Sow, 1 seed/plug (180-384 tray), at 15°C-18°C. High temperatures reduce the germinating power.Humidity: 95%
Sow in a well-drained, light substrate with a low nutrient state (EC=100µS/cm) and a pH of 5.8. Cover the seeds with vermiculite to avoid direct sunlight and too dry conditions. 10-12 days in a germination room is possible.
Pot the plants after 6-8 weeks (384-180 tray) in a well-drained Primula mixture, pH 5.8, EC=300µS/cm. Use a mixture based on peat with 5-10% clay, eventually with some perlite for good drainage. Extra micro-nutrients and iron are advised.
Pot the plugs well-watered. Water abundantly after potting, especially in full sun to avoid burning of the foliage.
Keep the greenhouse as cool as possible for qualitative growth. This means with open windows resulting in a healthy and active crop. Shade at high irradiance.
When potting late, from week 40 on, a minimum of 12°C is necessary for a quick start until the plant is well formed, minimum 6 true leaves. This is important for later bud initiation.
Outside potting is beneficial for extra early and uniform flowering. New varieties need little cold and can be potted inside.
Most primrose varieties can withstand frost (except for example ‘Zebra’). Plants must be de-frozen slowly. Make sure the plants are well watered before frost. Plants can be damaged when de-frozen too fast, for example at high irradiance. Be careful with CO2-burners. Leaf damage is common. Use a burner with a chimney to take no risk.
Increase temperature till 10 - 12°C (only if the flower bud is present!). High temperatures are discouraged to avoid stretching of the flower buds and crop. Ideal is to use a cold greenhouse for production and a warmer greenhouse for forcing.
Plants with slight flowering buds can be stored in a refrigerator at 0.5°C for 4 weeks.
Give pure water after potting.
If you seed roots outside the root ball, start fertilising with a complete fertiliser like (N-P-K) 15-5-30 at 2.2 EC. When the root ball is well developed it can be necessary to fertilise with 4 EC and to rinse off afterwards. Check the conductivity in the pot to fertilise as necessary. The times you need to water depends of the weather, resulting in different conductivities in the pot (target 400µS/cm, 1/5 method).For vigorous varieties it can be necessary to use (N-P-K) 12-12-36.Use 19-6-20 for compact varieties or even calcium nitrate to get the right plant size, especially for bigger pot sizes.Also when planted late more nitrogen is advised to produce enough foliage in a short time. Grow them damp in the pot.During flowering it is advised to use ebb and flood to avoid flower damage. Fertilise during the whole crop time for excellent plant quality.
For a good plant habit:-grow them dry and use growth regulators such as Alar (B-nine) / Caramba / Regalis / Carax where available.The dose varies from the climate and the variety. Genetic compact varieties like ‘Tobie’ need no growth regulator under normal conditions.
Chlorosis, Cell burst, Spider mite, Trips, Aphids, Leaf miner, Caterpillar, White fly, Botrytis, Real mildew, Ramularia or leaf spot disease, Mycocentrospora, Bacteria
The information and advice on cultivation provided on this pages has been compiled with the utmost care. Nevertheless we should point out that growers must apply this advice in accordance with their own knowledge and understanding. In the event of uncertainty, we advise that trials should first be carried out to establish the influence of local conditions. Rudy Raes Bloemzaden NV is not liable for the information provided in these publications.
Basic material from plant varieties that are protected by a plant breeders rights must not be used for propagation. Varieties thus protected are indicated by Rudy Raes Bloemzaden nv by an R or TM. Errors shall give rise to a penalty charge for each additional plant.