Reference
Which Seeds Need Light to Germinate, and Which Need Darkness
Dormancy gets the blame for most empty trays. Sowing depth deserves more of it. Here is which way round each of 78 common garden plants wants it.
By Sohail Akhtar · September 2026
Why this matters more than dormancy
A seed that needed light and got buried does not come up. Neither does a seed that needed a cold period and never had one. From the outside the two failures are identical — a tray of compost with nothing in it — and the internet will tell you it was dormancy, because dormancy is the more interesting answer.
It often is not. Of the 78 plants in our cold stratification reference, only 21 genuinely need a cold period, while 24 need light on the seed and 7 need to be covered. Depth decides more trays than dormancy does, and unlike dormancy you can get it wrong in either direction.
Yarrow and calendula are the pair worth remembering, because they fail in opposite directions. Yarrow must sit on the surface. Calendula must be covered about 6mm deep. Sow them the same way on the same afternoon and one of them will not come up.
Seeds that need light — surface sow (24)
These will not germinate reliably in the dark. Press them onto the surface and do not cover them. The cold column tells you whether the species has a dormancy requirement as well, because several here need both and missing either one produces the same empty tray.
| Plant | Cold too? | What to know |
|---|---|---|
| Swamp milkweed Asclepias incarnata | Yes, 4 wks | Same thirty days as common milkweed. It wants damper ground afterwards than the other asclepias, which is the part people miss. |
| Columbine Aquilegia spp. | Yes, 3–4 wks | Needs light as well as cold, so surface sow after the cold period rather than burying it. |
| Anise hyssop Agastache foeniculum | Yes, 4 wks | Surface sow after stratifying — it needs light to germinate, so the cold period and the sowing depth are two separate requirements. |
| Bee balm / wild bergamot Monarda spp. | Yes, 4 wks | Both the garden bee balm and wild bergamot want the same month of cold. Surface sow afterwards; the seed is tiny and needs light. |
| Blue vervain Verbena hastata | Yes, 4 wks | Not the same plant as the garden verbena further down this list, and unlike it, this one will not germinate at all without the cold. It needs light afterwards too — surface sow it. |
| Black-eyed Susan / rudbeckia Rudbeckia hirta | Optional | Germinates without cold, but a month of it makes the tray come up evenly instead of over three straggling weeks. It also needs light, so do not bury it. |
| Blanket flower Gaillardia spp. | Optional | Surface sow either way — it needs light, and that matters more than the cold period does. |
| Coreopsis Coreopsis spp. | Optional | Perennial coreopsis responds to cold more than the annual types do. Both need light to germinate. |
| Foxglove Digitalis purpurea | Optional | Dust-fine seed that must sit on the surface in good light. Every part of the plant is toxic — worth knowing before you put it where children or livestock go. |
| Canterbury bells Campanula medium | Optional | Biennial — a rosette in year one and flowers in year two, whatever you do about stratification. Surface sow; it needs light. |
| Cleome (spider flower) Cleome hassleriana | Optional | A brief chill, or fluctuating day and night temperatures, both break its light dormancy. It needs light too. |
| Snapdragon Antirrhinum majus | No | A light problem, not a cold one. Surface sow and keep it bright and cool. Sowing it at refrigerator temperature only slows it down. |
| Evening primrose Oenothera biennis Full guide | Optional | Direct sown in autumn, the winter does this for you. Biennial, so year one is a leaf rosette and year two is flowers. |
| Yarrow Achillea millefolium Full guide | No | Needs light, not cold. Surface sow and never bury it — burying yarrow is the usual reason a tray comes up empty and gets blamed on dormancy. |
| German chamomile Matricaria chamomilla Full guide | No | Surface sow for light. Roman chamomile behaves the same way — neither wants a cold period. |
| Feverfew Tanacetum parthenium Full guide | No | Germinates readily at room temperature. It needs light, so press it onto the surface rather than covering it. |
| Petunia Petunia × atkinsiana | No | Dust-fine seed that needs light and warmth. Surface sow and do not let it dry out. |
| Sweet alyssum Lobularia maritima | No | Surface sow for light. Germinates in under a week at room temperature and self-seeds thereafter. |
| Strawflower Xerochrysum bracteatum | No | Needs light to germinate. Surface sow into warm compost after the last frost. |
| Dill Anethum graveolens | No | Direct sow for the taproot and give it light; dill germinates better uncovered. |
| Oregano Origanum vulgare | No | Tiny seed that needs light. Surface sow and keep it warm. |
| Thyme (and creeping thyme) Thymus spp. | No | Needs light. Surface sow it, keep it warm, and be patient — two to three weeks is normal. |
| Lemon balm Melissa officinalis | No | Needs light, so surface sow. It spreads hard once established — a container is worth considering. |
| Bellflower Campanula spp. | No | Most of the genus needs no cold, but it is a big genus and a few do. Surface sow — the seed is fine and wants light. |
Seeds that need darkness — cover them (7)
The opposite problem, and a smaller group. Left on the surface these germinate poorly, so cover them properly rather than dusting compost over the top.
