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Seed Starter
and Seed Germination Database From the out of print Thompson & Morgan Seed Guide

Gardener's Supply Company

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The following data is from an out of print Thompson & Morgan 'Successful Seed Raising Guide'.  You will note that gardeners who came before us did some pretty complex tasks.  This page explains the methods referred to in the Seed Germination Database.  You may need to print the Explanatory Notes section of this page out to work with it. 


All About Seeds


A seed is an embryo plant and contains within itself virtually all the materials and energy to start off a new plant. To get the most from one's seeds it is needful to understand a little about their needs, so that just the right conditions can be given for successful growth.

One of the most usual causes of failures with seed is sowing too deeply; a seed has oSowing seeds in a pot.nly enough food within itself for a limited period of growth and a tiny seed sown too deeply soon expends that energy and dies before it can reach the surface. Our seed guide therefore states the optimum depth at which each type of seed should be sown. Another common cause is watering. Seeds need a supply of moisture and air in the soil around them. Keeping the soil too wet drives out the air and the seed quickly rots, whereas insufficient water causes the tender seedling to dry out and die. We can thoroughly recommend the Polythene bag method (No. 11) which helps to overcome this problem. Watering of containers of very small seeds

Most seeds will of course only germinate between certain temperatures. Too low and the seed takes up water but cannot germinate and therefore rots, too high and growth within the seed is prevented. Fortunately most seeds are tolerant of a wide range of temperatures but it is wise to try to maintain a steady, not fluctuating temperature, at around the figure we have recommended in our guide. Once several of the seeds start to germinate the temperatures can be reduced by about 5 degrees F and ventilation and light should be given.

Some perennials and tree and shrub seeds can be very slow and erratic in germination. This may sometimes be due to seed dormancy, a condition which prevents the seed from germinating even when it is perfectly healthy and all conditions for germination are at optimum. The natural method is to sow the seeds out of doors somewhere where they will be sheltered from extremes of climate, predators, etc. and leave them until they emerge, which may be two or three seasons later. Dormancy, however, can be broken artificially and our section Nos. 12-16 deal with this.

To jump directly to the sections you are interested in, use the links below.

Hints on
Seed Raising

Special Treatment

Explanatory Notes


This section covers tips on sprouting popular, but often hard to germinate, plants.

This section describes how to treat specific types of seeds to ensure germination. This section describes each column of information in the Germination Database This section provides the best times to sow outdoors for those seeds that cannot be germinated indoors.

Hints on Seed Raising

1. Strelitzia and similar

Do not chip or mark the seed coat at all but merely remove the orange tuft and soak for up to 2 hours, or even overnight. Sow the seeds in moist sand, pressing them into the sand until only a small part of the black seed is visible and grow in a temperature of 75 degrees F in the dark and ensure that the sand always remains moist. From 7 days onwards inspect the container once a week and as soon as any bulges, roots or shoots are seen remove the germinated seed and pot up in a compost of half peat and half sand. We find that Strelitzias often produce a root without a shoot and we have also found that the young shoots and roots are susceptible to fungal attack. Therefore as soon as possible pot up and provide light and fresh air. Germination can start within 7 days and carry on for 6 months or more.

2. Palms; Banana; Coffee; Mini-Orange; Tea; Cycads and similar

All these items can take several months to germinate and are very erratic in germination. Soak for at least 2 hours in warm water before sowing. (After soaking the parchment shell on the Coffee seeds should be removed with the fingernail). Sow in Levington or Arthur Bowers [note:  a peatmoss based mixture].  Compost and place in the dark in a temperature of 75 degrees F, keeping the compost moist at all times, but not wet. Inspect regularly and occasionally dig around in the compost with a penknife. We normally sow our seeds just below the surface of the soil as we have found that sometimes they make a very vigorous root without producing a shoot at all. If you find a seed with a root then it should be excavated and potted up into a 3-4'' pot immediately when it will produce a shoot. Cycads prefer to be potted up into a compost of half sand and half peat. The Tea requires the above treatment but in a lower temperature of 60-65 degree F.

3. Clivia and similar

Sow these seeds immediately on receipt in Levington or a peat based compost, covering with a 1/2 " compost. Water and place in the dark in a temperature of 65-70'F. Germination should occur within 3 weeks.

