Propagating Seeds FAQs

I would like to collect the seed from plants in my garden. How can I recognise the right time to do this?

Collect seed only from good plant specimens: the resultant plants may not be identical but they should at least have some desirable characteristics. Choose a dry, preferably sunny day to gather seeds contained in pods or capsules (it does not matter if fleshy fruits are wet when collected). Collect only ripe seed heads, which can be recognised by the change in colour (in most cases from green to brown). Pods and capsules should be harvested just before they open to disperse their contents. Spread them out on a sheet of paper in a warm dry place indoors to complete the ripening process. This will encourage the pods to open and release their seeds.

How do I prepare a ‘guaranteed weed-free’ seedbed outside? I would like to grow some hardy ornamental plants so that in a few years time I can extend my borders.

By far the best time to prepare a weed-free seed-bed is in the autumn. Preferably make a raised bed, to allow for better drainage, with a maximum width of 900 mm (3 ft) so that you do not need to stand on it at any time to work. Thoroughly dig the bed in autumn, adding a soil conditioner such as peat or compost in the bottom of each trench created by the spade, and let the winter frosts break the soil lumps down. In spring, rake the bed level and leave it fallow to allow any weed seeds to germinate; then spray them off with a contact herbicide containing paraquat. Continue to do this until the seedbed appears to be sterile of weeds. Before sowing, apply bonemeal at 100 g/m2 (3 oz/sq. yd); this will help root development of the young seedlings.

I want to grow an avocado plant from seed. How should I go about this?

Pierce the avocado stone with three cocktail sticks and suspend it in a jar of water so that the bottom of the seed just touches the water. If you place the jar in a propagator (or on a warm windowsill) at a temperature of 21°C (70°F) the seed should germinate within a couple of months. Once several strong roots have developed transfer it carefully to a pot of moist compost, and gradually harden the plant off so that it can be put in a well-lit, draught-free position in the house.

I have collected some pine cones. How do I extract the seeds?

If the cones are fully open the seed will already been dispersed. If they are tightly closed, put the cones in a bag and store them in a warm place (such as an airing cupboard) so that the scales will open to expose the seed. Shake the bag from time to time to separate the seeds.

I have tried growing sweet peas on several occasions, but have had little success in getting the seeds to germinate. I have heard that you should cut them with a knife, but wonder if this treatment might damage them. What is your opinion?

Sweet peas and many other seeds which have a very hard seedcoat are sometimes unable to absorb the water that is necessary to make the seedcoat swell and rupture, so that the root and shoot can emerge safely. An easy way to tackle this problem is to soak the seed for 24 hours in warm (but not hot) water to help soften the seedcoat. Alternatively, you can carefully nick the seed with a sharp knife to expose the fleshy part within. Seeds which are too small to handle in this way can be scratched by shaking them in a jar lined with sandpaper.

I have read that the fleshy fruit of some trees and shrubs requires chilling before the seed will germinate. Why is this, and how do I go about it?

Many fleshy fruits (such as holly, cotoneaster, berberis, mahonia, pyracantha, and sorbus berries) have a hard stone, within which is the seed. This stone, or seedcoat, will need a period of chilling before it becomes soft enough to absorb water and allow germination. Crush the fruit with a wooden presser to expose the seed, then add it to a 50:50 mixture of moist sand and peat. Place this in a container, stand it outdoors in an exposed position, and cover it with a piece of slate to prevent damage by mice. It may be 6 to 18 months depending on the type of fruit, before the seed is ready for sowing.

How can I tell when clematis seeds are ripe and ready for sowing?

The feathery seeds turn a silvery colour when ripe. They should be sown in March in pots filled with a sandy compost. Place them in a cold frame and keep them in the dark. Germination may take as long as 12 months, so be patient.

I have never had much luck growing Begonia semperflorens from seed. The germination results are always poor, even though I provide optimum conditions in my heated propagator. What could be the cause?

Begonias have tiny seeds and no covering is required. If they are buried it is likely that they will not germinate—and if they do shoot up they will probably damp-off before they have a chance to reach the surface.

Every year when I have completed my sowing programme, I have some seed left over. Can these be kept and used the following year or is it best always to buy fresh?

You can save seed from one year to the next provided it is kept cool and in an airtight container. One thing to note, though, is that germination results may not be as good in subsequent years. The viability of some seeds deteriorates rapidly after they have ripened to maturity: the seed is using its store of food in order to survive, so that less food will be available for the embryo at germination.

Do ferns produce seed or will I have to divide them to get more plants?

