How to grow annual nasturtiums

What are annual nasturtiums?

Annual nasturtiums are fast-growing plants that originate from Central and South America. The common name 'nasturtium' refers to species and cultivars of the genus Tropaeolum and reflects their similarity to the genus Nasturtium, which includes Nasturtium officinale (watercress).

They have fairly large, rounded leaves held firmly on long central stalks like an umbrella. Trailing types can use these long leaf stalks to climb by twining around supports. The flowers are typically wide-mouthed and trumpet-shaped, with five petals and often a long spur containing nectar

Sweet liquid mainly produced by flowers to attract pollinators. Honeybees make honey from nectar.

.

Choosing

There are two main types – dwarf/bushy cultivars such as the Whirlybird Series, reaching around 30cm in height, and climbing/trailing types such as ‘Darjeeling Double’, capable of growing to 2.5m.

Trailing varieties make bold ground cover and can spill over the side of a tub or hanging basket, or cascade down a wall or terrace. If provided with support, they will climb to make a colourful backdrop. Bushy varieties are excellent for bright colour in patio containers and borders.

The flowers come in a range of colours from creamy, pale yellow through dazzling orange to deepest red, with some having a combination of two or three colours and some being fully double. Most have round, green leaves with a slight blue-silver sheen, and some, such as the Alaska Series, are variegated

Variegated means having leaves or other plant parts with streaks, blotches or patches of different colours. Typically, these would be a combination of two colours, such as green and gold or green and white.

with bold flecks and sections of cream.

As they are cheap and short-lived, you can grow lots of different types or change what you grow every year. There’s no big commitment or great expense involved, so you can experiment and have fun. Self-seeded plants will be varied – not necessarily like the parent plant, but possibly even better!

When choosing, look in particular for varieties with the RHS Recommended: Award of Garden Merit. These performed well in trials, so should grow and flower reliably for you. To browse photos and descriptions of many cultivars, or to track down suppliers of specific varieties, go to RHS Find a Plant.

Buying

Nasturtiums are available all year round as packeted seeds, and in spring as young plug plants

Seedlings or young plants grown singly in small modules, with the advantage that they can be transplanted with minimal root disturbance. Bedding plants and young veg plants are often sold as plug plants of various sizes, with smaller ones requiring more aftercare. They usually need to be potted up and grown on indoors until large enough to plant outside.

, although the choice will be more limited. You can buy them in garden centres or online. Browse seed catalogues in the winter months for maximum choice.

Buying: garden centre plants

Buying: mail order plants

When to sow and plant?

Annual nasturtiums can be sown indoors in spring, to be planted outside after the last frost. 

If you buy plug plants

Seedlings or young plants grown singly in small modules, with the advantage that they can be transplanted with minimal root disturbance. Bedding plants and young veg plants are often sold as plug plants of various sizes, with smaller ones requiring more aftercare. They usually need to be potted up and grown on indoors until large enough to plant outside.

it’s advisable to plant them individually into 7–9cm pots, keeping them in a well-lit, frost-free place, with the compost

Can refer to either home-made garden compost or seed/potting compost: Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

just moist. Harden them off and plant them outdoors when the risk of frost has passed.

Alternatively, because they flower so quickly from seed, they are also successful when sown outdoors directly into the soil in late spring or early summer.

How to sow seeds indoors

When to plant out tender plants – avoiding late frosts

How to grow hardy annuals from seed in autumn

Where to plant

Nasturtiums like a sunny spot. They perform well on poor soil and can get too lush and leafy in very fertile conditions.

Bush varieties can be planted in summer containers, including large patio pots and window boxes, or in your borders. Trailing types can be planted in hanging baskets, to drape over the edge of a wall, as ground cover or trained up a trellis or over shrubs.

The leaves, seeds and young flower buds of many annual nasturtiums, including Tropaeolum majus, are edible, while the flowers bring a welcome blast of colour to the veg plot. There is a belief, supported by anecdotal evidence from some gardeners, that nasturtiums attract caterpillars and blackfly away from nearby crops, although scientific evidence for this effect remains limited.

Watering

Check and water seedlings

A seedling is a young plant grown from seed.

and young plants regularly for the first few weeks. After that, plants growing outdoors should only need watering during very dry or hot spells. However, these fast-growing plants don’t have time to develop extensive root systems, so do keep a close eye on them. 

Plants in containers, such as hanging baskets, patio pots and window boxes, need regular watering all summer, as they can dry out very quickly. 

Watering

Container maintenance

Feeding

Nasturtiums don’t need additional feeding when growing in borders. For those in containers, it’s best to add slow-release fertiliser to the compost

Can refer to either home-made garden compost or seed/potting compost: Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

when planting, to maximise flowering. See our guide to growing plants in containers.

Growing plants in containers

Weeding

Weeds can compete with your seedlings for light, water and nutrients

To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key nutrients usually taken up from the soil are nitrogen, phosphorus and potassium. Plants also need carbon, oxygen and hydrogen to make carbohydrates — their main energy source. Carbon and oxygen come from the air as carbon dioxide, while hydrogen is drawn from water absorbed by the roots. Other important soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough of these nutrients to support healthy plant growth.

, so remove them regularly. Once they are growing well, the umbrella-like nasturtium leaves can shade out weeds and provide good ground cover. 

Non-chemical weed control

No pruning is needed, though pinching out the growing tip will encourage extra branching. Regular deadheading

Deadheading is the process of removing spent flowers from plants to encourage more blooms and prevent seed production. This helps to redirect the plant's energy into producing more flowers rather than producing seeds.

will promote more flowers.

If you’d like them to climb, it is best to provide a support with narrow uprights, such as wire mesh, metal obelisks or string, that the leaf stalks can twine

Twine is a soft, fine loosely woven string treated with preservatives for outdoor use. Used for tying in climbers and other plants to supports.

around. Broader support structures, such as trellises, can be used but some tying-in may be needed.

Nasturtiums can be propagated from saved seed, although if your plants are hybrids or cultivars, the resulting seedlings

A seedling is a young plant grown from seed.

may not be the same as the parent plant. To know exactly what you are going to get, buy named, fresh seed each year.

Seed: collecting and storing

Nasturtiums are attractive to large and small cabbage white butterflies which lay eggs on the undersides of leaves. These hatch into caterpillars that eat the leaves and may do sufficient damage to reduce flowering. The best method of control is to inspect plants regularly and pick off eggs or young caterpillars, perhaps moving them on to plants you don't mind being eaten.

Nasturtiums also host aphids, especially the black bean aphid or blackfly. They can be kept in check by encouraging their many predators, including ladybirds, hoverflies, ground beetles, parasitoid wasps and earwigs. You can also pinch out

Removal of a plant’s growing tip (usually with finger and thumb) to encourage it to produce side-shoots, forming a bushier, well-shaped plant that will bear more flowers and/or fruits.

heavily infested shoot tips or flower buds.

If you’re a member of the RHS, you can use our online Gardening Advice Service, via MyRHS for all your gardening questions.