How to Sow Nasturtium Seed: Depth, Spacing and Why Not to Transplant

Sow direct, an inch deep, into the ground it will live in

Nasturtium seed is the size of a dried pea and pushes up through soil with real force, so it does not need the fussy shallow sowing that fine seed does. Sow it one inch (2.5 cm) deep. Sown shallower than half an inch the seedling often comes up wearing its seed coat, and mice and birds take it off the surface.

Sow it where it is to grow. Nasturtium makes a long, brittle taproot early and resents being moved: a plant lifted from a seed tray sulks for two or three weeks, and a check that early usually shows up later as a plant that flowers late. Direct sown seed beats a transplant even when the transplant went in first.

1. Make a proper hole, not a scrape Push a finger in to the first knuckle, drop one seed in, and close the soil over it. A seed pressed into the surface and covered loosely dries out on the top side and germinates unevenly.
2. Two seeds per station, thin to one Germination runs around eighty per cent, so sow two seeds at each station and pull the weaker seedling once both have their first round leaves. Cut it off at ground level rather than pulling, so the root of the keeper is not disturbed.
3. Water the drill, then sow Water the bottom of the hole before the seed goes in and do not water heavily again until the shoot appears. Repeated watering onto bare soil caps the surface and the shoot has to fight through a crust.

The seed keeps well. A packet three or four years old still germinates acceptably if it has been dry and cool, so there is no need to buy fresh every year.

Wait for soil above 55F, and do not sow before the last frost

Nasturtium germinates from about 55F (13C) and is quickest between 65 and 68F (18 to 20C), taking seven to twelve days. In cold, wet soil the fat seed simply rots. The plant itself is killed outright by the first frost, so nothing is gained by sowing early: wait until the last frost has passed and the soil has warmed.

In a cold, late spring you can start a few in three inch (7.5 cm) pots two or three weeks ahead, but plant them out while they still have only two or three leaves, before the taproot reaches the bottom of the pot. Sow one seed per pot and never prick them out of a shared tray.

Nick or soak the seed only if it is old

Fresh seed has a hard but permeable coat and comes up without help. Seed several years old, or seed you saved yourself and dried very hard, benefits from soaking in room temperature water overnight, which visibly swells it. Do not soak longer than twenty-four hours, because a seed left in water starts to ferment and will not grow.

1. Soak overnight, then sow the same day Put the seed in a cup of water in the evening and sow it in the morning. Swollen seed cannot be dried and stored again, so soak only as many as you intend to sow that day.
2. Nick the coat with a file For seed that stays hard and shrunken after soaking, rub one edge on a nail file until the pale layer under the coat shows. Do not cut into the middle of the seed where the shoot sits.
3. Discard the floaters Seed that is still floating after an hour in water is usually hollow. Throw those away rather than filling a station with them.

Do not enrich the soil before you sow

This is the one rule that decides whether you get flowers. Nasturtium evolved on thin, stony ground and, given rich soil or nitrogen fertilizer, it puts everything into leaf. You end up with a two foot mound of enormous round leaves, dark green and handsome, and almost no flowers. On poor soil the same plant covers itself in bloom.

So sow it into the parts of the garden you have not improved: the strip of gravelly ground by a path, the far end of a bed that has had nothing dug into it, or the second year of a container after a hungrier crop has stripped it. Never dig manure or a general fertilizer into a nasturtium station.

If you have already sown into rich ground, stop watering and feeding altogether and let the plant run dry between waterings. It usually starts flowering within a month of being made uncomfortable.

Spacing depends on whether it climbs or mounds

Trailing forms send out runners six to eight feet (2 to 2.5 m) long and will cover anything next to them, while compact forms stay as a mound about a foot (30 cm) across. Read the packet for which you have, because the spacing differs by a factor of three and a trailing type sown at nine inches will smother itself and mildew in the middle.

Write down the sowing date and the exact spot for each station. Nasturtium self-seeds heavily, and next spring you will want to know which seedlings came from your sowing and which came up on their own.