This is a popular cool greenhouse plant, although perhaps not quite so popular now as in the time of my youth when it was much grown in theor conservatories on large estates. To grow browallias well, all that is needed is a frost-proof greenhouse and cultural attention as detailed below. There are both annual and perennial kinds.
Browallia demissa (syn. B. elata) is a half-hardy annual with bright blue or whitewhich it bears from early summer until late autumn. It makes a plant of about 1-1/2 ft. in height and is easily raised from seed sown in early spring. The rather taller B. speciosa major, a perennial, bears blue or violet flowers in summer and can also be raised from seed. It is extremely free flowering. Both can be brought into flower in winter by sowing seeds in July.
The seed should be sown thinly in boxes filled with seed compost and should be barely covered with fine compost. Germination takes place in a temperature of 16°C. (60°F.).
The seedlings are pricked out into 3-in. pots as soon as they are large enough to handle and moved on into 5-in. pots as they develop further. John Innes No. 1 Potting Compost suits them very well for both these stages. Also, it is possible to grow three plants of B. demissa in a 6-in. pot to provide large specimen plants. Place the pots in a light position.
Pinch out the tips of the shoots of Browallia speciosa major to ensure that they develop a bushy habit. This should be done when the plants are 3 to 4 in. high and the lateral branches are pinched out also after they have formed four or five leaves.