How to Grow Viola cornuta and Things to Watch Out For

Viola cornuta has 900-1500 seeds per gram. It is suitable for sowing with a precision seeder. The optimum temperature for seed germination is 15°C-20°C; about 7-14 days are needed for seedlings to emerge after sowing. Once the seedlings emerge, they should be exposed to light immediately, otherwise they easily become leggy seedlings.

Viola cornuta has relatively small cotyledons and can be raised in 200-cell plug trays with a pH of 5.2-6.2. The suitable sowing medium is a 1:1 mix of peat and perlite. Mixing a 700-fold dilution of chlorothalonil into the medium can effectively prevent seedling-stage diseases. Fresh seeds harvested the previous year generally have a germination rate above 90%, so only 1 seed needs to be sown per cell, and the medium covering the seed after sowing should be roughly as thick as the seed diameter. Immediately after emergence, lower the day/night temperature to 18°C/14°C to prevent the seedlings from growing leggy. After true leaves appear, 50-75 ppm nitrogen fertilizer can be applied, and as the seedlings grow, the nitrogen concentration can be gradually increased to 100 ppm. The medium should always be kept moist during the seedling-raising period. At 4-5 weeks after sowing, when there are 4-5 true leaves, they can be transplanted into 8 cm pots or planted out.

In the middle and lower reaches of the Yangtze River in China, sowing can be done in mid-to-late September, and the plants can be placed or planted out in the open field in late November; by December they can bloom and form a landscape display. In northern regions, seeds can be sown and seedlings raised in a greenhouse in January-February, and a landscape display can begin to form in the open field in March-April. If cooling equipment is available in summer, seedlings can also be raised in summer and bloom in autumn. 

For growing Viola cornuta, choose a sandy loam with high organic matter content, good drainage and a pH of 5.6-6.5. During the post-transplant recovery period, the soil should always be kept moist, and fertilizing can begin only after the plants have recovered. At this point the flower buds of Viola cornuta begin to differentiate and the plants gradually enter the reproductive growth stage. In addition to nitrogen fertilizer, potassium fertilizer is also needed, with a ratio of nitrogen to potassium oxide of 1:1.5. Viola cornuta is relatively sensitive to fertilizer concentration, which generally should not exceed 150 ppm; growth is poor when the soil salt content is above 1.5 g/L. After the plants enter the vigorous growth stage, liquid fertilizer can be applied weekly according to the above requirements. Among trace elements, Viola cornuta has a relatively high demand for Mg and Fe; during the growing period, 0.025 g/L MgSO4 and FeSO4 can be sprayed 1-2 times. Pinching during the growing period can promote side branches, increase the number of flowers per plant and extend the flowering period of a single plant. Reasonable use of growth retardants such as paclobutrazol helps form a compact plant shape.