Seed germination requirements

Find below some general guidelines to help you when sowing your RHS seeds, along with specific detailed requirements for each genus

General guidelines

Getting ready
Before sowing the seed prepare all the pots. Use clean or new pots to reduce the risk of disease. A peat free proprietary seed-sowing compost usually provides excellent results. Mix up the compost to break up large lumps and to aerate it. Overfill the pot, tap the base on a surface to settle the compost, score off any excess and then lightly firm to make a smooth level surface. Leave a gap from the top of the pot depending on the size of the seed. For very small seed such as Digitalis leave a small gap of about 2mm. For larger seed such as Matthiola and Lupinus leave a larger gap of between 5–10mm. Once all the pots are filled, soak them with an upturned fine rose attached to a watering can and allow excess water to drain away.
Sowing seed
Fine Seed

Mix seed with a small quantity of fine dry sand and put in the palm of your hand. Holding your hand above the pot, gently tap your hand so the seed trickles out of your hand and is distributed evenly over the compost.

Medium Seed

You can sow seed directly from the packet, from a piece of folded paper or put some seed in the palm of your hand, pick up a pinch of seed and sprinkle the seed evenly over the compost.

Large Seed

Place each seed on the compost, sowing up to five seeds in a 9cm pot depending on seed size.

The exception is seed which resents root disturbance (where indicated in the Notes section of the germination table). You should sow these into individual pots or modules and not transplant them at the seedling stage.
 
Sow seed thinly and evenly to give each seed the air, light and moisture it needs and to minimise the risk of disease.

Covering seed
Fine Seed

There is no need to cover very small fine seed such as Digitalis, or seed that requires light for germination.

Seed germinating within 30 days

Spring is the best time of year for most seed that germinates within 30 days. Cover seed with a layer of compost to the lip of the pot. Cover to a depth of between 2–5mm depending on seed size.

Seed germinating in 60 days or longer

Seed should be covered with a 6mm layer using coarse grit.

Aftercare
Place pots in good light. A greenhouse or a cold frame is ideal and using a heated propagator in a greenhouse will speed up germination.
Overcoming dormacy

Some seeds have factors that delay germination. See Notes in germination table for details. The main barriers delaying germination are: hard or watertight seed coats; chemical inhibitors; immature embryos and cold temperature requirements. Some seeds have more than one barrier to germination that have to be overcome in a certain order. For example the hard seed coat must be penetrated to allow water to enter the seed, releasing inhibitory chemicals. This then initiates the seed to respond to a period of chilling.

Delayed Germination

Some seed may take over a year to germinate because they need more than one chilling period or treatment to break the dormancy or barriers preventing germination.

Cold moist stratification

Sow seed and place outside in an open cold frame or place into damp compost and store in the fridge for up to 12 weeks.

Chipping or softening seed coats

Hard seed coats may be softened by soaking in hot or cold water, or ‘chipped’ (nicked) with a sharp knife.

Warm stratification

This may be necessary either to break down the hard seed coat or to mature the embryo. If sowing in spring, this will happen naturally as the temperature rises. Alternatively, put the seed in damp compost and place in the airing cupboard for up to 12 weeks before sowing.

Pricking out
Germinated seedlings need good quality light to avoid becoming weak and spindly. To thin out the seedlings prick them out when the first true leaves have emerged. Prepare pots using a general peat free potting compost, creating an even, firm surface as before. Handle seedlings gently by the leaves. Use a pencil or dibber to tease out the seedlings and to make a hole in the newly prepared pot to put the seedling roots into. Fully moisten the compost carefully using an upturned fine rose on a watering can. Place the pots in good quality light.
Further information
For further advice on seed sowing we recommend looking at the RHS advice pages on seed sowing.

