How to Grow and Care for Nemesia

The Nemesia genus contains more than 50 species, most of which are native to South Africa, but only a few are popular garden plants named cultivars. The two most popular species are N. strumosa and N. caerulea.

N. strumosa is a true annual that produces one-inch blue or white flowers and grows up to one foot tall. N. caerulea is a tender perennial that produces one-half-inch blossoms in purple, pink, blue, and white on plants that grow up to two feet. Even more common as garden plants are the hybrid forms derived by crossing various Nemesia species.

Nemesia plants feature lance-shaped leaves that appear in pairs along the stems, and the flowers bear a similarity to snapdragons, with a two-lipped, tubular shape. As long as temperatures remain mild, the plant can produce so many flowers that they almost entirely obscure the foliage from spring into fall. Usually planted as a garden-ready nursery plant in spring, it's also easy to grow from seed. Gardeners in cold-winter climates can seed directly into the garden for summer blooms or start them indoors for earlier flowering. Gardeners in warm-winter climates often seed directly into the garden in fall for winter bloom.

Nemesia Care

When buying nursery starts, look for seedlings that have lots of buds but only a few open flowers. Nemesia doesn't transplant well, so choosing plants that are not yet flowering will reduce stress. If growing from seed, start them seven or eight weeks before the last expected frost date.

Seedlings or potted nursery starts should be planted into the garden when all danger of frost has passed, spaced four to six inches apart. Choose a partially shaded area of the garden with rich, moist soil and adequate drainage. A layer of organic mulch will help insulate the roots from any temperature extremes as well as help the soil retain moisture. Once your nemesia plants are established in the garden, the plants actually won’t need much care aside from watering to help keep the soil moist.

Light

Nemesia will grow best in full sunlight, however, these plants may bloom longer (particularly in warmer climates) if they get some afternoon shade.

Soil

Nemesias require soil that's moist but well-drained, as well as rich in organic matter. Soil can be amended with sand, vermiculite, or perlite to improve its drainage.

Potted plants do well in an ordinary commercial potting mix amended with sand, vermiculite, or perlite.

Water

While it's important to keep the soil moist for these flowers, be wary of over-watering. Too much water will lead to stem rot.

Temperature and Humidity

Nemesia will grow best in cooler temperatures. In areas that have more mild summer temperatures, they can be expected to bloom from late spring until the first frost of the year, while in hotter climates they will look their best in early spring or fall, dying back somewhat during the heat of summer. These plants work well as winter annuals in frost-free regions.

Nemesia doesn't mind high humidity, though it may be more susceptible to powdery mildew and root rot in extremely humid climates. It works well in cool, dry climates if its soil moisture needs are met.

Fertilizer

Feed these plants once in the spring with a balanced time-release fertilizer. Or, you can choose a water-soluble fertilizer that can be applied twice monthly as they are actively growing.

Types of Nemesia

When selecting nemesia plants, you'll have a choice between pure species plants and hybrid cultivars:

• Nemesia caerulea 'Sea Mist' is a dense mat-forming cultivar that grows to about 18 inches tall. Its pale purple flowers bloom from late spring into fall.
• Nemesia strumosa ‘Carnival’ features compact dwarf plants with an upright growth habit. The flowers are yellow, purple, orange, pink, and white. N. strumosa is one of the parent species for many of the named hybrid cultivars. Look for N. strumosa 'Blue Gem' for true blue blooms or N. strumosa 'Triumph' for a bi-color bloom.
• Nemesia versicolor is available in a wide range of colors, including yellow, blue, white, and lilac. The popular 'Compacta' cultivar has white and blue flowers. N. versicolor is one of the parent species for many of the hybrid cultivars.
• Nemesia cheiranthus ‘Shooting Stars’ has unusual, exotic yellow flowers with long white spurs.
  
• Nemesia floribunda grows 12 to 24 inches in height and produces fragrant white flowers with yellow throats.
  

Among the popular hybrids, usually sold simply as nemesia:

