Nemesia, a plant genus from the Scrophulariaceae family, consists of annual, perennial, and sub-shrub plants that are indigenous to South Africa. Quite a few hybrids have been developed, with annual cultivars becoming popular bedding plants with gardeners.
They are generally treated as half-hardy plants in temperate regions, germinated from seed in warm areas, and transplanted outdoors when there is no danger of frost.
The genus comprises over 50 species, varying in height among different species from 8-24 inches high, with lance-shaped leaves growing in pairs on the stems. The wonderfully fragrant tubular flowers share a similarity with snapdragons and come in various shades of white, pink, red, orange, purple, violet, blue often with contrasting bicolored centers.
These plants can flower so profusely that they can almost obscure the leaves from spring to autumn when temperatures stay mild.
They are usually planted as garden-ready nursery plants in spring, although they are also easy to start from seeds. Gardeners in cold winters can directly sow seeds in spring into their gardens for a summer flowering season or start planting them indoors for spring flowering.
Gardeners in warm climates, where winters aren’t so cold, can directly sow seeds into their garden in autumn for flowers in winter.
When looking for nursery plants, choose seedlings with plenty of buds and just a couple of open flowers. These plants don’t transplant well, so selecting plants that haven’t yet flowered will reduce stress. When starting from seed, start the process 7 or 8 weeks before winter is predicted to end.
These plants grow best under full sunlight however, their flowering season might last longer, particularly in warm climates, if they can get some shade in the afternoon.
While it’s essential to keep their soil moist, be careful of over-watering too much water can lead to stem rot.
They don’t mind high humidity, although they might become more vulnerable to root rot and powdery mildew in very humid conditions. They grow well in cool and dry conditions if their soil moisture requirements are met.
They grow better in cooler temperatures. They prefer temperatures around 70°F during the day, with cooler temperatures at night – they might stop flowering if temperatures are over 70°F. They can bloom from spring until autumn in locations with milder temperatures in summer.
While they will grow better in spring or autumn in hot climates, they often die back a little in hot summers. These plants grow well as annuals in winter in warm regions.
They require soil that is moist but also well-draining. Soil rich in organic matter can be adjusted by adding vermiculite, perlite, or sand to improve drainage, using a multi-purpose peat-free compost with perlite or vermiculite added will ensure good drainage for potted plants. Raise pots or containers a little if they are sitting on a flat surface, so any excess water can freely drain away.
These plants don’t transplant or can be repotted successfully. Since these plants are annuals or short-living perennials, repotting is seldom required, only young seedlings can be repotted into their final home, either in your garden or in well-draining containers. Use a multi-purpose peat-free compost with perlite or vermiculite added to ensure good drainage
They are rather easy to grow from seeds, but they are also easily propagated from cuttings.
Propagation from seed
Growing these plants from purchased seeds is very easy and economical. Use trays or separate containers containing seed-starting mix or vermiculite. Moisten the soil, sow the seeds and cover them with soil and place the containers in a spot under indirect light at 55 – 65°F. Seeds usually sprout in about 5 – 10 days, move them under bright light until transplanting time. When the seedlings reach around 2 inches high, pinch away the growth tips – this encourages bushy growth.
Transplant the seedlings outdoors in your garden in spring, spaced about 4 – 6 inches apart or into large containers. Choose a sunny area or a partially shaded one in warmer climates with rich and moist soil and satisfactory drainage. Mulching will help protect the roots from hot or cold temperatures. Once they are established, these plants really won’t need much maintenance or care apart from keeping the soil moist.
Propagation by cuttings
In late summer, cut stems into 4 – 6-inch cuttings. Plant them individually into small pots full of slightly dampened potting mix. Place the pots inside separate plastic bags, then keep them under room temperature until rooting develops. Once the cuttings take root, remove them from the plastic bags and continue growing them in a sunlit location. Transplant them outdoors in spring or into large containers.
These plants need feeding just once in spring with a balanced slow-release fertilizer or you can use liquid fertilizer twice a month when they are growing actively.
Deadhead spent flowers to encourage the plants to produce new buds. Once flowering is finished and the leaves wither, remove the plants from the garden if you’re growing them like annuals. If you grow them as perennials, cut back the plants close to the soil line for overwintering.
These plants rarely stop flowering when they grow under suitable conditions, but there are some approaches to increase the production of flowers and stretch out the flowering period, feeding them with liquid fertilizer twice a month to increase flowering. Deadheading spent flowers also encourages more flowering.
In warm weather areas, they might respond well if offered some shade in hot afternoons. However, in cooler areas, they might not flower if they grow under shade. If they stop flowering, cut them down by about 1/3 which will help them start flowering again.
There are no major problems with pests, but root rot is often a risk when they grow in poorly draining soil. Root rot causes stems to collapse, reduce watering and move them to a sunny location, if possible to prevent root rot.
Powdery mildew can be a problem in areas of high humidity. Good air circulation with proper watering can prevent powdery mildew.
These plants might die back in hot summers. They don’t like extreme heat, but radically cut them down about 1/3, and keeping them well-watered will help them rebound and produce another flowering period in autumn.