Sowing Viola Seed: Temperature, Darkness, Timing and Transplanting seedlings

When to sow, and why the timing is awkward

Sow ten to twelve weeks before your first expected frost for an autumn planting. That gives a plant with a solid crown and working roots by the time cold weather arrives, which is what allows it to flower through autumn and hold through winter. Sow later and you get a small plant that spends winter merely surviving. Where winters are severe, sow instead in late winter under cover, eight to ten weeks before you intend to plant out in early spring.

The awkwardness is that the late summer sowing date lands in the hottest weeks of the year, and viola seed will not germinate in heat. Germination is best between 60F and 68F (15C and 20C), falls away sharply above 75F (24C) and is close to nil at 80F (27C). This is the single reason most home sowings fail, and it is a sowing problem rather than a seed problem: the same packet sown into a cool place germinates fine.

So sow indoors or in the coolest shaded place you have, never directly into open ground in late summer. A north facing windowsill in an unheated room, the floor of a shed, a shaded cold frame with the lid propped, or the coolest corner of a garage with good light all work. Some people chill the sown tray in a refrigerator for two or three days before moving it into the cool place, which sharpens germination in a hot spell. Getting the temperature down is worth more effort than anything else in this whole process.

Sowing in trays, and why the seed goes in the dark

Fill a tray with fine seed-starting mix, level it, firm it lightly and water it before sowing rather than after, so you do not wash the seed around. Scatter the seed thinly across the surface, aiming for roughly half an inch (12 mm) between seeds, which saves a great deal of trouble at transplanting seedlings. Then cover with a shallow layer of sieved compost or vermiculite, about an eighth of an inch (3 mm), just enough to hide the seed from light.

That covering is not optional. Unlike many small seeds, violas germinate better in darkness, and seed left uncovered on the surface comes up thinly and unevenly. Some people go further and lay a sheet of black plastic or newspaper over the tray until the first seedlings show, which works well provided you look under it daily from day eight, because seedlings held in the dark after emergence stretch fast and never recover.

Keep the compost just damp. Water from below by standing the tray in an inch (2.5 cm) of water until the surface darkens, then take it out and let it drain, which avoids disturbing the covering. Expect seedlings in ten to fourteen days, often over an extended period rather than all at once, so do not clear a tray that looks half empty at two weeks. Uncover as soon as the first seedlings appear and move the tray to the brightest cool place you have.

1. Water the compost before sowing Fill and firm the tray, then water it and let it drain. Sowing onto pre moistened compost means you never have to water heavily over the seed and shift it out of place.
2. Sow thinly, about half an inch (12 mm) apart Crowded seedlings stretch, tangle their roots and are far harder to transplant cleanly. Tipping the seed into a folded paper crease gives you much better control than pouring from the packet.
3. Cover with an eighth of an inch (3 mm) Sieved compost or fine vermiculite. Viola seed needs darkness to germinate well, and this thin layer supplies it without burying the seed too deep to emerge.
4. Keep the tray at 60F to 68F (15C to 20C) The coolest shaded place you have with reasonable light. In a hot spell, a shaded cold frame or an unheated indoor room beats anything outdoors in the open.
5. Check daily from day eight Uncover the moment the first seedlings show. Every extra day in the dark after emergence produces stretched pale seedlings that never make compact plants.
6. Move to full light immediately Once germinated, seedlings want bright light and cool air, around 50F to 60F (10C to 15C). Warmth without light is what ruins most home raised violas.

Transplanting seedlings and growing on

Transplant at the first true leaves, which are the pair that follow the two rounded seed leaves and look like small viola leaves. That is usually two to three weeks after germination. Handle every seedling by a leaf and never by the stem: a crushed leaf costs you nothing and a crushed stem kills the plant. Lift each one with a dibber or a pencil point, working under the roots rather than pulling from above.

Move them into plugs or small pots of all-purpose potting mix, one per cell, setting each seedling so the seed leaves sit just above the surface. Firm gently, water in from below, and keep them out of direct sun for a couple of days while they settle. Then grow them cool and bright. Somewhere around 50F to 60F (10C to 15C) with as much light as you can give them produces short sturdy plants; a warm dim windowsill produces long pale ones that never firm up, whatever you do later.

Start a half strength liquid feed weekly from about two weeks after transplanting seedlings. Pinch each growing tip out once when the plant has four or five true leaves, which gives two shoots instead of one. Violas branch more freely after this pinch than pansies do, so the difference in the finished plant is substantial and the fortnight it costs is repaid several times over. Harden off over seven to ten days before planting, moving trays outside for longer each day, and plant out eight to ten weeks after sowing while the soil is still above 45F (7C).

Damping off, thinning and the problems that show early

Damping off is the failure that takes a whole tray. Seedlings topple at soil level, the stem shrunken and dark right at the surface, and it spreads outward from one point in a matter of days. It is caused by sowing too thickly, compost kept too wet, still air and reused unwashed trays. Prevent it rather than treat it: sow thinly, water from below and let the surface dry between waterings, give the tray moving air, and wash trays and pots in hot soapy water before use. Once it starts, remove the affected seedlings and the compost around them at once and let the rest dry a little.

Thin what does come up. Where two seedlings have come up touching, snip one off at compost level with scissors rather than pulling it, which would disturb the roots of its neighbor. Violas germinate over an extended period, so also resist the urge to transplant everything on one day; take the ones at the true leaf stage and leave the later ones another week.

Sowing your own saved seed is worth understanding before you spend a season on it. Violas cross freely with each other and with pansies nearby, so saved seed will not come back like the parent, and a plant you particularly liked has to be increased from cuttings or division instead. Saved seed is still worth sowing for the quantity and the toughness of what comes up; just do not expect the colors you collected from.

Write down the sowing date, the temperature where the tray sat, and the date the first seedlings appeared. Germination in this plant is almost entirely a temperature story, and two seasons of those three numbers will tell you exactly which spot in your house or garden to use next time.