Germination temperature
About 18-21 °C (65-70 °F).
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Nasturtium has big, easy seeds that like to be covered, sown where they will flower and grown in lean soil. This guide covers soaking, sowing depth, why rich soil means fewer flowers, and the best season in India.
About 18-21 °C (65-70 °F).
About 1.3-2 cm (1/2-3/4 in); the seed needs darkness.
Usually 7-14 days, depending on soil temperature.
Darkness for germination: cover the seed fully. Full sun once growing.
Optional soaking for a few hours or overnight.
Direct sowing is best; nasturtium does not like root disturbance.
Nasturtium seeds are large, wrinkled and easy to handle, so you can place each one exactly where the plant should grow.
Not needed. Soaking softens the corky coat well enough; there is no need to file or nick the seed.
Not needed. Nasturtium is a frost-tender warm-weather annual with no cold requirement.
Optional but useful. Extension services recommend soaking seed in water for a few hours or overnight before sowing to improve and speed germination. Sow soaked seed the same day and do not leave it in water for days.
About 18-21 °C (65-70 °F). Seed sprouts faster in warm soil and slowly in cold, wet soil, so outdoors wait until the soil has warmed and frost is over.
Cover the seed with about 1.3 cm (1/2 in) of soil; drills about 2 cm (3/4 in) deep also work. Space seeds 25-30 cm (10-12 in) apart, or sow a little closer and thin later.
Ordinary, well-drained garden soil. Do not add compost or fertilizer to the sowing spot unless the soil is extremely poor.
Keep the seedbed evenly moist, not soggy, until seedlings appear.
Nasturtium needs darkness to germinate, which is why the seed is covered rather than sown on the surface. Seed left exposed on top of the soil germinates poorly.
Seedlings usually emerge in 7-10 days in warm soil and may take up to about 14 days in cooler conditions.
Nasturtium does not transplant well. For an early start, sow indoors 4-6 weeks before planting out in biodegradable peat or paper pots and plant the whole pot, so the roots are never disturbed.
Seedlings grow quickly in warmth and full sun. Water regularly while they establish; after that plants tolerate dry soil, though steady watering keeps them flowering.
Alaska is a compact, bushy nasturtium with cream-marbled leaves and a mix of flower colours, good for edges, pots and window boxes rather than for climbing.
Cause: soil that is too rich or heavily fertilized. Fix: grow in poor to average soil and stop feeding; nitrogen pushes leaf growth at the expense of flowers.
Cause: seed sown on the surface, soil too cold, or a waterlogged bed. Fix: cover seed with about 1.3 cm (1/2 in) of soil, sow after the soil warms and keep it moist rather than wet.
Cause: aphids, which are the most common nasturtium pest. Fix: rub or hose them off early, check leaf undersides and encourage ladybirds; avoid soft, overfed growth.
Cause: cabbageworm caterpillars chew leaves; leafminers leave pale tunnels that look bad but do little harm. Fix: hand-pick caterpillars and remove badly mined leaves.
Cause: strong heat and drought stress. Fix: give afternoon shade in hot climates, water regularly and grow nasturtium in the cooler season.
In the Indian plains nasturtium is grown as a cool-season annual: sow once the monsoon and summer heat are over so plants flower through the mild months. In hill areas it can be sown after the last frost and flowers through summer.
Full sun gives the most flowers; partial shade is tolerated but blooms less. In very hot summers afternoon shade helps.
Picking or deadheading the flowers prolongs blooming.
Leaves and flowers have a peppery, cress-like taste; young leaves are milder than old ones. Green seed pods can be pickled like capers. Only eat plants grown without pesticides, and keep in mind the roots are not edible.
Sow Nasturtium Alaska mix for compact plants with marbled leaves and bright, edible flowers.
It is optional but helps. Soak the seeds in water for a few hours or overnight and sow them the same day; this speeds up and evens out germination.
About 1.3-2 cm (1/2-3/4 in) deep. Nasturtium needs darkness to germinate, so the seed must be covered, not left on the surface.
Usually the soil is too rich or the plants were fertilized. Nasturtium flowers best in poor to average, well-drained soil in full sun.
It is better to sow directly where it will grow. If you start indoors, use individual biodegradable pots and plant them whole, because nasturtium dislikes root disturbance.