Nasturtium Growing Calendar: Sowing to First Frost

The year at a glance

Nasturtium is a tender annual in most temperate gardens: sown after the last frost, flowering from midsummer, killed by the first autumn frost. The work is light and concentrated in three places. Getting the soil deliberately poor before sowing, deadheading and pod picking through summer, and collecting seed before the frost.

Spring: choose the ground and wait

The whole season is decided before you sow, by where you put it. Walk the garden in early spring and pick out the lean spots: unimproved ground, the base of a wall, a gravelly strip, a container of last year's compost. Mark those and leave them alone. Do not dig in manure, do not scatter a general fertilizer, do not top up a pot with fresh rich compost.

Then wait for the soil to warm. Nasturtium germinates from 55F (13C) and rots below 50F (10C), and the plant is frost tender from the moment it emerges, so there is nothing to gain from an early sowing. In a slow spring, start a few in individual three inch pots and plant them out small, before the taproot fills the pot.

1. Late winter Check your saved seed by soaking ten overnight and seeing how many swell. Decide how many trailing and how many compact plants you want, and where each will go.
2. Mid spring Clear the stations of weeds and firm the soil. Add nothing. If a bed has just been manured for something else, pick a different bed for the nasturtium.
3. After the last frost Sow two seeds per station an inch (2.5 cm) deep, at 9 to 12 inches (23 to 30 cm) for compact types and 18 to 24 inches (45 to 60 cm) for trailing ones. Water the hole, not the surface.
4. Two to three weeks later Seedlings appear in seven to twelve days in warm soil. Thin to one per station by cutting the weaker one off at ground level.

Sow the trap plants alongside the beans at the same time as the beans, so the nasturtium is established before the first aphids fly in.

Early summer: growth, and the aphids arrive

Growth is fast once the nights are warm, and trailing types start running. This is when blackfly appear, usually within a fortnight of the beans coming into flower. Decide now which plants are decoys, to be left alone, and which are for eating, to be kept clear by hand.

Flower buds start in the leaf joints from about midsummer. If by then you are looking at a mound of enormous leaves with no buds, the soil is too rich: stop watering, feed nothing, and give it four weeks of hard treatment before you conclude the plant is a failure.

Midsummer to high summer: the picking season

Everything happens at once now. Leaves and flowers are at their best, the first green pods appear a week or two after flowering starts, and the plant needs going over twice a week. One pass covers all of it: deadhead the faded flowers, pick the young leaves and open flowers for the kitchen, and take every pod that is still soft enough to dent.

By late in this period the oldest runners go bare and yellow at the base and flowering slows. Cut the whole plant back by half with shears, water it once, and leave it. It regrows and reflowers within about three weeks, giving a second season that runs to the frost.

1. Twice a week, one pass Deadhead, pick leaves from the outside of the plant, take the open flowers, and collect soft green pods. Doing it as one job is what keeps it manageable.
2. Hold pods in brine as you go A single picking is never enough for a jar. Keep the pods in salted water in the fridge and pickle a batch every fortnight.
3. Cut back when it tires When the base goes bare and the flowers thin out, shear the plant to half its size. Do this by late summer so there is time to regrow before the cold.
4. Leave one runner to pod up Set aside part of the plant, or one whole plant, and stop deadheading it. That is where your seed for next year comes from.

In a heatwave above 86F (30C), flowering pauses and buds drop. Do not respond by feeding. Shade at midday, water at the root, and it resumes when the nights cool.

Autumn: seed, then the frost ends it

Flowering picks up again as the nights cool and often the best display of the year comes in early autumn. Meanwhile the seed is ripening and falling, so get under the plants on a dry day and collect the pale corky seeds off the soil. Dry them a fortnight indoors before storing.

The first frost kills nasturtium outright. The plant blackens and collapses overnight, and there is no partial damage and no recovery, so anything you want, whether pods, flowers or seed, has to be taken before it. Pull the dead growth and compost it, unless the plants had virus or heavy aphid, in which case bin it.

Clearing the dead plants does not stop next spring's volunteers, because the seed is already in the soil. If you want a bed clean, hoe the seedlings off in late spring instead.

The three dates worth writing down

Nasturtium repeats itself closely from year to year in the same garden, so a very short record is enough to run it well. Note the date the first flower opened, the date you first saw aphids and on which plant, and the date of the frost that killed the plants. Those three fix the whole schedule for next season.

Add one line about each station: what the soil was like, and whether the plant flowered or made a leaf mound. That is the record that saves you a wasted season, because the leafy failures are always the same corners of the garden and you will not remember which ones by next spring.