Plant Propagation Techniques – Sowing Seeds

Plant Propagation Techniques

There are several plant propagation techniques and this article is about the plant propagation technique of sowing seeds.


Plant Propagation

Propagating your own plants not only saves money, it also generates a tremendous sense of satisfaction. The sight of a box of newly germinated seedlings, or of a mass of healthy white roots on a cutting, is always gratifying. It’s an experience to thrill the beginner, but even the most seasoned gardener experiences a similar feeling, for there are always the more difficult species to offer a challenge.

sowing seeds Expensive equipment and a greenhouse are not necessary, though they may help with difficult species. Most will require nothing more than good compost and a warm windowledge; indeed some plants are so easy to propagate that the constant supply of offspring can be an embarrassment.


Raising Plants from Seed

The miracle of germination holds a fascination for most gardeners, and the promise in a packet of seeds needs only a little moisture, light and warmth to be unleashed (although sometimes a little shock treatment is required to break dormancy).

By following the methods described in this section, no difficulty should be experienced with the vast majority of subjects likely to be grown in the garden or home.

Seeds are still inexpensive if you calculate the cost per potential plant, so paying a few pence more for the best strains makes sense. But remember, even if you purchase seeds in hermetically sealed packets they begin ageing the moment the packet is opened, so do not attempt to save some for future sowing.


Compost for Sowing Seeds

Good compost is essential for satisfactory germination and healthy seedlings. Avoid ordinary garden soil, and buy either John Innes Seed Compost (which can be made by anyone, but is mixed to a special formula and is loam-based), or one of the proprietary peat-based seedling composts (most of these are also suitable for growing the plants on).

Soil outdoors is more difficult to control, but peat worked into the top few centimetres (inches) of the seedbed willimprove both sand and clay soils. Do not attempt to sow until a fine crumbly structure has been created.

Seed-sowing tips and techniques A heated propagator will get the plants away to an early start, although it is not essential and really only gains a few weeks on the growing season. If you have a greenhouse, it may be possible to make a small frame within the main structure, or partition a section, so that warmth and humidity can be increased.

Pelleted seeds should be used whenever possible if you find thin sowing difficult. The amount of light, food and water seedlings receive in the first few weeks can be crucial. Thickly-sown, overcrowded seedlings are a major cause of failure. The seeds’ size governs the depth of sowing.

Darkness helps the germination of most seeds, but some require light, so read the packet carefully and do not cover too deeply or keep in a dark place if light is advised. If you are not having success with a particular kind of seed, try sowing less deeply and keep in a light place.

Pre-chilling is sometimes necessary for seeds of alpine and herbaceous plants, as well as many shrubs. A satisfactory way with most seeds that need this cold period to break their dormancy is to place them between damp blotting paper and leave them in the refrigerator for about a week.

Nicking hard-coated seeds, such as morning glory (Ipomoea) and certain sweet peas (Lathyrus odoratus), with a sharp knife enables moisture to penetrate more readily. Soaking overnight before sowing also helps.


Sowing Seeds Indoors

Most seeds can be germinated satisfactorily in the home  the problem comes afterwards, when the seedlings will soon become drawn and sickly unless good all-round light is available. Seed-raising in the home is likely to be restricted by the amount of light windowledge space available for the pricked-out seedlings.

In a greenhouse, the problem is usually one of heat, and here the restraint is holding back until sufficient warmth is available for the seedlings to grow away without check.

Sowing should not be done in a rush. To assist the drainage of loam-based compost, and to prevent compost of any kind being washed through large drainage holes, broken pots or coarse gravel should be placed at the bottom of the seed box or pot.

Whether plastic or clay containers are used, they should be clean; plastic containers have the advantage of being light and easily cleaned, but wooden trays are perfectly adequate and will last for years if treated with a suitable non-toxic preservative.

Fill the container almost to the top, then gently firm down the compost with the bottom of a clean pot, or use an improvized soil firmer.

