How to grow Nemesia

What are nemesias?

Nemesias are members of the snapdragon family (Scrophulariaceae), along with many other popular garden plants, including Diascia and verbascum. They tend to be compact, branching plants with pretty flowers in one or two colours, often with yellow throats and sometimes fragrant. They need protection from frost and will bloom best in the cool temperatures of spring or autumn – flowering will often finish early in hot, dry weather. There are many different cultivars of nemesia, in a wide range of colours.

Choosing nemesias

Nemesias are small plants, 20-35cm tall. Some have a trailing habit, which lends itself well to hanging baskets in particular. The most commonly grown species are the annual Nemesia strumosa and the perennial

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

N. caerulea, but nemesias are widely hybridised and are often grouped in collections, or ‘series’, of similar cultivars.

With the exception of the ‘Melody’ collection (which are hardy to H5), nemesias grown as garden plants in the UK are often treated as annuals

Annuals are plants that complete their life cycle in one growing season. They are generally easy to grow from seed or can be bought as young plants from garden centres. Annuals are ideal for growing in summer containers and filling gaps in borders. Some examples of annuals include sunflowers, cosmos, sweet peas and zinnia.

. Many are tender perennials that will only survive winters in relatively mild areas. Their size and lifespan mean that they are best displayed in containers, or as bedding plants

Bedding plants are usually colourful half-hardy, short-lived or annual plants, grown for displays in beds or containers. They may be changed seasonally, with spring, summer and winter bedding displays each using different plants of appropriate hardiness and flowering times.

at the front of the border. 

After habit (bush or trailing) and scent, the main consideration when choosing nemesias is which of the great variety of colours you prefer. For a soft, relaxing mood, consider the pretty pastels of cultivars like Nemesia ‘Lilac Queen’ or N. ‘Ayana’, or the lightly fragrant blues and whites of N. ‘Nuvo Blue’ or N. ‘Wisley Vanilla’. If exotic is more your vibe, what about the fruit-salad colours of the large-flowered N. NESIA TROPICAL or the semi-trailing crimsons and gingers of the Sunsatia Series? Or perhaps your tastes are more sophisticated, in which case take a look at the classy bicolour cultivars like the mouth-watering N. RASPBERRIES AND CREAM or N. NESIA BANANABERRY.

To help you choose the perfect nemesia for you, look for those that have received the RHS Recommended: Award of Garden Merit, as these have been assessed and are known to perform well. Use the RHS Find a Plant tool to browse images and focus your search on criteria for your particular requirements.

Buying nemesias

Nemesias are widely available from garden centres and nurseries as 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.

or potted plants in spring and summer, or you can obtain some species and cultivars as seed, which is easy to grow. Use our Find a Plant tool for stockists.

When

Nemesias are mostly tender plants, so need to be protected from frost. It’s therefore best to wait until early summer before planting them outside. You can of course pot up containers sooner than this, but protect them from frost with biodegradable

Anything that can be decomposed by fungi, bacteria and micro-organisms, so it doesn’t persist indefinitely in the environment. Biodegradable plastics are usually made from plants, such as bamboo, rather than fossil fuels. Ideally, products that claim to be biodegradable should break down quickly and leave nothing harmful behind. However, they may need specific conditions in order to biodegrade successfully or may produce greenhouse gases such as methane in the process.

fleece

A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops.

or keep them in an unheated greenhouse until the weather warms up.

Where

Choose a sunny, free-draining position in moist, mildly acidic, fertile soil. If your ground conditions aren’t favourable, then plant in a container instead (see below).

If your plants are bought as plugs, it’s best to pot them into containers first and allow them to grow to fill at least a 9cm pot before planting outside in the ground.

How

Dig a hole slightly bigger than the plant’s rootball

The roots and accompanying soil when a plant is removed from a container or lifted from the ground.

. Place the plant in the hole, backfill with soil and firm it in. Water well. 

How to grow annuals and biennials

How to plant up a container

Watering and feeding

It shouldn’t be necessary to feed or water nemesias in the ground, as long as conditions are suitable, unless there is a very dry spell. 

Watering

Weeding

Nemesias don’t tend to self-seed, so there is no need to weed out seedlings

A seedling is a young plant grown from seed.

. However, like any plants in the border, they may be encroached upon by more vigorous plants, so weed these out as necessary.

Mulching

Mulching isn’t necessary, but if plants are growing in a border then they can be mulched alongside their neighbours. Use well-rotted organic matter, like garden 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.

or leafmould, to help suppress weeds and lock in moisture.

Mulches and mulching

In containers

Use three parts good-quality ericaceous

Plants that thrive in acid or ericaceous soil, which has a pH of less than 7 (neutral). You can measure your soil pH using a simple testing kit. Ericaceous or acid-loving plants include rhododendrons, camellias, heathers and blueberries.

peat-free compost mixed with one part horticultural grit to grow nemesias in containers. Check the compost regularly with a finger to make sure it remains just moist, but not wet or soggy. 

Compost usually contains enough 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.

to last 3–6 weeks after planting. Either add some slow-release ericaceous fertiliser at the beginning of the season (according to the manufacturer’s instructions), or use a liquid ericaceous feed, to keep your nemesias performing well. Feed only during the growing season

The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

(March to October).

Growing plants in containers

Overwintering

Annual nemesias can be discarded at the end of the season. Many people also discard tender perennial

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

nemesias, but if you would like to try to overwinter them, cut them back by half and put them in a frost-free place such as an unheated greenhouse. Water sparingly, but don’t allow them to dry out. In spring, repot them into fresh, peat-free compost and water well; they can go outdoors in early summer, when all risk of frost has gone.

Caring for older plants

Perennial nemesias tend to be discarded before they get old, but if you manage to overwinter yours for a year or two, an annual prune should help keep them compact and bushy. Feed and water regularly, as described above, to keep them flowering well.

It’s worth pinching out the growing tips on seedlings

A seedling is a young plant grown from seed.

and 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.

to produce bushier, more floriferous plants. Once initial flowering has finished, shear off flowering shoots, cutting the plant back by about half, to encourage a second flush of flowers. 

By seed

Most annual and perennial

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs.

nemesias are easy to propagate from seed in early spring, at around 15°C for best germination

Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light.

rates. As nemesias can stop flowering in very warm weather, it may be worth making a second sowing to get an autumn display once the spring-flowering plants have faded.

How to sow seeds indoors

By cuttings or division

It’s also easy to propagate perennial nemesias by taking softwood cuttings

Softwood cuttings are taken from spring to early summer (Apr-Jun), using material from the soft and flexible young shoot tips from this seasons growth, which root readily. Use for hardy and tender perennials, deciduous shrubs, climbers and some trees.

in spring and early summer. 

Cuttings: softwood

Please be aware that some nemesias are protected by Plant Breeder’s Rights, and you are not allowed to propagate them for sale.

Nemesias are largely free of pests and diseases, though they may suffer from aphids, and root rot in wet conditions and high humidity

The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting.

.

If you are a member of the RHS, you can use our online Gardening Advice Service, via MyRHS, for any gardening problems or queries.