The only vegetative reproductive organ of freesias is the corm. Its shape depends on the age and characteristics of the variety. Stage-younger corms, such as those grown from children, are longer than older ones. Diploid varieties tend to have flatter and rounder tubers than polyploid varieties. Among the polyploid varieties, only Princess Marijke and Pimpernel have rounded tubers with 1-3 vegetative buds. Most of the other varieties have elongated, conical tubers with only one apical bud. Dormant buds start to grow when the central bud is removed or its growth is suppressed by chemical or physical means.
K. Kukulčanka has tested 27 different physical and chemical measures and found that only a few of them can suppress apical growth. The growth inhibitors entilenchlorhydride and melenoic acid hydrate had this effect. When apical growth was inhibited by these agents, lateral dormant buds started to grow. This resulted in more corms being produced.
About 42 % of the weight of the tubers is water. Carbohydrates are the main part of the dry matter. 5-7 % of the absolute dry matter is made up of macronutrients: nitrogen, phosphorus, potassium.
Freesias grown outdoors are quite hardy if grown in unfertilised soil. In greenhouses, they will warp and deform very quickly, so it is necessary to tension the nets. Autumn-grown freesias usually need 3 rows of netting, while winter-grown freesias only need 2. Some very tall varieties, such as Margaret, may need as many as four rows.
The first net should be set at a height of 10 cm and the second at 15 cm above the first. The mesh size is 10 × 10 cm. It is very important that the nets are well tensioned, are not made of coarse material and do not block the light. The nets can be arranged in the same way as for carnations.
Spraying with chemicals
In greenhouses, freesias are very badly attacked by aphids. These pests not only damage and deform the plants, but also transmit viruses. The plants are therefore sprayed against diseases and pests during the growing season. If they are healthy, spraying should start 2 months after planting and even earlier if signs of disease are evident. Spray every 10-15 days with one of the systemic fungicides (0.1% benlate, 0.1% fundasol, 0.1% topsin, 0.1% BMK), mixed with an insecticide (0.15% rogor, 0.2% antio or 0.2% fozalone). When spraying, the greenhouse temperature should be raised above 20 °C as fungicides do not work well when it is cold. All pesticides are harmful to the flowers of freesias, so do not spray the plants while they are flowering.
Special features of cultivation
Freesia seeds are medium sized. Their size depends on the colour of the flowers. There are 85-90 yellow-flowered, 95-110 red-flowered, 105-110 white-flowered and 120-124 blue-flowered freesia seeds per gram. Sow 2 to 3 grams of yellow-flowered freesia seeds per square metre or 1.5 to 2.5 grams of other colours.
Diploid varieties germinate quickly, while tetraploid varieties need to be stimulated by rubbing the seeds between sandpaper or soaking them in water at 20 °C for a day, or simply by lightly tapping them. Often the seeds are germinated in moist vermiculite or peat and covered with black polythene film. Maintained at a temperature of 20-22 °C. Germination takes 5-10 days. When small sprouts have emerged, the seeds are sown. If germination is not simultaneous, sow several times.
The number of seeds that germinate is highly dependent on temperature. The optimum germination temperature is said to be 20 degrees (about 95 % germination). At 30 °C about 20 % germinate. At 12 °C only about 30 %.
Yellow-flowered freesias germinate twice as fast as red-flowered or blue-flowered ones. Seeds germinate fastest when sown when just ripe, although they remain germinable for 2-3 years. Seeds with a germination energy of less than 80 per cent are considered unsuitable.
They can be sown simply in a permanent location or transplanted when the root is no longer than 0.5 cm. Sow about 2.5 g of seed per square metre of land. Approximately 200 plants germinate. Can be sown in peat pudding or polythene pots (4 seeds per pot), or in standard pitching boxes with higher sides. The peat moss and polyethylene cups are then placed in containers filled with soil. In England, 18-19 seeds are sown in 22 cm diameter pots, followed by 12-14 plants. Sow 0.5-1 cm deep and cover with a 2 cm layer of peat. After germination, the temperature is maintained at 13-15 °C.
In Denmark, research has been carried out on the best density at which to grow seed freesias. It was found that this depends on the growing period. When sowing seeds, it is best to grow 250 plants per square metre in February and 130 in June. In the former case, the plants are spaced every 4 cm in the row, in the latter case every 7-8 cm, leaving 10 cm spacing. Later sowing, in warm weather, results in twice as many leaves as when sown in colder weather.