Sowing Seeds Indoors and Under Glass

Most vegetable seeds are sown directly in the ground, but there are two major groups that are sown in pots or trays — either in a frame or a greenhouse, or indoors.

One group comprises vegetables such as French and runner beans, which can be given an early start under glass and then planted outdoors when the danger of frost is past. They will mature several weeks earlier than crops sown outdoors.

In the other group are the seeds of more tender plants that need relatively high temperatures to germinate. These include aubergines, cucumbers, melons, peppers and tomatoes. The plants may be grown in a greenhouse or, like beans, moved outside when all danger of frost is past.

Plants of both groups are very easy to grow if you have an electrically heated propagator which produces the right temperature and humidity.


The propagator may be used in a greenhouse, so saving fuel costs because the rest of the greenhouse need not be heated, or it may be placed on a sunny window-sill in the house.

If you have no greenhouse or propagator, you can get seeds of hardy plants to germinate on a window-sill, but it is essential to pay attention to sowing times and to provide plenty of light to make sure that the seedlings are sturdy.

Seeds that need a fairly high temperature to germinate, such as cucumbers and melons, can be started in an airing cupboard, but again the timing must be right so that subsequent growth of the seedlings is not checked at any stage.

Risks of a check are minimised if you use a garden frame or cloches for hardening off, or acclimatising, plants before they are put in their positions in the garden. If you have neither, you will need to carry the plants outside on mild days and bring them in at night.

It is a waste of effort to sow seeds so early that seedlings either grow too spindly indoors to be of any use, or die in the cold outside. If sown too late they may not have time to mature, and the fruits to ripen, before autumn.

Always use fresh, sterilised compost, which can be bought from garden shops. Garden soil contains weed seeds and, possibly, fungal spores that will infect seedlings. Most garden soils have the wrong texture for use in pots and boxes, and will become caked and compacted after a short time.


Sowing and potting composts

The composts used for sowing and potting are different from the compost made from decaying vegetable matter in the garden.

Commercial seed and potting composts are formulated to give plants everything, except water, that they need for rapid growth. They have been sterilised to kill weed seeds and fungal spores, and are made of free-draining material that encourages root action and does not become waterlogged.

These composts are of two kinds — those based on loam and those with a peat base.

Loam-based composts

The best-known of these are the John Innes range, available in four grades: Seed compost, for sowing seeds; No. 1 potting compost, for seedlings moved from seed compost; No. 2, for potting on the plants; and No. 3, for growing plants such as tomatoes and aubergines to maturity.

John Innes is not a brand name. The formulae for the composts were evolved after long experiments at the John Innes Horticultural Institute, and anybody can make them up and sell them. The composts contain varying mixtures of sterilised loam, peat, sand and plant food to meet the needs of the plants at each stage of development.

Loam-based composts give a long-lasting supply of plant foods. Their disadvantage is that their principal ingredient is loam, and suitable types are now in short supply. As a result, some mixes of so-called John Innes compost are inferior. Ideally, the loam should come from the top spit of well-established pasture.

Soil-less composts

These pro- prietary products, such as Leving- ton compost, are based on peat to which plant foods have been added. They are light, clean to handle and uniform in quality. But plants left in them for more than two or three months need regular feeding with a general-purpose fertiliser.

Soil-less composts are sold in plastic bags and normally contain the right amount of moisture for sowing or planting. A compost will retain this moisture if the bag is resealed after only part of it is used.

Compost can be seen to have dried out when the surface is pale instead of dark brown.

When this occurs in the bag, tip out the contents, spread them thinly, water through a fine rose, and mix well before using or returning to the bag.

Where drying out occurs in a pot, immerse to the rim in water until air bubbles cease to rise from the compost. Treat seedlings growing in a tray by repeated light waterings from a fine rose.

Seed pans and plant pots

Plastic pans, pots and trays are all suitable for seed sowing. They can be washed easily after use and they do not harbour disease spores, which is always a risk with wooden seed boxes.


Indoors, any shape of container can be used, but in the greenhouse rectangular trays and pans are the most practical as they do not waste space on the staging. To save compost, use the smallest container that will provide you with sufficient seedlings.

More than one variety can be sown in the same container, provided the divisions between them are clearly marked and each variety is labelled. The easiest way to do this is to write the names of the varieties on plastic labels and use these as the division markers.

Plant pots are available in sizes from 2in (50 mm) to about 18in (455 mm), the measurements referring to the inside rim diameters. The most useful sizes are 3in (75 mm), for growing on seedlings, 41in (115 mm) for potting on when the roots fill the first pot, and 8-10 in. (200-255 mm) for plants grown to maturity.

Plastic pots are light, easy to clean and cheaper than clay pots. The rate of evaporation from the compost is slower, allowing less-frequent watering.

However, clay pots give excellent results, so do not discard them in favour of plastic pots. Always soak new clay pots, or any that. Have been stored indoors for some time, in water for an hour before using. Without soaking they will absorb too much moisture from the compost.

Peat pots are used differently from those made of plastic or clay. At planting time the pot is put straight into the ground with the plant in it. The compressed peat disintegrates and the roots grow through without any check.

Peat pots must be very damp when planted and the soil must be well watered if it is at all dry, otherwise, the peat will form a hard case and the roots will not be able to break through.

For the thrifty gardener, plastic yoghourt or cream cartons make excellent small plant pots.


Pots can be eliminated altogether by the use of soil blocks. These are lumps of loam-based compost in which seeds can be sown or seedlings planted. They maintain their cohesion long enough for the plants to reach planting-out size.

Another form of block is made from peat. Perhaps the most widely used is the Jiffy 7 — a large disc of highly compressed peat which contains plant foods and is enclosed in a fine-mesh net. When soaked in water it swells to a cylindrical block about 1in (40 mm) high on which a single seed is sown, or a seedling or cutting planted.

Soil blocks and peat blocks are ideal for sowing large seeds, such as those of cucumbers, and for raising seedlings on a window-sill.

05. June 2011 by admin
Categories: Fruit Growing, Gardening, Propagation, Vegetable Growing | Tags: , , | Comments Off on Sowing Seeds Indoors and Under Glass


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