Cultivation Techniques for Tulip Bulbs Treated at 9°C
Tulips require a certain period of cold treatment and will only flower after their stems have grown sufficiently. If tulip bulbs are cold-treated before normal winter, they can be brought into bloom earlier; this technique is called "forcing," and different treatments can make them flower between December and February of the following year. The bulbs first need transitional temperature treatment for varying periods before cold treatment begins. The transitional temperature refers to the temperature used from the time the flower has fully developed until the start of cold treatment; the duration of transitional temperature treatment depends on the cultivar and generally requires 2 to 8 weeks. 20°C is the optimal transitional temperature, as it benefits flower quality and root growth. The process of fully cold-treating dry bulbs for a certain period before planting is called the cold treatment process. Currently, tulip bulbs imported into China mainly fall into two major series: 9°C-treated and 5°C-treated bulbs. The effects of cold treatment are: shorter flower stems, larger flowers, faster bud and root development, and fewer flower diseases.
After understanding the treatment process for tulip bulbs, you can select bulbs with different treatments for cultivation. Below, the cultivation techniques are described in detail using 9°C-treated tulip bulbs as an example.
Bulb Source and Preparation: Tulip bulbs in China are mostly imported from the Netherlands. Every October, the cultivars to be planted must be selected and orders placed promptly. Bulbs are received at the end of October or beginning of November; after receipt, the bulbs are placed in a 5°C storage room for temporary storage.
Preparation of Seedling Beds: In a greenhouse, loam soil, peat, and farmyard manure are thoroughly mixed in a 4:1:1 ratio, then spread out and raked level to a thickness of about 10 cm, with a layer of coarse river sand about 5 to 7 cm thick spread on top. Strip-shaped seedling beds are generally no more than 3 m wide to facilitate later management. Disinfection and sterilization of the seedling beds should be carried out 10 to 15 days before sowing, generally using methyl bromide to disinfect the soil, or fumigants for treatment.
Sowing: Sowing time is generally between November 15 and December 15. Due to rooting problems and quality reduction, do not plant after December 15. Before sowing, peel the bulbs and then disinfect them. Soak the bulbs in a 0.2% carbendazim or 0.5% potassium permanganate aqueous solution for 10 to 15 minutes, then soak in clean water for 5 to 10 minutes; remove, air-dry, and sow. The sowing density is 8x12 cm, and the depth is such that about 1 to 2 cm of sand covers the top of the bulb. Water immediately after planting to prevent the bulbs from drying out and dehydrating.
Post-Sowing Management: Keep the soil moist to prevent the bulbs from drying out and dehydrating. Promptly replant into the sand layer any bulbs pushed out of the sand layer by root growth. Remove lateral buds. Control the day and night temperature in the greenhouse between 12°C and 22°C, with relative humidity not exceeding 80%. The greenhouse should be ventilated regularly. Keep detailed records of bulb growth conditions and greenhouse temperature, humidity, etc.
Diseases and Control
1. Damping-off: Flower stems or plants topple over. The cause is excessively high relative humidity in the greenhouse, or poor rooting of bulbs leading to reduced water uptake. Control methods: During management, do not allow excessively low temperatures, and do not let plants grow too rapidly in high temperatures; ensure normal root systems and avoid excessively high relative humidity (greater than 80%).
2. Blind buds: Flower buds lose water, petals remain green, leaf tips turn white, stamens and pistils dry up, and flowers cannot fully open. The causes are insufficient cold treatment, excessively high temperatures during storage and transport, excessively high relative humidity in the greenhouse, and improper watering methods leading to root suffocation, etc. Control methods: Strictly prevent the above phenomena at every stage.
3. Root rot: With mild infection, part of the root system rots; with severe infection, it causes flowers to wilt. Infected roots usually become waxy in appearance and turn the soil around the roots brown, and eventually the entire root system turns brown. The cause is infection by Pythium. Control methods: Disinfect the soil before planting. Promptly remove heavily infected bulbs. Ensure the greenhouse soil has good soil structure and a good drainage system. During the first two weeks after planting, keep the greenhouse temperature at 10°C or below.
4. Soft rot: In early infection, the infected bulb tissue softens, turns pink, and releases a peculiar odor; in later stages, soft rot manifests as stopped plant growth, yellowing leaf tips, and dehydration of flowers. The cause is infection by Pythium. Control methods: Fully disinfect and sterilize the bulbs before planting and disinfect the soil. Ensure the greenhouse soil has good soil structure and a good drainage system. Promptly remove infected plants and disinfect the affected soil.
5. Scorching: Water-soaked green spots appear on flowers and leaves, gradually becoming large white or brown spots; in severe cases, they can cause plants not to develop or hinder flowering. The cause is infection by Botrytis. Control methods: Remove already-infected bulbs before planting and disinfect the soil. Apply routine sterilization treatment to infected soil. During cultivation, keep plant leaves dry, especially at night. It is best to water directly onto the soil.