• 'Berries and Cream’ has flowers that mix purple, mauve, and white colors. The growth habit is trailing. It is a compact plant with a full growth habit, flowering through summer and into fall.
• ‘Ice Pink’ has soft pink blooms. It is a compact plant with an upright growth habit, reaching about eight inches tall and 10 inches wide.
• ‘Rhubarb and Custard’ has unusual bi-colored purple and yellow flowers. It is a larger plant, growing to about 20 inches tall and 10 inches wide, and it is known to have better tolerance for heat than most cultivars.
• 'Sunshine’ has bright yellow flowers, blooming from spring into fall. The growth habit is upright; plants grow to about 12 inches tall and wide.
• ‘Tropical’ has flowers that blend orange and dark pink. Plants are 10 to 14 inches tall, with an upright growth habit.
• ‘Wisley Vanilla’ has flowers that are pure white with yellow eyes. These are upright plants growing to about 18 inches tall and wide. They have an especially strong scent.
• 'Aromatica True Blue' has soft blue fragrant flowers on 14-inch stems.
• 'Opal Innocence' offers lavender-gray flowers growing on a plant 8-inches wide with 16-inch stems. It flowers best in cooler spring or fall temperatures.
• 'Sunsatia Cranberry' is a trailing nemesia perfect for hanging baskets with bright red flowers and stems that trail up to 36 inches.
• 'Bluebird' has small, blue blooms and can withstand the heat of summer.
• 'Juicy Fruits® Kumquat' withstands the heat of summer without deadheading and has large blooms of gold, orange, and cherry red.

Pruning

Deadhead spent flowers immediately after they bloom to stimulate new buds. Once the plant has fully bloomed and the leaves have withered away, pull them from the garden if you are growing them as annuals. If you are growing a perennial form in a suitable growing zone, cut the plants back as short as you can for overwintering.

Propagating Nemesia

Nemesia is fairly easy to grow from seed (see below), but it can also be easily propagated by taking stem cuttings and rooting them:

1. In late summer, clip off four to six-inch cuttings from non-flowering shoots.
2. Dip the ends of the cuttings in rooting hormone, and plant them into small pots filled with commercial potting mix, lightly dampened.
3. Place the pot inside a plastic bag, then set it in a room temperature location until the cutting develops roots. Open the bag to ventilate if you notice moisture condensing on the plastic from the inside.
4. Once the cutting is rooted, remove the pot from the plastic and continue to grow it in a sunny location. Plant outside once all danger of frost has passed.

How to Grow Nemesia From Seed

Growing nemesia from purchased seed is a very effective and economical way to grow these plants. Use pots or trays filled with a commercial seed-starter mix or fine vermiculite. Dampen the spoil and place the containers in a location with indirect light at 55 to 65 degrees Fahrenheit. (The seeds need to be covered with soil to germinate.) You can expect the seeds to sprout in about five to 10 days. Continue growing them in bright light until planting time after danger of frost has passed. When the seedlings are about two inches tall, pinch out the growth tips to encourage a bushy growth habit.

Potting and Repotting Nemesia

Nemesias make good specimens for outdoor containers. Use a large, well-draining container. Ordinary peat-based potting mix is usually sufficient, although some gardeners like to blend in some additional sand, perlite, or vermiculite to improve drainage. It's also possible to use ordinary garden soil in containers, but there should be plenty of compost blended in.

Make sure to monitor potting mixture moisture and water whenever the top inch becomes dry to the touch.

Common Plant Diseases

There are no serious pest problems with nemesia, but root rot is a possibility where the plants are growing in dense, poorly drained soil. Root rot reveals itself when stems collapse at ground level. Less watering and a sunnier location can help prevent such rot.

Powdery mildew can also be a problem at times. Good air circulation and proper watering (soaking at the base of the plant rather than by overhead spraying) can prevent powdery mildew.

How to Get Nemesia to Bloom

These plants are rarely reluctant to bloom if they are growing in suitable conditions, but there are strategies to increase flowering and lengthen the bloom period:

• Feed with a water-soluble balanced fertilizer every two weeks to ensure maximum flowering.
• Deadheading by pinching off spent blossoms will prompt additional flowering, as well as keep the plant looking neat.
• In warm-weather regions, nemesia may respond well to being offered some shade during the heat of the day. In cooler zones, however, a lack of flowers may mean the plant is getting too little sun.
  
• If your plants do stop blooming, try cutting them back by about one-third to help bring them back into bloom.

Common Problems With Nemesia

Nemesia is free of most pest problems, but you may notice a few cultural issues:

Plants Are Scraggly

Trailing varieties of nemesia are especially prone to developing long, straggly stems without many flowers, especially if they are growing in a less-than-full-sun location. Radically cutting back the stems will prompt the plant to become more bushy and full. This treatment is especially useful for container plants and hanging baskets.

Plants Break Off at Ground Level

This is almost always a sign of root rot, a common problem if a plant is overwatered or forced to grow in dense, poorly draining soil. If you have poor soil, make sure it is amended to improve its porosity and drainage.

Plants Die Back in Summer

Don't immediately give up on nemesia plants that die back during the heat of summer. These plants do hate extreme heat, but if you radically cut them back and keep them well-watered, they often respond by rebounding and producing another flush of flowers in the fall.