| Plant | Cold too? | What to know |
|---|---|---|
| Delphinium Delphinium spp. | Yes, 2–4 wks | Also wants darkness and cool soil to germinate. Fresh seed performs far better than old — delphinium loses viability quickly at room temperature. |
| Larkspur Consolida ajacis | Yes, 1–2 wks | Cold and darkness together. Autumn direct sowing is easier than the refrigerator for this one, because larkspur hates root disturbance. |
| Bachelor's buttons (cornflower) Centaurea cyanus | No | Needs darkness rather than cold, so cover the seed. Direct sows happily in autumn or early spring. |
| Calendula Calendula officinalis Full guide | No | The opposite requirement to yarrow: it needs darkness, so sow it about 6mm deep. No cold treatment at all. |
| Pansy / viola Viola × wittrockiana | No | Wants darkness and cool — not cold — soil to germinate. Cover the seed and keep it around 18°C. |
| Verbena Verbena spp. | No | Needs darkness and patience — germination is slow and uneven, but cold does not fix it. |
| Borage Borago officinalis | No | Direct sow and cover — it wants darkness. Self-seeds enthusiastically forever after. |
Seeds with no strong preference (47)
No documented preference strong enough to change how you sow them. Use the ordinary depth rule and spend your attention on temperature and moisture instead, which is what these actually respond to.
Where a species is listed here it means we found no clear requirement, not that we found a proof of indifference. If a packet for one of these says surface sow, follow the packet.
| Plant | What to know |
|---|---|
| Milkweed (common) Asclepias syriaca | Thirty days in the refrigerator is the single biggest lever on milkweed germination. Winter sowing outdoors in a vented container does the same job and is what most monarch programmes recommend. |
| Butterfly weed Asclepias tuberosa | The taproot resents disturbance, so stratify and then direct sow, or start in deep cells and transplant early. |
| Echinacea (purple coneflower) Echinacea purpurea Full guide | Germinates patchily in warm soil and reliably after four cold weeks. This is the species most often blamed on bad seed when the problem was dormancy. |
| Lavender Lavandula angustifolia Full guide | Even stratified, lavender is slow and low-percentage from seed. Sow more than you need and expect three weeks to a month before anything shows. |
| Aster (perennial) Symphyotrichum spp. | Perennial asters need the cold period. Annual China aster (Callistephus) does not, and the two get confused constantly. |
| Marshmallow root Althaea officinalis Full guide | Erratic without the cold period, and it wants genuinely damp ground afterwards rather than the sharp drainage most herbs prefer. |
| Hosta Hosta spp. | Seed-grown hosta does not come true to the parent plant. If you want a named variety, divide it instead of sowing. |
| Apple Malus domestica | Seedlings will not resemble the fruit you took the pips from — apples do not come true from seed. Grow them for rootstock or curiosity, not for the same apple. |
| Peach Prunus persica | Crack the hard outer stone carefully and stratify the kernel inside to cut the wait considerably. |
| Cherry Prunus avium | The longest wait on this list. Start in autumn so the period finishes in time for a spring sowing. |
| Blueberry Vaccinium spp. | Needs acidic growing medium after stratification, and several years to fruit. Named cultivars are far faster bought as plants. |
| Joe Pye weed Eutrochium purpureum | One of the few daisy-family plants that genuinely needs the cold period — most of that family does not, which is why this one catches people out. |
| Ironweed Vernonia noveboracensis | Tall, late and worth the wait, but it will not shortcut the cold. Sow it in autumn outdoors if the refrigerator is full. |
| Penstemon Penstemon spp. | The western mountain species are the strict ones. Short-lived species that flower in their first year are much more relaxed about it. |
| Shasta daisy Leucanthemum × superbum | Will germinate warm. Cold mainly tightens up how evenly the tray comes through. |
