.

Standard Method for Sowing Seeds in Trays

The actual requirements for sowing can vary depending on the variety of seed used. The best advice is to follow the instructions on the packet each time you sow. Especially if you are sowing several packets of seeds each requiring different methods. Small seeds can simply be scattered over the surface of the compost, then dusted over with sieving of fine compost or vermiculite. Larger seeds can be pushed into the soil at regular spacings. However you should always ensure that the seeds are evenly distributed and not clumped together in one area, which will reduce the need to thin the seeding out later on. Very fine seeds can be mixed with fine sand before sowing to ensure they are evenly distributed over the surface. Not all seeds need to be covered over as some varieties need light to germinate, so check the instructions on the packet before sowing.

Once you have sown the seeds, cover the trays or pots with a cover to retain moisture and keep the temperature constant. You can use clear glass, clear polythene, cling film or a proprietary clear plastic seed tray cover. If the seed variety needs darkness to germinate then place a sheet of paper or card over the tray beneath the cover. As soon as the seeds have germinated, remove the paper/card covering, as the seedlings will then need light at this point.

Once germinated place the seedlings in good daylight. Lack of light will cause pale, spindly growth. If the light is coming from one side only, such as on a windowsill, turn the trays or pots daily, otherwise the seeds will lean over towards the light. One good idea is to place a mirror or a white reflective surface behind the seed tray to help alleviate this.

Pricking Out Seedlings

Once your seedlings produce a second set of leaves they are ready for pricking out. Do it before they get too big or the roots can get entangled and you won't be able to separate them without damage. Transfer them into individual pots or deeper seed trays, spaced a minimum of 5cm (2 in) apart in each direction. The pots or trays should contain good quality seedling compost such as John Innes No 1. First use a dibber to create a small planting hole in the pot or tray, then use a widger to lift the seedling out, with as much root intact as possible. Make sure you only handle the seedling by its first set of leaves (seedling leaves) and not by the stem. After pricking out, water lightly and leave in a lightly shaded spot for a day or two, until the seedlings become established, then return them to the full light.

Sowing Seeds Outdoors

When the weather is warm enough, and the soil too has warmed and is workable, seeds can then be sown directly into formal drills or scattered on prepared seed beds.

Seed must be sown at the correct depth. This information is usually given on the packet but, if in doubt, aim to bury the smaller seeds at a depth of approximately 1 in (13 mm), certainly no deeper.

Sowing seeds in drills (rows)

Vegetable seed are normally sowed in drills so that the correct spacing between plants is obtained, as follows:

  1. First rake the soil well to obtain a fine tilth free from large stones.
  2. Draw out a drill against a line to ensure the row will be straight.
  3. If the soil is dry then water the drill with a fine rose and let it soak in.
  4. Ensure the drill is at the correct depth required for the size of seed to be sown.
  5. When sowing fine seed sprinkle a little sparingly along the drill. Large seeds can be placed in the drill at the correct spacing.
  6. Rake the soil lightly to fill in the drill, covering the seeds with soil. Fine seeds need only a light covering.
  7. Gently firm the soil down over the drill.
  8. Label the row as soon as it has been sown.
  9. If you have planted large seeds such as peas and beans then provide a method of protecting the crop from birds over the rows.

Broadcast sowing over a large area

Broadcast sowing is usually done for annuals, wild flowers and grasses, as follows:

  1. First rake the soil well to obtain a fine tilth and ensure it is free from large stones.
  2. Scatter the seed finely and rake it gently in.
  3. Gently firm the soil down over the area.
  4. Water the area with a watering can that is fitted with a fine rose.
  5. If you have problems with birds then provide a method of protecting the seeds from above.