Ferns do not produce true seeds as such. They are propagated from spores which grow on the back of the leaf fronds. If a cloud of dust-like spores appears when a frond is tapped, the spores are ripe and ready for sowing. Collect a ripe frond and put it in a dry paper bag in a warm place, so that the spores are released. Prepare a pan of seed compost, then sow the spores onto the surface; do not cover them with compost. Place a sheet of glass over the pan to keep the humidity high, and maintain a temperature of about 21°C (70°F). Stand the pot in a tray of water from time to time to keep the compost evenly moist. Within six weeks a mossy-growth will be seen: this is the first stage in fern development. Keep it moist at all times and when, after a further four weeks or so, the first fronds appear, remove the glass to harden the plants off before they are pricked out in clumps into trays. Attempt to separate the individual fern plants only when they can be handled easily.

I would like to grow some bonsai forms of trees. I intend to collect my own seed in the autumn, but are there any which cannot be stored over the winter?

Yes—the ripe seeds of oak, horse-chestnut, and sweet-chestnut will usually lose their viability if they are not sown immediately they are collected.

I have poor eyesight and find sowing small seed difficult. Are there any tricks of the trade that will make it easier for me to sow thinly and evenly?

When sowing fine seed, such as begonias and lobelias, add to them a small amount of dry silver sand so that you can handle them more easily and see where you are sowing them. Shake the mixture from a paper bag on to the surface of the compost.

I have noticed that some seed is sold in pelleted form. What are the advantages of sowing this type?

Pelleted seeds are coated with a water-soluble soil-clay mixture. They make sowing much easier because they are large enough to handle individually. You can sow the exact number of seeds you require, so you waste less. Thinning the seedlings is unnecessary, so the plants can develop without checks. But before you sow pelleted seeds you must thoroughly moisten the seed bed, so that the coating will quickly disintegrate to allow germination. If the soil dries out at all it is most likely that the seeds will fail to germinate.

I would like to grow lilies from seed, but I gather that they take quite a while to germinate. Is this the case?

Lilies are best sown in the autumn, when the seed is fresh. If they are left until spring, it is probable that they will remain dormant (fail to germinate) until the following spring, when they will be chilled into action by the winter frosts.

I have some tree peony seeds. How should I sow them?

Seeds of tree peony (Paeonia lutea and P. suffruticosa) are best sown as soon as they are ripe, normally about October. Plant them 25 mm (1 in) deep and 50 mm (2 in) apart in a deep seed tray of John Innes seed compost. Water the soil from below, so as not to disturb the seeds, and place the tray in a cold greenhouse or frame. Protect the seeds from mice, otherwise you may lose them all. Frost will not harm the seed; indeed, it is beneficial. Check the seeds regularly, but it may be some months before there are any signs of germination.

As soon as the seedlings are large enough to handle, prick out the strongest directly into a well-prepared nursery bed. Plant them 300-450 mm (12-18 in) apart and leave them undisturbed for 3-4 years before planting them out in their permanent positions.

How can I prevent seedlings from damping off? Every year I seem to spend pounds on seeds which produce nothing.

Damping-off is caused by a fungus disease which thrives when conditions are far from ideal. To prevent attack, always use freshly made compost, provide optimum environmental conditions (especially good ventilation), and use water which is clean and uncontaminated. Seeds should be sown thinly and evenly, as overcrowding will encourage the disease. Other preventive measures are to water the seed trays with a solution of Cheshunt compound fungicide or use a proprietary seed dressing.

When is the best time to sow alpine plants? I understand they require a cold period. Does this mean that I will not need a heated propagator?

Most alpines should be sown when fresh because their ability to germinate deteriorates. Alternatively, they should be sown in autumn or winter in pots and kept outside to expose them to a period of cold to overcome dormancy; it may take 6-18 months. With this treatment they should germinate easily in the spring months as soon as the temperature rises.

What is fluid sowing, and is it worth trying at home?

Fluid sowing is an excellent method to use with outdoor-sown seeds, especially early in the year because they will have been given a head start. The seeds are germinated on moist tissue paper in a sealed container kept at a temperature of about 21°C (70°F). As soon as the roots and shoots emerge the seeds are collected in a sieve and rinsed before being transferred to a jelly fluid, such as wallpaper paste. The germinated seeds are carefully mixed with the paste and then sown from a piping bag into prepared drills in moist soil. Sowing is usually even, which eliminates the need for later thinning, and the plants emerge much sooner than those sown in the conventional way. Fluid sowing is, however, a fiddly method, so that it should best be used only if you have had poor results from normal sowing techniques.

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