In this section, you will find the growing methods in use, the growing techniques, crop protection, disease control and variety choice of tulips, hyacinths and narcissus.

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14.18 Disorders: Oedema and hollow stems Immediately after bringing the plants into the greenhouse, they develop dark-green, watery patches that resemble frostbite. Thick drops of moisture are released in these damaged areas. In forcing, this phenomenon is known as “oedema”. As soon as a larger leaf surface permits greater evaporation, the plants will stop sweating, without any further problems. In the cultivars Monte Carlo and sports, Cassini, Snowstar and others, the symptoms may even occur up to two weeks after housing. During the rapid development of the plants a tear occurs lengthways in the stem which then develops into a hollow stem. The outside of the hollow stem contains small tears. Although the plant will flower, the bottom part of the stem is unusually thick and remains short. Although the hollow stems may occur in all tulip cultivars following frost damage, the two diseases only occur together in Monte Carlo and sports. Cause This typically physiological disorder occurs mainly in batches planted early (September/October). It seems there is slightly less risk during longer, warmer storage. Individual batches will vary greatly in their susceptibility to the disease. Plants that grow from the largest bulbs are particularly susceptible. The cause of the disorder is excessive water absorbtion combined with limited evaporation. Climatic conditions that hinder evaporation of the plants or bulbs stimulate the development of oedema and hollow stems. This is for example the case when humidity levels of the air and soil in the rooting room are too high. Batches that are buried in standing grounds and covered with straw are less susceptible and rarely suffer from these disorders. Planting soil is not normally used as this entails a higher risk of disease. After all, plants in this soil grow relatively more roots and the soil usually contains a great deal of moisture. Other factors that promote these disorders are the use of plastic trays and a high relative humidity. Laboratory research has shown that there is a connection between the material of the forcing trays (wood or plastic), the soil type and humidity. Control - Never use peat products as rooting substrate without mixing with 20% coarse-grain sand or potting soil. - If any glassy plants emerge, add 0.5 to 1.0 kg gr calcium nitrate per cubic metre substrate mixture or spread at least 50 gr calcium nitrate per square metre of tray surface area and water lightly. - Cover the tulips with a plastic sheet after housing them. - Stimulate the evaporation of the plants and maintain a relative humidity of no more than 75%.