4. Ferns (Garden and Indoor)

The fern spore needs a fine film of moisture over which to swim in order to complete the process of reproduction, therefore a good peat compost, such as Levington, ought to be used pressed down very firmly and which is a lot more moist than one would normally have it in order to provide the moisture film. The spore (seed) should be sprinkled close together on the surface of the soil and not covered and the container should be covered with a piece of glass and placed in diffused light, but not darkness. It is essential to ensure that the compost remains moist at all times. Germination which commences with the appearance of a film of green jelly over the soil can take anything from 1 -5 months.

You may wish to try germinating the fern spore on blotting paper which is placed in a saucer and kept moist at all times. A transparent cover is inverted over the saucer and the whole lot placed in a well lit but not sunny position. You can actually see the fern spores developing and when you can see small plantlets appearing along the jelly the blotting paper should be lifted and placed on the surface of a container of Levington compost and watered well. It should then be covered with a transparent cover which can remain there until the plants are quite large.

5. Bromeliads; Cineraria; Calceolaria; Insect Eaters (Drosera, Nepenthes, Sarracenias); Living Stones; Meconopsis; Rubber Plants; Saintpaulia; Streptocarpus; Tibouchina; Xmas Cactus; Begonia and similar.

These seeds should be sown on the surface of the compost and not covered. The compost should be quite moist and we would recommend that you cover the seed container with a piece of glass or clear plastic and leave in a temperature of approximately 65 degrees F in a position which receives diffused light. Once some of the seeds have germinated air should be admitted gradually otherwise the seedlings may damp off.

Alternatively the seeds can be sown on to moist blotting paper or kitchen towel placed in a saucer. Cover with a transparent cover and place on a windowsill which receives plenty of light, but not direct sunlight. Keep the blotting paper wet at all times and when the tiny seedlings are large enough to handle prick out into small pots. If the INSECT EATERS are sown using the first method described the compost requires to be both moist yet free draining. Use only pure peat with no fertiliser added to which sphagnum moss should be added if available.

6. Alstroemeria; Bonsai; Clematis; Hardy Cyclamen; Eucalyptus; Flower Lawn; Helleborus; Hosta; Primula; Iris and similar.

Sowing OCTOBER-FEBRUARY. Sow the seeds in John Innes [note:  a loam-based mixture] seed compost, covering them with a thin layer of compost. After watering place the seed container outside against a North wall or in a cold frame, making sure they are protected against mice, and leave them there until the spring. The compost should be kept moist but not wet at all times, and if the seed containers are out in the open then some shelter has to be given against excessive rain. In the spring bring the seed containers into the greenhouse, or indoors on to a well lit but not sunny windowsill and keep the compost moist. This should trigger off germination. If the seeds do not germinate in the spring keep them in cool moist conditions throughout the summer. As each seed germinates we would recommend that you transplant it almost immediately into its own pot.

Sowing MARCH-SEPTEMBER. Sow in John Innes seed compost, or something similar, and place each container in a polythene bag and put into the refrigerator (not the freezer compartment) for 2-3 weeks. After this time place the containers outside in a cold frame or plunge them up to the rims in a shady part of the garden border and cover with glass or clear plastic. Some of the seeds may germinate during the spring and summer and these should be transplanted when large enough to handle. The remainder of the seeds may lay dormant until next spring.

Germination of some items, particularly Alstroemeria, Clematis, Hardy Cyclamen and Christmas Rose (Helleborus) may take take 18 months or more.

An alternative method for growing PRIMULAS is to sow in a peat based compost which has already been moistened and do not cover the seed. Cover the container with a piece of glass or plastic and grow in the dark in a steady temperature of 60F. This is quite adequate and over 65'F germination will be inhibited. When the seeds start to germinate sprinkle a thin layer of fine compost over them and when the seed leaves come through this, move the box to a well lit place with a temperature of 55'F. At no time should the seed box be in full sun.

Hardy Cyclamen have been found to germinate best in total darkness at around 55-60'F. We have had good results with the following method. Place the seeds between two pieces of damp filter paper, Kleenex tissue, etc., then put into a polythene bag and place this into an opaque container in order to exclude all light. Inspect the seeds after a month and remove and prick out as the seedlings appear, returning the ungerminated seeds to total darkness.

7. Freesia

Soak the seeds for 24 hours and sow in Levington compost, or something similar, and place in a temperature of 50-60'F. Germination can sometimes be slow.

