Growing Plants From Seedlings

Growing from seed is rewarding and money saving. A few simple steps taken to provide seedlings with the best possible conditions will ensure a healthy supply of new plants. Most seedlings need some warmth, good light, careful watering and a draught-free position. If these needs are met they will flourish and grow to form healthy and bushy plants.


The best growing medium

Soil or peat-based mixtures can be used for seedlings. Many experts favour peat, which when lightly firmed is very free-draining, making it difficult to overwater. It is also well aerated if not over-compressed, and this aids good root development. Nutrients, however, are more quickly lost from peat composts and so if seedlings are very slow to mature a soil-based mixture is better. Most seedlings are moved on fairly quickly into new compost so are unlikely to be affected. Furthermore, compost requirements will vary according to the seedling’s natural habitat; plants from hot, arid conditions, for example, will be accustomed to a more sandy mixture.

The importance of good light

Pale, leggy plants will be produced where the level of light is low, so pick the brightest position you can find indoors. A bay window, giving light from three sides, will provide better light than a flat one, and dormer windows with a table beneath provide good top light, which is even better. The amount of light available to seedlings indoors can be increased by using reflectors. A large sheet of white card placed on the opposite side from the window will help to reflect light, and kitchen foil also works well. Alternatively hang a white sheet, to form a curtain behind the plants.

Covering the top of the compost with light-coloured perlite also reflects light, and natural light can be supplemented with artificial light. Use special fluorescent or mercury vapour bulbs. Ordinary household bulbs are not suitable as they convert so much energy into heat, which can easily scorch young plants.

How to water seedlings

Usually the best method of watering is to place the container in a shallow bowl filled with water and allow the mixture to take up its watering needs. Remove from the bowl as soon as the first signs of moisture appear on the surface of the compost. Alternatively, water seedlings with a fine mist sprayer.

Humidity is as important for seedlings as for older plants. Cover the container with a ventilated polythene bag and later, as seedlings develop, put pots on a tray of moist gravel. Make sure, however, that the water level in the tray does not reach the base of the plant container.


Avoiding draughts

All plants dislike draughts and the effect can be disastrous for young plants. When growing seedlings on a windowsill ensure that there is no draught. It may be necessary to seal the windows with tape. Don’t pull the curtains to trap plants in the cold space between curtain and glass, as low night-time temperatures can be fatal.

Pricking out and moving on

Seedlings need pricking out as soon as the first true leaves are large enough to handle or they will quickly grow leggy and prone to disease.

Almost fill a container with compost and then use a dibber or pencil end to make holes about 4-5cm (1 ½ -2 inches) apart for the plant roots. Hold the seedling by a leaf with the roots dangling in the hole, then lightly press the compost gently down around the stem. Seed leaves (the first that appear) should sit just above the compost surface. When all the seedlings are in place, water to settle the compost.


When plants grow so that their leaves almost touch they are ready to be transferred into individual pots. Place a layer of drainage material at the bottom then half-fill with compost. Hold the seedling in position with its roots spread out and gently dribble the rest of the potting mixture around the roots. Fill the pot, then gently firm the compost. Finally tap the pot to settle the mixture. Allow about lcm (1/2 inches) space between the top of the container and the top of the potting mixture so that there is sufficient room for watering.

  • Loosen the roots gently with a fork. It I may be easier to lift a clump of earth with each seedling, then to tease this carefully from the roots with a pencil.
  • Make small holes in the new compost about 4-5cm ( 1 ½-2 inches) apart. Holding a seedling by a true leaf, lower the roots into hole and gently firm compost.
  • Seedlings should be transplanted so that the first leaves rest just above the compost. When the tray is complete, water lightly with a mist sprayer.

Pests and diseases of seedlings

The first step to avoiding pests and diseases is to use clean containers and sterile compost but problems can still arise if the seedlings are weakened by adverse growing conditions.

Grey mould

Botrytis, commonly known as grey mould, is the only disease likely to affect seedlings and is a sign of too much damp. The seed compost should not be kept too moist, and plants need humidity and ventilation as soon as seeds sprout.

If mould appears, remove any badly affected plants, as dying vegetation is a breeding ground for the mould. Then mist spray the remaining seedlings with a fungicide containing benomyl or thiophanate methyl. Allow the compost to dry out before rewatering, and increase the ventilation.

Damping off

Damping off is an extremely common problem in seedlings which becomes manifest when young seedlings collapse. They keel over at compost level and there is no cure. Prevention can be provided by watering before seed sowing and on subsequent waterings with a solution of Cheshunt Compound.

Give seedlings the care they need and they will reward yciti with healthy plants.


Check seedlings regularly for this pest, which frequently attacks fresh young plant growth. Gently mist seedlings with a diluted insecticide.

Seedlings outdoors

If seeds are sown directly in the position where they are to flower outdoors sow the seed thinly to prevent overcrowding, which causes seedlings to become elongated and thin as they grow. Eventually seedlings will need thinning out so that each has a 2-3cm ( I inches) space of its own. Pick off the smaller, weaker seedlings and discard.

Thin as soon as the young plants have developed their first true leaves. Using finger and thumb, gently remove weaker seedlings to give others their growing space. When seedlings have increased in size again and ,Ire almost touching they will need to be thinned a second and final time. They can then be potted up into individual pots.

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