Once the frosts are over, seed freesias should be taken outside immediately, as it is cooler outside in summer than in the greenhouse. Intense light does not harm freesias, but they need to be shaded to reduce the ambient temperature.
The area where the freesia will be placed should be lined with plastic sheeting to prevent the roots from taking root and being damaged when they are taken back to the greenhouse.
The soil must be light and friable. Neutral reaction moss peat is very suitable. Freesias are said to germinate very well when sown in a mixture of 3 parts moss peat and 1 part sand. The best soil for permanent growth is a mixture of equal parts moss peat and sand.
The soil must be fertilised before sowing, but only sparingly (100g of potassium nitrate per cubic metre, 150g of potassium sulphate or calimagnesia, 1200g of simple superphosphate, 5kg of chalk). Small amounts of fertiliser are difficult to mix and should be mixed first with sand and then with soil.
Additional fertiliser should be applied early, i.e. 5-6 weeks after sowing. Initially, fertiliser should be applied every 10 days, and if the growth is poor, fertiliser should be applied weekly.
The main fertiliser is nitrogen and potassium fertiliser (10-20 g mineral salts per 10 litres of water). One or two applications of micronutrients. The ratio of nitrogen to potassium should be 2:1 when the plants are outdoors and 1:1 when they are brought into the greenhouse. This is the ratio when a mixture of equal parts of ammonium and potassium nitrates is made. In autumn, when the weather is cloudy, only potassium nitrate is fertilised, alternating with calcium nitrate.
Seed freesias therefore require more fertiliser than those grown from tuberous tubers, which are rich in nutrients.
In greenhouses, seed freesias are treated in the same way as those grown from tubers.
Flowering takes place 9-12 months after sowing.
The yield of freesia seeds is highly dependent on the temperature at the time of cultivation.
The highest seed set occurs at a temperature of 20 °C when the plants are in flower and at 14 °C before flowering. There are about 10 to 12 seeds per seed box. The maximum number of seeds that can be collected per plant is about 100, i.e. about 1 g.
It is advisable to reproduce tubers from seed for up to 4 years.
Planting depth and position of tubers
The planting depth and the position of the freesia tubers (upright, upside down or bottom up) did not have a significant effect on the yield of flowers and tubers. This was investigated by the Danish scientist H.E. Kresten-Jensen in 1969, planting the tubers at a depth of 2, 5 and 8 cm, and by the Polish scientist K. Kukulčanka in 1974, planting them at a depth of 4, 8, 12 and 16 cm. The latter found that even shallowly planted tubers were found deeper when dug up, being drawn in by the drying contractile roots.
We plant the tubers at a depth of 6 cm. When planted at this depth, the plants grow quite firm and do not dry out as quickly. In various soil mixtures they should be planted at a depth of 4 cm. In summer, plant at a depth of 8 cm. At this depth, the soil temperature is lower and the plants develop faster.
The planting density of freesias depends on a number of factors: light, fungal diseases, size of the corms and cultivar characteristics.
Plants become very thin and flabby if light cannot reach the lower part of the plant. This is why freesias should be planted less frequently in autumn when there is little sun. In summer, tuber crops should also be planted less frequently, as more leaves are produced.
When freesia cultivation first started, 150-200 tubers per square metre used to be planted, but this was later reduced to 100, because dense planting resulted in higher incidence of fungal diseases, fewer flowers and smaller tubers.
Now there are again articles in the literature stating that the total income per flower is higher when planting up to 200 plants per square metre. This is because fewer plants are suffering from fungal diseases as a result of the discovery of more effective chemical preparations.
Larger corms are planted less frequently, smaller ones more densely.
Different varieties of corms produce different numbers of offspring and also have different leaf sizes. Therefore, all freesia catalogues specify how many varieties of corms should be planted per square metre.
Blauwe Wimpel, Saffier, Stockholm, Souvenir are the most densely planted varieties at 110-130 per square metre, while Margaret, Pimpernel, Princess Marijke, Rosita, Rosemunde are planted at 100-110 corms per square metre.
The least frequently planted varieties are Royal Gold, Eldorado, Appolo, Ballerina, Gloria Solis, Copenhagen, Rose-Marie, Sonata, with 80-100 tubers per square metre.
Freesias are usually planted in rows spaced 10 centimetres apart. On some farms, freesias are planted at 12.5-15 cm row spacing and more densely in rows. This allows more light to reach the lower part of the plant.