8. Nertera Granadensis (Bead Plant)

We recently found that this subject requires a well drained compost which is completely free from fertiliser (e.g. moss peat and sand in equal parts). Sow by barely covering the seed and place a sheet of glass over the container, and leave in a temperature of 65-75'F. Turn the glass daily as excessive condensation can kill the young seedlings. On germination the seedlings look very thin and spindly and the glass should be removed almost immediately and the seed container moved to a well lit but not sunny position. Prick out as soon as possible into a compost of 50% pure peat and 50% sand. Keep moist and shaded until established.

9. Cactus and similar

Make very shallow furrows in compost with a plant label and sow in these. No seed should be completely buried. Water from beneath and cover with glass and brown paper or black Polythene. Place in a dark position in a temperature of 70-75F and keep moist. On germinating move to a light but not sunny windowsill, give plenty of ventilation and water from beneath. Pot up when they begin to overcrowd. During the first winter only keep warm and do not allow to get too dry. If it is not possible to grow warm then keep them drier. Subsequent years keep relatively dry through the winter. Can be planted outside, plunged to the rim, all summer if required.

10. Lilies

Successful germination of seeds of some lilies requires a period of warmth followed by one of cold.

Method 1. Put seeds in a screw top jar in moist (not wet) peat and keep at 70-75F for 3-4 months. Inspect regularly, any normal seedlings (that is having root and seedling leaves) should be pricked out as they germinate. Any seeds which produce roots but not seedling leaves, sow in a pan and keep at 32-40'F for 3 months. Seed leaves and normal growth will follow.

Method 2. Sow in a pan in summer (warm spell); put in a frame (or outside covered by a piece of glass) for the winter. Seeds will germinate in spring. Soil Humus rich (peat or leaf mould) lime free and very free drainage (use 1/3 grit). Never over-water, keep bulbs almost dry from November to March.

11. For more delicate seeds

A method which has proved useful for not only small delicate seeds but for a wide range of types is the Polythene bag method.

The seeds should be sown on the surface of the moist compost, covered to their recommended depth if necessary and the container is then placed inside a Polythene bag after which the end is sealed with an elastic band. The bag should 'fog-up' with condensation within 24 hours and if this does not occur place the container almost up to its rim in moisture until the soil surface glistens, then replace in the bag and reseal. The bag is not removed and normally no more watering is required until the seeds germinate. However, it is wise, if left for a long period to check the compost occasionally.

The seed container, bag etc. should be placed in a well lit place with a steady temperature. As soon as a fair number of the seedlings emerge remove the polythene bag, lower the temperature a few degrees and provide plenty of light, but not bright sunshine, to ensure that sturdy seedlings develop. It is also helpful to spray the seedlings occasionally for the first 14 days.

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Special Treatment

12. Hard Seeds-Chipping

Some seeds, e.g. Sweet peas, lpomaea etc., have hard seed coats which prevent moisture being absorbed by the seed. All that is needed is for the outer surface to be scratched or abraded to allow water to pass through. This can be achieved by chipping the seed with a sharp knife at a part furthest away from the 'eye', by rubbing lightly with sandpaper or with very small seed pricking carefully once with a needle etc.

Some of our geranium seeds have already been treated in this way when you receive them.

13. Hard Seeds-Soaking

Soaking is beneficial in two ways; it can soften a hard seed coat and also leach out any chemical inhibitors in the seed which may prevent germination. 24 hours in water which starts off hand hot is usually sufficient. If soaking for longer the water should be changed daily. Seeds of some species (e.g. Cytisus, Caragana, Clianthus) swell up when they are soaked. If some seeds of a batch do swell within 24 hours they should be planted immediately and the remainder pricked gently with a pin and returned to soak. As each seed swells it should be removed and sown before it has time to dry out.

14. Stratification (cold treatment)

Some seeds need a period of moisture and cold after harvest before they will germinate-usually this is necessary to either allow the embryo to mature or to break dormancy. This period can be artificially stimulated by placing the moistened seed in a refrigerator for a certain period of time (usually 3- 5 weeks at around 41 F). With tiny seeds it is best to sow them on moistened compost, seal the container in a Polythene bag and leave everything in the refrigerator for the recommended period. However, larger seeds can be mixed with 2-3 times their volume of damp peat, placed direct into a Polythene bag which is sealed and placed in the refrigerator. Look at seeds from time to time. The seeds must be moist whilst being pre-chilled, but it doesn't usually benefit them to be actually in water or at temperatures below freezing.