Specific requirements

Genus How to sow Height Sunlight
Actaea Germination may be slow, erratic, or uneven, and take up to one year. Requires a warm/cold/warm stratification cycle. Ideal temp. 22°C for 6 weeks then move to 4°C for 6–8 weeks, then return to warmth (13–16°c) for germination 0.5-1.5m Semi-shade
Agastache Sow in spring. Lightly cover seeds with seed compost. Ideal temp 10ºC–16ºC, germination 30–90 days 0.8m Full sun
Agrostemma Sow directly where they are to flower, and lightly cover with soil. Germination takes 30–90 days at 13–16°c 0.5-1m Full sun
Alcea Sow in spring. Lightly cover with a thin layer of soil. Germination can take up to 90 days at 16–21°c 1.5-2.5m Full sun
Amaranthus Sow in spring. Do not cover them with compost, the seeds need light to germinate. Germination can take up to 90 days at 21–24ºc 0.5-1.5m Full sun
Ammi Can be sown in spring or autumn into well-drained compost. Germination can be slow or erratic taking up to 21 days at 16–21°c 1m Full sun, semi-shade
Amorpha Soak in warm water for 12 hours or until seeds swell. Sow at any time of year 2mm deep. Germination should take place in 30–120 days at 10–16°c 2.5-4m Full sun, semi-shade
Amsonia Can be sown between Feb-July. Sow on the surface of the soil and gently press in, the seeds need light to germinate. Germination can take up to 90 days at 13–16°c 0.5-0.8m Full sun, semi-shade
Anemanthele Sow in spring or autumn. Cover very lightly with compost. Germination in 30-90 days at 18–21°c 1.5m Full sun, semi-shade
Anemone Sow in spring or autumn. Lightly cover the seeds with compost. Require a period of cold, moist stratification. Germination can take up to one year at 10–15°c 0.5-1m Full sun, semi-shade
Angelica Sow in spring or autumn. Can be direct sown. Lightly cover the seeds with compost, as they require light to germinate. Germination in 30–90 days at 10–15°c 1.5-2.5 Full sun, semi-shade
Armeria Sow in spring or autumn. Pre-soak the seeds in warm water overnight before sowing. Lightly cover the seeds with compost. Germination in 30–90 days at 15–20°c 0.1-0.5m Full sun
Aruncus Sow in autumn. Require a period of cold, moist stratification. Germination can be erratic and may take up to one year at 13–18°c 1.2m Semi-shade
Asphodeline Sow seeds at any time covering them very thinly with compost, seeds require light to germinate. Can be direct sown. Species resents root disturbance. Germination in 30–90 days at 15–20°c 1-1.5 Full sun
Asphodelus Sow seeds at any time covering them very thinly with compost, seeds require light to germinate. Can be direct sown. Species resents root disturbance. Germination in 30–90 days at 15–20°c 0.5-1m Full sun
Atriplex Sow in spring, lightly covering seeds. Can be direct sown outdoors onto prepared soil. Germination in 30 days at 15°c 1-1.5m Full sun
Baptisia Requires a very free draining soil. Pre-soak seeds in hot water for 12 hours. Germination can be erratic. Germination in 30 days at 20°c 1.2m Full sun
Berkheya Lightly cover seeds as require light to germinate. Germination in 90 days at 15–20°c 75cm Full sun
Betonica Sow in the autumn as require a period of cold moist stratification. Germination in 90 days at 15°c 0.6m Full sun, semi-shade
Briza Direct sow where they are to grow from early spring in any well-drained soil. Sow seeds thinly over the soil, lightly covering. Germination in 30–90 days at 10–15°c 0.6m Full sun
Butia This is very challenging to germinate. Pre-soak seeds for 10 days. Then bury the seed in perlite. Germination is erratic but may occur in 60 days at 30°c 4-8m Full sun
Calamagrostis Surface sow, lightly covering with compost. Germination within 30 days at 20°c 1-1.5m Full sun, semi-shade
Calendula Can be direct sown in spring or autumn. Germination within 30 days at 15°c 0.1-0.5m Full sun, semi-shade
Camassia Sow in the autumn, lightly covering seeds. Require a period of cold moist stratification. Germination in 90 days at 10–15°c 1m Full sun, semi-shade
