Sowing Snapdragon Seed: Surface Sowing, Light and Temperature

Surface sow and do not cover the seed

Snapdragon seed is about the size of ground pepper, and a single seed carries almost no food reserve. It germinates in light, and burying it under even a quarter inch (6 mm) of compost is the single most common reason a tray comes up empty. Fill the tray, firm it level, water it before sowing so the surface is already damp, then scatter the seed on top and press it down with a flat piece of board so it sits in contact with the compost without disappearing into it.

Because the seed is so fine, sowing evenly is a skill in itself. Tip a small quantity into the palm of one hand and tap it out with a finger, moving steadily across the tray, or mix it with a pinch of dry silver sand so you can see where it has landed. A tray sown too thickly is not a bonus. Crowded seedlings stretch toward the light, tangle at the root, and damp off in a block once the first one goes.

Do not water from above after sowing. A watering can washes the seed into corners and buries half of it. Stand the tray in an inch (2.5 cm) of water until the surface darkens, then take it out and let it drain. From then on, water from below whenever the surface starts to pale, and keep a sheet of glass or a clear lid over the tray to hold humidity until germination.

Germination takes ten to fourteen days at the right temperature, and it is not even. Seedlings appear over a week or more, so do not give up on a tray after the first flush. Remove the cover as soon as the first seedlings are through, because the same humidity that helped the seed germinate will kill the seedlings within days if it is left in place.

Warm to germinate, then cool to grow on

The temperature that suits the seed is not the temperature that suits the seedling. Germinate at 65 to 70F (18 to 21C) on a windowsill or a heated bench, then move the tray somewhere distinctly cooler as soon as the seedlings are up. Grown on at 50 to 60F (10 to 16C) in the brightest place you have, a snapdragon seedling stays short, thick stemmed and dark green, and it branches from the base without being asked.

Left in the warmth, the same seedling is pale, leggy and falls over in the tray. That stretch is never recovered. A plant that has been drawn up as a seedling makes a thin spike later, however well you feed it afterward, so the cool bright period between germination and planting out matters more than anything you do in the ground.

Sow eight to ten weeks before your last frost date if you want flowers in early summer. Snapdragons are cool season plants that flower best before high summer, so the aim is a sturdy plant ready to go out as soon as the ground can be worked, not a large plant held indoors until the weather is warm. Young plants tolerate a light frost once hardened, which is why they can go out earlier than most annuals.

In regions with mild winters, an autumn sowing is the better option altogether. Sown in late summer and planted out in autumn, the plants root through the cool months and flower in early spring on stems far longer than any spring sowing can manage, well before the heat that shuts flowering down.

1. Prepare and pre wet the tray Fill with a fine seed-starting mix, firm level, and water from below until the surface is evenly damp. Sowing onto dry compost means watering afterward, which buries the seed.
2. Scatter thinly and press down Tap the seed out across the surface, mixing with dry sand if you find it hard to see. Press it into contact with a flat board. Do not sieve compost over the top.
3. Cover the tray, not the seed Put glass or a clear lid over the tray to hold moisture and keep it at 65 to 70F (18 to 21C) in the light. Check daily and remove the cover at the first sign of seedlings.
4. Move to cool and bright immediately Once up, growing on at 50 to 60F (10 to 16C) with maximum light is what produces a stocky plant. Warmth and dim light at this stage ruin the plant permanently.
5. Transplant at the first true leaves Lift seedlings by a leaf, never the stem, and move them into cells or small pots at about an inch (2.5 cm) apart. Left longer, the roots knit together and separating them tears them.

Hardening off and going into the ground

Harden off over ten to fourteen days before planting. Start with a few hours outside in a sheltered spot, build up to a full day, then leave the plants out overnight once there is no hard frost forecast. Plants moved straight from a warm bench into open ground stall for two or three weeks, and that stall costs you the early flowering that made the early sowing worthwhile.

Plant into ground that has been dug over and has some compost worked in, but do not enrich it heavily. Snapdragons flower well on moderate soil and grow soft on rich soil, and soft growth is what rust and aphids find first. Firm the plants in properly, because a tall spike in loose ground rocks in the wind and the stem base loosens.

Space by the type you are growing. Tall kinds want 8 to 12 inches (20 to 30 cm) between plants so air moves through the row, and dwarf kinds are fine at 6 inches (15 cm). Crowding is the direct cause of rust later in the season, and no amount of spraying makes up for plants set too close together.

Water them in and keep them damp for the first fortnight while they root out. After that a snapdragon is fairly drought tolerant and does not need coddling. Get the support in for tall types now rather than later, because pushing canes in beside an established plant cuts through the root plate.

Do not throw away a tray that looks like a failure at two weeks. Germination is uneven and staggered, and trays regularly double their seedling count between day twelve and day twenty. Keep it damp, keep it in the light, and give it another fortnight before reusing the compost.

What to write down at sowing time

Record the sowing date and the date the first seedlings appear. The gap between the two tells you whether your germination temperature was right: much beyond fourteen days and the tray was too cold, a poor and patchy result and it was probably too warm. That one number, kept for two seasons, removes all the guesswork from the following year.

Note the date you transplanted and the date you planted out, alongside the date of the first open flower. Snapdragons take fourteen to eighteen weeks from sowing to flower, and your own figure for your own conditions is worth more than any general one. Once you know it, you can count backward from the week you want flowers.

Write down how many seedlings you actually got from a sowing, not how many you sowed. Snapdragon seed is fine enough that most people sow far more than they need and then find they have twenty plants and space for eight. A realistic figure prevents both waste and disappointment.

Keep a note of where each batch was grown on. If one windowsill produced stocky plants and another produced leggy ones, that is a light difference, and it is the single most useful thing you can learn about your own house before next spring.