Light also seems to be beneficial after prechilling and so pre-chilled seeds should have only the lightest covering of compost over them, if any is required, and the seed trays etc. should be in the light and not covered with brown paper etc.

15. Double Dormancy

Some seeds have a combination of dormancies and each one has to be broken in turn and in the right sequence before germination can take place; for example, some Lilies, Tree peonies, Taxus need a three month warm period (68-86'F) during which the root develops and then a three month chilling to break dormancy of the shoots, before the seedling actually emerges. Trillium needs a three month chill followed by three months of warmth and then a further three month chill before it will germinate.

16. Outdoor treatment

The above mentioned methods (12-15) accelerate the germination process and help to prevent seeds being lost due to external hazards (mice, disease, etc.) but outdoor sowing is just as effective albeit longer. The seeds are best sown in containers of free draining compost and placed in a cold frame or plunged up to their rim outdoors in a shaded part of the garden, preferably on the north side of the house avoiding cold drying winds and strong sun.

Recent tests show that much of the beneficial effects of pre-chilling are lost if the seed is not exposed to light immediately afterwards. We therefore recommend sowing the seeds very close to the surface of the soil and covering the container with a sheet of glass. An alternative method especially with larger seeds, is to sow the seed in a well prepared ground, cover with a jam jar and press this down well into the soil so that the seeds are enclosed and safe from predators, drying out etc.

We would also recommend you consult No. 6 which contains further practical suggestions regarding the special treatment of seeds.

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Explanatory Notes for other columns in the database

Germination days

The usual time period in which a particular variety will germinate given optimum conditions.


Seeds needing light should have no newspaper, brown paper etc. placed over the trays. Seeds needing dark for germination should be placed in total darkness.  Seeds with these strict requirements will have a L for light and a D for dark in that column.

Slow and irregular germination

This is the column with the "X". Not all seeds will show at once - prick out each seedling as it becomes large enough to handle and don't discard the container until well over the time suggested.


A steady temperature between these limits is recommended-fluctuating temperatures can damage a seedling in its critical early stages.


Most reputable seed composts will be quite adequate and we have indicated where a loam based type such as John Innes or a peat based type such as Levington would be slightly more suitable. On no account should potting composts, which have additional fertilisers, be used.

Sowing Depth

If in doubt sow shallowly, but always ensure that the compost surface is damp.  J.C. =Just cover the seed with compost or sharp sand. S=Sow on the surface and do not cover at all with compost.

Sowing in situ

Where recommended under the heading of comments, these seeds can be sown out of doors. Moist soil worked down to a fine tilth is essential. For hardy annuals and perennials sowing can be carried out from late winter onwards as soon as the ground is workable and has warmed up and half hardy annuals after all danger of frost is passed.

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Suggested Sowing Times

Many seeds, particularly in the house plant group, can be sown indoors at almost any season of the year. Others, for example bedding plants, have a much limited sowing season because the plants need to be at just the right stage when planted out. We therefore offer the following general guide to sowing times. Your actual time of sowing will depend a great deal upon the steady temperature you can maintain in your greenhouse/propagator, soil, local conditions etc.


Hardy Annual

Late winter/early spring


Half Hardy Annual

Spring 4-8 weeks before planting out


Greenhouse Bulb

 Sow in greenhouse


Greenhouse Shrub

 Sow in greenhouse


Greenhouse Tree 

 Sow in greenhouse


Hardy Perennial

Late winter/spring or late summer/autumn


Half Hardy Perennial

Late winter/spring


Hardy Bulb

Late winter/spring or late summer/autumn


Half Hardy Bulb 

Late winter/spring


Hardy Biennial

Late spring/early summer


Half Hardy Biennial



Hardy Shrub

Winter/late spring and late summer/autumn


Half Hardy Shrub

Any time of year


Hardy Tree

 Winter/late spring and late summer/autumn


Half Hardy Tree

Any time of year

Any plant which is to be planted outside (HA, HHA, HHP, HHSh.) should be well hardened off beforehand. This is best achieved by placing the plants outside in a cold frame for around a week before planting out. The frame can be left uncovered during mild weather but always replaced at night. Alternatively if no frame is available move the boxes outside to a sheltered spot during the day and bring indoors at night.

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Seed Germination Database

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