Campanula Surface sow as require light to germinate. Germination in 90 days at 15–20°c 1.2m Full sun, semi-shade
Campsis Can be slow and erratic to germinate. Sow in the autumn as seeds require a period of cold moist stratification, then give extra warmth in the spring. Germination in 90 days at 15–20°c 10m Full sun
Catalpa Soak seeds for 24 hours before sowing, then surface sow as require light to germinate. Germination in 30 days at 15°c 12m Full sun
Cenolophium Sow in the autumn as require a period of cold moist stratification. Very lightly cover with compost as light is needed for germination. Germination can take up to one year at 15–20°c 0.6-1.5m Full sun, semi-shade
Centaurea Direct sow where they are to grow from early spring in any well-drained soil. Sow seeds thinly over the soil, lightly covering. Germination in 30 days at 10–15°c 0.75m Full sun
Cephalaria Sow in spring, lightly covering seeds. Germination within 90 days at 15°c 1.5-2.5m Full sun, semi-shade
Chelone Sow in spring, lightly covering with compost. Require good drainage. Germination within 90 days at 15°c 0.5-1m Full sun, semi-shade
Cichorium Sow in spring, lightly covering with compost. Germination within 30 days at 10–15°c 1-1.5 Full sun
Cistus Sow in late summer or early spring, lightly covering with compost. Germination in 90 days at 15°c 1.5-2.5m Full sun
Cordyline Sow 2mm deep in late spring. Do not overwater as seeds are susceptible to damping off. Germination within 90 days at 20°c 10-20m Full sun, semi-shade
Coreopsis Direct sow where they are to grow from early spring in any well-drained soil. Sow seeds thinly over the soil, lightly covering. Germination in 30 days at 15–20°c 1m Full sun
Cosmos Sow in spring, lightly covering with compost. Germination within 30 days at 15–20°c 1.5m Full sun
Crocus Sow in autumn as require a period of cold moist stratification. Species resents root disturbance so sow directly into suitable container. Germination up to one year at 10–15°c 0.1-0.15m Full sun
Cyclamen Sow in autumn, as require a period of cold moist stratification. Pre-soak seeds in cold water. May need two chilling periods to break dormancy. Germination up to one year at 10–15°c 0.1m Semi-shade
Datisca Surface sow as require light to germinate. Germination may be slow and erratic. Germination within 30 days at 18°c 1.5-2.5m Full sun, semi-shade
Daucus Direct sow where they are to grow from early spring in any well-drained soil. Sow seeds thinly over the soil, lightly covering. Germination in 30 days at 10–15°c 0.5-1m Full sun
Deschampsia Sow in spring, lightly covering with compost. Germination within 30 days at 20°c 1-1.5m Full sun, semi-shade
Dianthus Sow in spring, lightly covering with compost. Needs good drainage. Germination within 90 days at 15–20°c 0.1-0.5m Full sun
Dierama Sow in spring or autumn. Require good drainage. Cover to twice the seed's depth with compost. Germination may be slow and erratic and can take up to one year, at 20°c 1.5m Full sun
Digitalis Surface sow seeds in spring or summer as they need light to germinate. Germination in 30-90 days at 15°c 0.5-2m Full sun, semi-shade, full shade
Dipsacus Best direct sown in spring. Lightly cover seeds. Germination in 30 days at 20°c 3m Full sun, semi-shade
Dryas Sow in autumn, lightly covering seeds. Require a period of cold moist stratification. Germination can be very slow, up to 6 months. Temp 15–20°c 0.15m Full sun, semi-shade
Eccremocarpus Lightly cover seeds. Germination can be erratic. Germination within 90 days at 20°c 2.5-4m Full sun
Echinacea Sow seeds in autumn as they need a period of cold moist stratification. Germination within 90 days at 18–24°c 1-1.5m Full sun
Eragrostis Surface sow seeds, keeping the compost moist and humidity high. Germination in 30 days at 20–22°c 1-1.5m Full sun
Eranthis Sow seeds in autumn as they need a period of cold moist stratification. Germination can be slow and erratic, within 90 days between 5–12°c 0.15 Full sun, semi-shade
