How to Grow Nasturtiums: A Practical Guide from Seed to Flowers

Nasturtiums are one of the easiest flowers you can grow from seed and a great choice if you're fairly new to gardening. The seeds are large, germinate readily and the plants don't need much attention once they're established.

They're very versatile too. Compact varieties are ideal for pots, containers and the front of borders, while more vigorous types will happily trail over edges and grow through other plants.

One thing I've learnt with nasturtiums is that they will mainly look after themselves. Put them into very rich soil and feed them enthusiastically and you can end up with enormous leaves and surprisingly few flowers. Average soil and a sunny position usually give a much better display.

The flowers and young leaves are edible too, with that distinctive peppery flavour.

Sow them in spring, keep young plants away from frost and, once established, they'll usually flower from early summer until the colder weather eventually brings the display to an end.

When to Sow

Nasturtiums grow quickly, so there's very little advantage in starting them too early.

You can sow indoors from March or April if you'd like to get plants underway before the weather outside is suitable. I usually sow a few seeds in each pot because the seeds are large and easy to handle.

For direct sowing outside, wait until April or May when the soil has started to warm. In colder gardens, I usually sow in May rather than putting seeds into cold, wet ground and hoping they germinate.

You can continue sowing into early summer if you want later flowers.

Nasturtiums are tender, so don't rush young plants outside simply because you've had a couple of sunny April afternoons. Frost can quickly damage them.

If you've started plants under cover, harden them off before planting outside once the danger of frost has passed.

There's no need to sow dozens either. Nasturtiums grow rapidly once conditions improve and a handful of healthy plants can cover a surprising amount of ground.

How to Sow

Nasturtium seeds are wonderfully easy to handle.

For sowing in pots, fill small pots with multipurpose compost and sow two or three seeds in each, around 1–2cm deep. Cover with compost, water gently and put them somewhere reasonably warm.

Keep the compost moist but not soaking wet.

Seedlings usually appear fairly quickly in good conditions. Once they emerge, move them into plenty of light so they develop into sturdy plants rather than long, stretched ones.

For direct sowing, prepare the soil, make holes around 2cm deep and space the seeds roughly 20–30cm apart, depending on the variety. Cover them with soil and water if conditions are dry.

There are lots of different types and some are much less vigorous than others. Tom Thumb types need less room than vigorous trailing varieties.

Nasturtiums generally prefer being sown where they're going to grow or moved while still young. They don't particularly appreciate having a large root system disturbed.

And don't worry about creating perfect rows. Nasturtiums look particularly good allowed to wander naturally through gaps in a border.

Planting Out and Spacing

Plant nasturtiums outside once the danger of frost has passed and your young plants have been hardened off.

Choose a sunny position if you want plenty of flowers. They'll tolerate some light shade, but you may get more foliage and fewer blooms.

The interesting thing about nasturtiums is that better soil doesn't necessarily mean better plants. They grow perfectly happily in ordinary garden soil and often flower particularly well where conditions aren't overly rich.

Spacing depends on the variety. Compact types can generally be planted around 20–30cm apart, while vigorous trailing varieties need considerably more room.

Nasturtiums are excellent in containers, although choose the pot to suit the variety. Compact types work well in ordinary pots and window boxes, while trailing varieties need enough room to spill naturally over the sides.

Water plants thoroughly after planting and keep them watered while the roots establish.

After that, they look after themselves.

Growing On

Once the weather warms, nasturtiums grow quickly.

Keep weeds under control while the plants are small, but once the foliage begins spreading, you'll find the nasturtiums do a pretty good job of shading the soil themselves.

Compact varieties generally form neat mounds, while trailing types can produce long stems that wander wherever they fancy. You can guide these over the edge of containers, along low supports or through other plants.

If a trailing stem heads somewhere you really don't want it, simply redirect it or trim it back. Nasturtiums respond perfectly well to a little tidying.

Remove badly damaged or yellowing leaves as the season progresses.

Keep an eye on vigorous plants around neighbouring flowers too. Nasturtiums are charming when they're scrambling through a border, but occasionally need reminding that the entire border wasn't planted exclusively for their benefit.

Watering and Feeding

Established nasturtiums growing in the ground are fairly tolerant of dry conditions.

Water young plants while they're establishing and, after that, give them a drink when the ground gets really dry. There's generally no need to keep the soil permanently damp.

Plants growing in containers will need more attention because pots dry out much faster than open ground. Check them regularly during warm weather.

In ordinary garden soil, I generally wouldn't feed nasturtiums at all. Too much fertiliser, particularly nitrogen, encourages masses of lush foliage at the expense of flowers.

Container plants growing in the same compost for months may eventually need a little help, but don't automatically add liquid feed every week simply because they're flowering plants. If they're healthy and producing plenty of blooms, leave them alone.

If you have spectacularly large leaves but hardly any flowers, feeding is one of the first things I'd reconsider.

With nasturtiums, a little neglect often produces a better display than too much kindness.

Flowering and Picking

Nasturtiums usually begin flowering in early summer and can continue well into autumn if conditions remain mild.

Remove faded flowers if you want to keep plants looking tidy and encourage them to continue blooming. You don't need to inspect them daily, but going over the plants occasionally makes a difference.

If you'd like to save seed, leave some flowers towards the end of summer and allow the seed pods to develop and mature.

Both the flowers and young leaves are edible. They have a peppery flavour and the flowers look particularly good scattered through salads. Only eat flowers from plants you know haven't been treated with unsuitable pesticides or other chemicals.

Pick flowers when they're fresh and fully open.

The leaves can be harvested throughout the season, although don't strip huge amounts from a plant you're also expecting to produce masses of flowers.

And don't overlook the flowers simply because they're edible. Nasturtiums are worth growing purely for the display — being able to put some of it on your plate is just a bonus.

Common Problems

Blackfly and Aphids

Nasturtiums have an impressive ability to attract aphids, particularly blackfly.

You may sometimes see whole stems covered with them. Small infestations can be squashed or washed away with water, while ladybirds, hoverfly larvae and other beneficial insects will often arrive to help.

This attraction to aphids is also one reason nasturtiums are sometimes grown alongside vegetables.

Caterpillars

Cabbage white butterflies sometimes lay eggs on nasturtiums, and their caterpillars can make short work of the leaves. There have been years when they've eaten nearly all my plants before I've even noticed.

Check underneath the foliage if you're suddenly seeing lots of holes. A few chewed leaves won't seriously trouble a vigorous plant, but large numbers of caterpillars can strip one remarkably quickly.

Slugs and Snails

Young seedlings can be damaged by slugs and snails, particularly during damp spring weather. Keep an eye on plants until they're established.

Larger nasturtiums are generally vigorous enough to cope with the occasional nibble.

Lots of Leaves but No Flowers

This is one of the most common nasturtium problems and rich soil or too much feeding is often responsible.

Nasturtiums don't need luxurious conditions. If plants are producing enormous amounts of foliage, stop feeding them and give them as much sunshine as possible.

Yellowing Leaves

A few older yellow leaves are nothing to worry about. Widespread yellowing can be caused by waterlogged soil, exhausted container compost or simply plants reaching the end of their season.

Poor Flowering in Shade

Nasturtiums will grow in partial shade, but they generally flower much better with plenty of sunshine. If you've got huge healthy plants but disappointing flowering, have a look at how much light they're actually receiving.

Nasturtiums aren't plants I spend much time fussing over. Give them some sun, don't feed them too much and keep an occasional eye out for caterpillars. Most years they'll do the rest themselves — usually spreading considerably further than you remember planting them.