| Poppy Papaver spp. | A short chill helps, but autumn or late-winter direct sowing does the same job with no refrigerator. Poppies resent transplanting, so sow where they are to flower. |
| Scabiosa (pincushion flower) Scabiosa spp. | Perennial scabiosa benefits; the annual types germinate readily warm with no cold at all. |
| Forget-me-not Myosotis spp. | Self-seeds so freely once established that most gardeners never stratify it twice. |
| Strawberry Fragaria × ananassa | Cold improves an otherwise slow, uneven germination. Seed-grown plants will not match a named cultivar; runners will. |
| Lupine Lupinus spp. | The barrier is a hard, water-impervious seed coat, not dormancy — so nick it with a file or soak it overnight. Chilling an unscarified lupine seed does nothing, which is why it disappoints so many people who followed a stratification list. |
| Hardy hibiscus Hibiscus moscheutos | The hard coat matters more than the cold. Nick or soak the seed first. Tropical hibiscus needs neither treatment. |
| Hyssop Hyssopus officinalis | Germinates warm without help. A short cold period evens it out. Do not confuse it with anise hyssop, which genuinely needs the month. |
| Goldenrod Solidago spp. | The answer changes with the age of your seed. Fresh autumn-collected seed wants the cold period; the same seed after a few months in a dry drawer often does not. |
| Zinnia Zinnia elegans | A warm-season annual with no dormancy at all. It wants warm soil, not cold seed — sow after your last frost and it is up in under a week. |
| Marigold Tagetes spp. | Germinates in a few days at room temperature. Chilling it wastes a month and gains nothing. |
| Cosmos Cosmos bipinnatus | No dormancy. Rich soil gives you tall leafy plants and few flowers, so sow it somewhere poor. |
| Sunflower Helianthus annuus | Direct sow after frost. The real threat is birds and mice taking the seed, not dormancy. |
| Hollyhock Alcea rosea | Commonly assumed to need cold because it is a cottage-garden biennial, but it germinates readily at ordinary room temperature in one to two weeks. Sow shallowly and keep it warm. |
| California poppy Eschscholzia californica Full guide | Direct sow only — it forms a taproot and dies if transplanted. Cool soil suits it, but that is a sowing date, not a stratification requirement. |
| Chicory Cichorium intybus Full guide | Direct sow for the taproot. Check your local weed list first — chicory has naturalised widely. |
| Nasturtium Tropaeolum majus | Soak the large seed overnight instead. Poor soil gives more flowers and fewer leaves. |
| Morning glory Ipomoea spp. | A hard seed coat, not dormancy. Nick it with a file or soak it overnight and it comes up fast. |
| Sweet pea Lathyrus odoratus | Another coat problem mistaken for dormancy. Soak or nick the seed. Autumn sowing under cover gives stronger plants, but that is a head start, not stratification. |
| Celosia Celosia argentea | A heat lover. Sow into warm soil after frost; cold treatment only delays it. |
| Gomphrena (globe amaranth) Gomphrena globosa | Warm-season annual. Soaking the fluffy seed overnight helps more than any cold period would. |
| Dahlia (from seed) Dahlia spp. | Seed-grown dahlias germinate warm in about a week and will not come true to a named parent. Tubers do. |
| Tomato Solanum lycopersicum | Wants heat, around 21–27°C. Cold seed is the opposite of what it needs. |
| Basil Ocimum basilicum | One of the most cold-sensitive things in the garden at every stage. Sow warm, plant out late. |
| Cilantro / coriander Coriandrum sativum | Direct sow — it bolts if root-disturbed. Crushing the round husk into two halves speeds germination. |
| Parsley Petroselinum crispum | Famously slow — three to four weeks is normal and gets mistaken for dormancy. Soaking overnight helps; cold does not. |
| Sage Salvia officinalis | Germinates warm in one to three weeks. Some ornamental salvias do want cold — culinary sage does not. |
| Rosemary Salvia rosmarinus | Slow and low-percentage from seed, but cold is not the fix. Cuttings root easily and are how most people propagate it. |
| Chives Allium schoenoprasum | Germinates warm in one to two weeks. Use fresh seed — allium seed loses viability faster than most. |