Moisten the compost before sowing, so that small seeds are not washed out before they have a chance to germinate.

Where seed is of a size that can be handled easily, space them out to eliminate the pricking-out stage. Most fine seeds can be distributed fairly evenly by gently tapping the packet, but in the case of dust-like seeds. Such as begonias and lobelias, the job will be easier if the seed is mixed with a little dry sand and sprinkled from the fingers and thumb.

If the seeds have to be covered (study the seed packet), do it evenly. A fine-mesh sieve is useful.

Gently firm the covering to make a level finish (even fine seeds that do not need covering may benefit from being pressed into the compost). If the containers are not to be placed in a propagating case, cover with a sheet of clear glass or plastic, then shade with a piece of paper until most of the seeds show signs of germination. Turn the glass daily to avoid excessive condensation.

Pricking-off should start as soon as the seedlings can be handled by the leaves, but first moisten the compost to ease the task of removing them without damage. Space the plants in new boxes or pots of compost, sufficiently far apart to prevent them becoming drawn and overcrowded by planting-out time.

Hardening-off is a crucial stage, and should always be done gradually. The best method is to use cold-frames, but if these are not available it is a case of standing the plants outside during mild weather and bringing them in at night or during cold or windy weather.


Sowing Seeds Outdoors

Seedbed preparation must be done thoroughly. Remove all weeds, and incorporate a little general fertilizer a few weeks before sowing. Break the soil down into a fine tilth, and incorporate peat if necessary.

Sowing is best done in drills taken out with a draw hoe, using a garden line to ensure straight rows. Do not sow too deeply (check with the seed packet), and be sure to water the ground well after sowing, taking care not to wash away the seeds.

Annuals are often sown broadcast, but weeding and thinning may be easier if sown in drills within irregularly shaped patches. Unless you know what the seedlings look like, weeding an area sown broadcast can be difficult until the plants are established.

Thinning should always be done early, and in two stages. Thin first to half the final distance, to allow for losses, then eventually to the correct spacing.

Thinning is a tiresome task, and thin sowing makes the job much easier. It also tends to produce better plants.

Transplanting may be necessary for biennials and perennials, which usually spend a period in a nursery bed set aside for them to mature in size. Transplant with as little root disturbance as possible, and always try to do it when the soil is moist.

  1. Seeds should always be sown in carefully prepared boxes or pots of sterilized compost. After placing crocks over the drainage holes, place a generous quantity of compost in the box and firm using the palms and fingers to bed it well down
  2. For the final levelling and firming, use a flat piece of wood with a suitable handle. Ensure that the wood is large enough to cover most of the width of the box, as this helps to avoid unevenness and produce a level surface for sowing.
  3. Most seeds should be covered with a thin layer of sifted compost, the amount of covering depending on the size of the seed. Very fine seed may not need covering at all.
  4. Although the boxes can be watered with a finerosed watering-can, even gentle force can sometimes wash out the seeds, so it is better to stand the box in a bowl of water after sowing.
  5. Large seeds, or those that resent transplanting after germination, can be sown individually in pots. Sow two or three to a pot, then thin out to the strongest seedlings if more than one germinates. This method is often used when sowing in peat pots.
  6. Reasonably large seeds can be spaced over a seed tray by holding a few in the palm of the hand and tapping it gently with the fingers of the other hand. Very fine seed is best mixed with a little sand, and sprinkled carefully between the fingers.
  7. When the seedlings are large enough to handle. They should be pricked off (transplanted) into another box. Lift only by the seed leaves and support with a suitable stick.
  8. Seeds usually germinate most successfully in a warm, humid atmosphere. This is best provided by a propagator, preferably electrically heated, but even an unheated propagator can be useful.

22. November 2010 by admin
Categories: Garden Management, Propagating Plants | Tags: , | Comments Off on Plant Propagation Techniques – Sowing Seeds


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