Erigeron Leave seeds uncovered when sown. Is very good at self-sowing once established. Germination in 30 days at 15–20°c 0.15m Full sun
Erodium Sow in spring or autumn, just covering seeds as light is required for germination. Germination in 30 days at 15–20°c 0.1-0.5m Full sun
Eryngium Moisten seed and place on a piece of kitchen roll and then place in a sealed plastic bag. Seed will germinate in 30 days at 15°c 0.5-2.5m Full sun
Eschscholzia Direct sow where they are to grow from early spring in any well-drained soil. Sow seeds thinly over the soil, lightly covering. Germination in 90 days at 15–20°c 0.3m Full sun
Euphorbia Lightly cover seed. Germination can be erratic, but generally takes place in 30 days at 18–24°c 1m Full sun
Eurybia Surface sow as seed need light to germinate. Require a period of cold moist stratification. Germination in 90 days at 15–18°c 0.5-1m Full sun, semi-shade
Ferula Sow in the autumn as require a period of cold moist stratification. Very lightly cover with compost as light is needed for germination. Germination can take up to one year. After chilling raise temp to 15–20°c 2.5-4m Full sun
Foeniculum It may help to soak seeds for a day before sowing. Sow in late spring. Germination in 30 days at 13–18°c 1.5-2.5 Full sun
Francoa Sow from late winter through to June, lightly covering seeds. Germination in 30 days at 13–16°c 0.5-1m Full sun, semi-shade
Geum Sow in spring, lightly covering seeds. Germination within 90 days at 13–18°c. 0.1-0.5m Full sun, semi-shade
Gillenia Sow in autumn. Require a period of cold, moist stratification. Germination within 30–90 days at 15–18°c 0.5-1m Semi-shade
Glebionis Can be sown indoors in spring, or directly outdoors slightly later. Germination in 10–14 days at 16–21°c 0.5-1m Full sun
Glycyrrhiza Pre-soak in cold water for 24 hours before sowing in spring. Germination within 30–90 days at 15–18°c 1-1.5m Semi-shade
Haplocarpha Sow in spring, lightly covering the seeds. Germination within 30–90 days at 18–20°c 0.5m Full sun
Helleborus Sow in autumn. Require period of cold, moist stratification. Germination can take up to one year at 16–18°c 0.1-0.5m Full sun, semi-shade
Hesperis Sow in the spring, lightly covering the seeds. Germination in 30 days at 18–21°c 0.9m Full sun, semi-shade
Hibiscus Soak seed for several hours in hot water before sowing. Lightly cover seeds with compost. Germination can be erratic. Germination in 90 days at 20°c 3m Full sun
Hosta Sow in spring, lightly covering seeds. Germination in 90 days at 10–16°c 0.5-1m Semi-shade
Hyacinthoides Sow in autumn, lightly covering seeds. Require a period of cold moist stratification. Germination up to one year at 10–16°c 0.5m Semi-shade
Hydrangea Surface sow seeds in spring. Germination in more than 90 days at 13–16°c 0.5m-4m Semi-shade, full shade, full sun
Indigofera Soak seeds in warm water for 24 hours before sowing, then cover with 5mm compost. Germination can be erratic. Germination within 90 days at 15–20°c 1.5-2.5m Full sun
Ipomoea Pre-soak in cold water for a few hours before sowing. Chipping seed will help with germination. Use well-drained compost. Germination within 90 days at 18–24°c 4-8m Full sun
Iris Sow in autumn. Require a period of cold moist stratification. Germination up to one year at 13–18°c 1.2m Full sun, semi-shade
Knautia Sow in autumn as seeds require cold moist stratification. Surface sow, barely covering with grit. Keep moist. Germination can be erratic and take many months. Germination in 90 days at 10–16°c 0.5-1m Full sun
Lavandula Sow in autumn, lightly covering seeds. Require a period of cold moist stratification. Germination in 90 days at 13–18°c 0.1-0.5m Full sun
Lepechinia Sow in spring, lightly covering seeds. Germination in 90 days at 15–20°c 1-1.5m Full sun
Levisticum Sow in spring, covering with approx 6mm compost. Germination in 30–90 days at 13–18°c 1.5-2.5m Full sun