| Blazing star Liatris spicata | Widely sold as a seed that needs chilling. It does not — though the corms are so cheap that most people never sow it from seed at all. |
| False indigo Baptisia australis | This one appears on extension lists as requiring stratification, which is worth knowing about before you spend a month on it. Deep taproot, so sow it where it will stay. |
| Dianthus / sweet William Dianthus spp. | Reliable warm, and one of the easier perennials to raise from seed. Sweet William is a biennial, so expect the flowers in its second year. |
| Love-in-a-mist Nigella damascena | A hardy annual that resents root disturbance, so direct sow it where it is to flower. Autumn sowing gives bigger plants than a spring start. |
How to sow seed you cannot cover
Surface sowing has one real difficulty: the surface is exactly where compost dries out first, and fine seed sitting on dry compost does nothing. Four things fix it.
- Firm the compost before sowing. Seed lying in a loose, fluffy surface makes poor contact and dries faster.
- Press, do not sprinkle and hope. A flat hand or a piece of card pressed gently over the seed puts it in contact with the compost without burying it.
- Water from below. Stand the tray in shallow water until the surface darkens. Watering from above washes fine seed out of position and into the corners.
- Cover the tray, not the seed. A clear lid, propagator top or even a freezer bag holds humidity at the surface while still letting light through. Take it off once germination starts.
The same four apply to the light-requiring species that also need a cold period — stratify first, then surface sow. The two requirements are independent, and winter sowing handles both at once for the outdoor species, since a vented jug gives them cold, damp and daylight together.
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Frequently asked questions
Do seeds need light to germinate?
Some do, most do not, and a few need the opposite. Of 78 common garden plants, 24 will not germinate reliably unless the seed sits on the surface where daylight reaches it, 7 need to be covered and will do badly if left exposed, and 47 have no strong preference and simply want sowing at an ordinary depth. Burying a light-requiring seed is one of the most common reasons a tray never comes up.
How deep should I plant seeds?
The usual rule is two to three times the seed's own width, and it holds for most things. The exceptions are what catch people out: seed that needs light must not be covered at all, only pressed onto the surface so it makes contact, and a handful of species need to be deeper than the rule suggests because they want darkness. When a packet says 'surface sow' or 'needs light', that instruction overrides the rule.
What happens if I bury a seed that needs light?
Usually nothing at all — it sits there and does not germinate, and the tray looks like a failure of the seed. Some of it may come up unevenly if a few seeds end up shallower than the rest, which is why a patchy tray is often a sowing-depth problem rather than a bad batch. If you have buried them and nothing has happened, sowing a second batch on the surface is quicker than waiting.
Do yarrow seeds need light to germinate?
Yes. Yarrow is one of the clearest cases on this list — surface sow it and never bury it. Burying yarrow is the usual reason a tray comes up empty, and it gets blamed on dormancy when yarrow needs no cold period at all.
Do calendula seeds need light or darkness?
Darkness. Calendula is the opposite of yarrow: it wants covering, about 6mm deep. Left uncovered on the surface it germinates poorly. It needs no cold treatment whatsoever, so if a calendula tray fails, depth is the first thing to check.
How do I keep surface-sown seed from drying out?
That is the real difficulty with light-germinating seed, because the surface is exactly where compost dries first. Press the seed onto firmed compost so it makes proper contact, water from below by standing the tray in shallow water, and cover the tray with a clear lid or a propagator top until germination. Watering from above washes fine seed out of position.