How to Grow Lupines from Seed: Scarifying, Sowing Depth and the Taproot Problem

Know first what seed will and will not give you

Seed saved from a garden lupine does not reproduce the plant it came from. Almost every border lupine is a hybrid, its color held together by breeding rather than by anything the seed carries, and the offspring segregate immediately. Sow a hundred seeds from a clear pink or a bicolour and the great majority come up in muddy blue, dull purple or a washed-out mauve, with a scattering of something better and a lot of plants that look tired next to their parent.

That is not a reason to avoid seed. It is a reason to be clear about what you are sowing for. Seed is the cheap, fast way to fill a bank or a wide drift with dozens of plants, and a drift of mixed blues and purples with the odd surprise in it is a good thing to have. It is also the only sensible way to replace lupines at the rate they need replacing, because these are short-lived perennials that fade after three or four years.

What seed cannot do is keep a particular plant going. If you have one lupine whose color you actually want, propagate it from basal cuttings taken off the crown in spring, and treat its seed as a separate, unrelated project. Sowing seed from that plant and expecting more of it is the single most common disappointment in growing lupines.

Species lupines are the exception. Grown apart from hybrids they come reasonably true from seed, which is why self-sown colonies on roadsides and railway banks stay consistent year after year while a garden bed drifts.

If you sow seed near an existing named plant, mark which is which before the foliage overlaps. Seedlings grow faster and heavier than a settled hybrid and will crowd it out within two seasons if you cannot tell them apart.

Break the seed coat, or wait a very long time

Lupine seed is a hard, smooth, pea-like thing built to survive years in the soil, and it is waterproof. Sown dry it may take six weeks to germinate, may germinate in scattered batches over two seasons, or may simply rot before it takes up any water at all. Every reliable method comes down to letting water through that coat.

Soaking is the easiest. Drop the seed in water at room temperature and leave it overnight, up to twenty-four hours. In the morning the seeds that have worked have visibly swollen, gone soft and lost their gloss. Sow those immediately, while they are plump. The ones still hard and shiny have not taken up water, so nick each of those with a knife or rub it on fine sandpaper until the coat is dull, then soak again for a few hours.

Nicking is more work but more certain. Take a sharp blade and cut a shallow sliver off the coat on the side away from the small pale scar where the seed was attached, deep enough to see the paler layer beneath but not into the seed itself. Sandpaper does the same job more crudely; a small jar lined with coarse sandpaper, seed shaken in it for thirty seconds, is enough for a large batch.

Once the coat is open, germination is quick and even. At soil temperatures of 60-70F (15-21C) expect the first shoots in seven to ten days and most of what is going to come up within a fortnight. Below 50F (10C) germination stalls and the swollen seed is very likely to rot instead.

Sow deep pots or sow where they are to grow

A lupine seedling puts down a taproot far faster than it puts up leaves. Within three weeks of germinating it has a root longer than the shoot, and that root does not forgive being broken, bent or coiled. Every sowing decision follows from this.

If you sow in containers, use deep ones. Root trainers, four-inch (10 cm) deep tubes, or tall pots sown with two or three seeds each and thinned to one all work. Shallow seed trays do not: the root hits the base in a fortnight, turns and circles, and the plant never fully recovers even after planting out. Move seedlings on or plant them out while they are small, at two or three true leaves, and take the whole rootball out without shaking soil off it.

Direct sowing avoids the problem entirely and gives noticeably stronger plants. Sow once the soil is workable and above 55F (13C), a quarter to half an inch (6-12 mm) deep, in stations of two or three seeds spaced a foot (30 cm) apart, and thin to the best seedling in each station. On a bank or in a wild drift this is by far the best method, because the plants root straight down into undisturbed ground.

The one thing to get right first is drainage. Lupines want a well-drained, sandy or gritty soil, ideally neutral to slightly acid. On thin chalk they turn yellow between the veins and sulk; on ground that lies wet in winter the taproot rots and the plant vanishes without warning. Neither condition can be fixed after sowing, so choose the site before you scarify anything.

From seedling to first spike, and what to write down

Spring-sown seedlings make a low rosette of the familiar fingered leaves through their first summer and usually flower the following season. Some vigorous ones throw a small spike in their first autumn; cut it off, because a first-year plant that sets seed spends its energy on that instead of on building the crown it needs for a proper display next year.

Late summer sowing also works where winters are not severe. Those seedlings overwinter as small rosettes and flower properly the following summer, often a little earlier and a little stronger than spring-sown plants of the same age. In hard-winter areas keep them in a cold frame rather than risk them in open ground at rosette size.

Slugs are the real hazard of the first few months. A lupine seedling can be eaten to the ground overnight, and unlike an established plant it does not come back. Protect the seedlings until the leaves are leathery and three or four inches (8-10 cm) across.

Keep a note of the sowing date, the germination date, and how many of the batch actually came up after scarifying. That last number tells you next year whether your soaking was long enough or whether the seed source was poor. When the seedlings flower, record the color of each one and its position, because that record is what lets you pull the muddy ones out and keep the two or three worth taking cuttings from. Without it, everything in the bed looks the same in spring when you need to decide.

Sow a small batch every year rather than a big one every four years. Lupines are short-lived, and a rolling supply of one and two year old plants means you never have a gap when an old crown finally gives out.