Sowing Salvia Seed: Timing, Temperature and Growing On

What is worth raising from seed

The bedding kinds with their dense scarlet and purple spikes are grown from seed as a matter of course, because they are treated as annuals and replaced every year. Several of the hardy border kinds also come readily from seed and give you a large number of plants for very little money, which is exactly what you want when filling a new border.

The tender shrubby kinds are a different case. They are almost always crosses, so their seedlings vary and will not reproduce the parent, and in any case they root from cuttings so easily that seed is the slower and less certain route. If you want more of a specific shrubby plant, take cuttings; if you want a quantity of plants and do not mind variation, sow seed.

Self-sown seedlings around an established plant are worth lifting rather than hoeing off. They vary, but a good proportion of them are perfectly usable garden plants, and they cost nothing.

Timing and temperature

Sow under cover in late winter, roughly eight to ten weeks before your last expected frost. That gives a plant of a decent size ready to go out as soon as the risk of frost has passed, and flowering by early summer. Sowing much earlier gives you leggy plants stuck in small pots waiting for the weather; sowing much later gives you plants that flower so late that half the season is gone.

Germination needs warmth: 70F to 75F (21C to 24C) is the target, and below about 65F (18C) germination becomes slow and erratic. A heated propagator or a warm spot indoors makes the difference between seedlings in ten days and seedlings in a month. Once the seedlings are up, drop the temperature to around 60F (16C), because keeping them at germination heat produces drawn, soft growth immediately.

Sowing direct outdoors is possible in warm climates once the soil is reliably above 65F (18C), but the plants flower much later and the seedlings compete badly with weeds at their smallest stage. Under cover is the more reliable route almost everywhere.

Sowing on the surface, because the seed needs light

This is the detail that catches people out. Salvia seed germinates in light, so it is sown on the surface of the compost and pressed into contact rather than buried. Covering it with a quarter inch (6 mm) of compost, which is the reflex for most seed, cuts germination sharply and is the usual explanation when a packet appears to have failed.

Use a fine seed-starting mix, level and firm it lightly, and water it thoroughly before sowing rather than after, so that the seed is not washed into clumps or driven under the surface. Scatter the seed thinly, press it down with a flat piece of card or the base of a pot, and cover the tray with a sheet of glass or a clear lid to hold humidity without excluding light. Keep it out of direct midday sun, which will cook a covered tray in minutes.

Once the first seedlings show, take the cover off. Salvia seedlings damp off readily in still humid air, and the transition from a covered tray to open air is the point at which most losses happen. Water from below by standing the tray in shallow water until the surface darkens, then take it out.

1. Fill and water the tray first Use a fine seed-starting mix, level it and firm gently. Water thoroughly and let it drain before you sow, so the seed sits on a damp surface and is not displaced by watering afterwards.
2. Scatter thinly and press, do not cover Sow thinly enough that the seedlings will not be touching. Press the seed into contact with the compost with a flat piece of card. Light is required for germination, so add no covering of compost.
3. Cover with glass or a clear lid and keep at 70F to 75F (21C to 24C) Hold the humidity but not the darkness. Seedlings appear in ten to twenty-one days. Remove the cover as soon as the first ones show, and drop the temperature to around 60F (16C).
4. Transplant at two true leaves Move each seedling to its own small pot once it has two true leaves beyond the seed leaves. Hold it by a leaf, never by the stem, and lever the roots up with a dibber rather than pulling.
5. Pinch the tip at four to six leaf pairs Take out the growing tip to force side shoots from the joints below. One pinch turns a single leggy stem into a bushy plant with several flowering shoots and costs about a week of flowering time.
6. Harden off over a fortnight, then plant out Move the plants outdoors for progressively longer each day over two weeks, starting in a sheltered spot. Plant out only after the last frost has passed, into full sun and free-draining ground.

Spacing and the ground you plant into

Space the plants according to how big the kind you are growing gets. Compact bedding kinds go at nine to twelve inches (23 to 30 cm) apart, and the larger border kinds at eighteen inches to two feet (45 to 60 cm). Crowding is the most common mistake, and it does two things: it produces stretched stems that fall over, and it holds still humid air in the middle of the planting, which is what powdery mildew needs.

Plant into full sun and free-draining ground. Do not enrich the planting hole heavily; salvias flower better in moderate soil, and rich ground gives leaf at the expense of spikes. On heavy soil, work grit through the whole bed rather than improving individual holes, and set the plants slightly proud of the surrounding level so water drains away from the crown.

Water every three or four days for the first six to eight weeks in dry weather, then stop. Established salvias want far less water than most gardeners give them, and the transition from attentive watering to leaving them alone is one many people never make.

Note the sowing date, the date the first seedlings appeared, and the date you planted out. Germination timing varies a great deal with the warmth you can actually provide, and one season's record is worth more than any figure on a packet.

What usually goes wrong

Nothing germinates: the seed was covered. Salvia needs light to germinate, and burying it is the single commonest cause of a failed tray. It is also worth checking the temperature, because below 65F (18C) germination is slow enough that people give up and throw the tray away while it is still viable.

Seedlings appear then collapse at soil level: damping off, caused by a humid still atmosphere and compost kept too wet. Remove the cover as soon as seedlings show, water from below, give the tray some air movement, and sow more thinly next time.

Seedlings grow tall, pale and floppy: too warm and not enough light after germination. Move them to the brightest place you have and drop the temperature. A drawn seedling never entirely recovers its stockiness, but pinching the tip at four to six leaf pairs salvages a usable plant.

Plants go out and then sit and sulk: planted too early into cold soil. Salvias will not grow until the ground warms, and a plant set out two weeks early is usually overtaken by one planted two weeks later into warm soil. Wait for the frost risk to pass properly.