Libertia Sow in autumn, lightly covering seeds with compost or grit. Require a period of cold moist stratification. Germination up to one year at 15–20°c 1m Full sun
Lilium Surface sow and cover with lime-free grit. Best sown in summer as needs warm stratification for 4 weeks, followed by a period of cold moist stratification. Germination may take up to one year at 15–20°c 1-2m Full sun
Liriodendron Sow in the autumn as require a period of cold moist stratification. Germination in 90 days at 10–15°c 25m Full sun, semi-shade
Lobelia Surface sow seeds, keeping the compost moist. Germination in 90 days at 15–20°c 0.5-1m Full sun, semi-shade
Lunaria Sow in summer, covering seeds with 3mm of compost. Germination may be slow and erratic and seeds may need a period of cold, moist stratification. Germination in 90 days at 15–20°c 0.6-0.9m full sun, semi-shade
Lupinus Soak seeds in hot water for 1–3 days before sowing. Alternatively chip seed. Then sow covering with a 5mm depth of compost. Germination in 90 days at 13–18°c 0.5-1.5m Full sun, semi-shade
Luzula Sow in spring, lightly covering with compost. Germination in 90 days at 15–20°c 0.6m Semi-shade, full shade
Lysimachia Sow seeds in the autumn covering with a thin layer of gravel. Require a period of cold moist stratification. Germination can be erratic. Germination in 90 days at 13–18°c 0.5-1m Full sun
Lythrum Sow in spring or autumn, lightly covering seeds. Can be direct sown into prepared soil. Germination in 30 days at 15–20°c 1.2m Full sun
Maianthemum Sow in summer, lightly covering seeds with compost. Seeds need a period of warm stratification followed by a period of cold moist stratification. Germination up to one year at 10–15°c 0.5-1m Full shade, semi-shade
Melanoselinum Sow in autumn. Require a period of cold, moist stratification to germinate. Cover with a thin layer of grit and leave somewhere sheltered. Germination up to one year at 16–21°c 1.5-2.5m Full sun, semi-shade
Miscanthus Sow in spring, surface sowing the seed. If results are poor try a period of cold, moist stratification. Germination in 90 days at 15–20°c 1.5-2m Full sun
Molinia Sow in autumn, lightly covering seeds. Require a period of cold, moist stratification. Germination within 6 months at 10–15°c 1-1.5m Full sun, semi-shade
Muscari Sow in the autumn. Pre-soak in cold water then lightly cover with grit. As species resents root disturbance sow directly into suitable container. Germination up to one year at 10–15°c 0.1-0.5m Full sun, semi-shade
Myrrhis Sow in the autumn as require a period of cold moist stratification. Germination may be slow or erratic. Germination within 6 months at 15–20°c 1-1.5m Semi-shade
Nepeta Sow in spring or autumn, lightly covering seeds. Germination in 90 days at 15–20°c 1.5-2m Full sun
Nicandra Sow in spring, lightly covering seeds. Germination within 90 days at 15–24°c 0.9m Full sun, semi-shade
Nigella Sow in spring or autumn, lightly covering seeds. Can be sown direct outside, where to flower. Germination within 90 days at 13–18°c 0.5-1m Full sun
Oenothera Sow in spring, lightly covering seeds. Germination within 30 days at 18–20°c 0.9-1.5m Full sun
Panicum Sow in spring, lightly covering seeds. Germination may take up to 6 month at 16–21°c 0.5-1m Full sun
Papaver Best sown direct, lightly cover seeds. Germination in up to 90 days at 13–18°c 0.6-1.2m Full sun, semi-shade
Paulownia Surface sow as require light to germinate. Germination in up to 90 days at 16–18°c 8-12m Full sun
Pennisetum Sow in spring, in well-draining compost. Germination in up to 30 days at 18~21°c 0.1-1.5m Full sun
Phacelia Suitable for sowing direct outside between March and September. Germination in up to 30 days at 10–16°c 0.5-1m Full sun
Phlomis Sow in autumn or late winter, lightly covering the seeds. Germination may take up to 6 months at 16-21°c 0.9m Full sun
Potentilla Sow in autumn, lightly covering seeds. Require a period of cold, moist stratification. Germination in 30–90 days at 18–21°c 0.5-1m Full sun
Primula Leave seeds uncovered when sown. Require a period of cold moist stratification. Germination in up to 90 days, at 13–16°c 0.5-1.5m Full sun, semi-shade
Pulsatilla Lightly cover the seeds. Require a period of cold, moist stratification. Germination can take up to one year, at 13–16°c 0.1-0.5m Full sun
Rudbeckia Lightly cover the seeds. If germination is poor, cold stratify for 4 weeks. Germination in up to 30 days, at 16–18°c 0.5-2.5m Full sun, semi-shade
Salvia Sow in spring and leave seeds uncovered when sown. Germination in up to 30 days at 18–24°c 0.1-1m Full sun
Sanguisorba Sow in autumn. Does not like root disturbance. Can be direct sown, or indoors preferably in modules, lightly covering seeds with compost. Require a period of cold moist stratification. Germination in up to 3 months at 15–20°c 1.5-2.5m Full sun, semi-shade
Scabiosa Sow in spring, lightly covering seeds. Germination can be erratic, and take up to 90 days at 16–21°c 0.5m Full sun
Silene Direct sow in prepared soil in early spring or autumn, lightly cover seeds. Germination in up to 30 days at 16–21°c 0.75-1m Full sun, semi-shade
Sisyrinchium Lightly cover seeds. Germination can be slow and erratic, taking up to one year at 13–18°c 0.45-1m Full sun
Spartium Sow in spring, soaking seeds in warm water for 12 hours before sowing shallowly. Germination in up to 90 days at 13–18°c 1.5-2.5m Full sun
Sporobolus Sow indoors from autumn to early spring. Germination within 30 days at 15–20°c 0.5-1m Full sun
Stachys Sow in spring, lightly covering seeds. Germination in 30–90 days at 18–21°c 0.6m Full sun
Stipa Sow in spring. Germination in 30–90 days at 18–21°c 60cm Full sun
Succisa Lightly cover seeds. Germination can be slow and erratic, taking up to 90 days at 18–21°c 0.5-1m Full sun, semi-shade
Tellima Sow in autumn or spring, lightly covering the seeds. Germination can take more than 90 days at 16–21°c 0.75m Full sun, semi-shade, full shade
Teucrium Sow in spring, lightly covering seeds. Germination can take up to 30 days at 16–21°c 0.6m Full sun
Thalictrum Sow in autumn, covering lightly with grit. Require a period of cold, moist stratification. Germination within 30 days at 13–18°c 1-1.5m Full sun, semi-shade
Tigridia Species resents root disturbance, sow directly outdoors or indoors in modules. Germination can take up to one year at 21–27°c 1-1.5m Full sun
Trachycarpus Pre-soak in cold water for a few days. Require a period of cold moist stratification. Germination can take up to one year at 25–28°c 12m Full sun, semi-shade
Tricyrtis Surface sow in autumn, needs light to germinate. Require period of cold, moist stratification. Germination can be slow and erratic, taking up to 90 days at 13–18°c 0.5-1m Full shade, semi-shade
Trifolium Sow in spring, lightly covering seeds. Germination in 30 days at 18–21°c 0.45m Full sun, semi-shade
Valeriana Surface sow in spring, require light to germinate. Germination in 30 days at 15–18°c 1-1.5m Full sun, semi-shade
Verbascum Sow in spring, lightly covering seeds. Germination in up to 30 days at 15–18°c 0.5-1m Full sun
Verbena Lightly cover seeds, germination can be slow and erratic. Germination in 90 days at 18–21°c 1-2m Full sun
Veronica Surface sow seeds, leave uncovered as require light to germinate. Germination in 90 days at 13–18°c 0.5-1.5m Full sun
Veronicastrum Surface sow seeds, leave uncovered as require light to germinate. Germination in 90 days at 16–21°c 1.2m Full sun, semi-shade
Viburnum Warm stratify for 4 weeks, then cold stratify for 4 weeks. Chilling may improve germination. Germination can take up to one year at 18–21°c 1.5-2.5m Full sun, semi-shade
Watsonia Species resents root disturbance, sow directly outdoors or indoors in modules, covering lightly. Germination can take up to one year at 10–16°c 0.5-1m Full sun
Xerochrysum Sow indoors from March or direct sow outdoors from May. Cover lightly. Germination in 30 days at 16–20°c 0.5-1m Full sun

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