Using flower bulbs in gardens and parks


When using flower bulbs in gardens and parks, it is important to know whether the bulbs will perform as annuals or perennials. To find out more about this, the IBC and Applied Plant Research (PPO) conducted a study on the perennial flowering of flower bulbs


There are still many questions about whether flower bulbs should be seen as annual or perennial plants. Since almost all summer-flowering bulbous, cormous and tuberous plants such as dahlias, gladioli and begonias originate from tropical or subtropical regions, they can tolerate no frost at all and can thus be treated as annuals. The exceptions to this rule are lilies, crocosmias, anemones and many other special bulbous plants that can indeed perform as perennials in our temperate climate. All the autumn-flowering cormous and tuberous plants (colchicums, autumn-flowering crocuses, cyclamens) will perform as perennials, so the only other bulbs to be categorised as ‘perennials or annuals’ are the spring-flowering bulbs such as the tulips, hyacinths, daffodils, etc.

A range of factors
It’s impossible, however, to provide a simple answer to this question because so many factors are involved in determining annual or perennial flowering. The first of these involves the species’ natural habitat. Many bulbous plants originally come from regions with cold winters and hot summers; these are the conditions under which the bulbs will grow and flower best. Some bulbous plants, such as scillas, daffodils, and hyacinthoides, can tolerate a certain amount of shade, but most species prefer full sun. Light and warm temperatures are especially important during the period immediately flowering. These conditions ensure that the leaves can produce sufficient carbohydrates, important nutrients for the embryo that becomes the mature bulb that will flower next year. A period of light lasting four to six weeks is needed after flowering to provide the embryo with nutrients; if this condition is not met because the location is too shady, the bulb will produce only leaves next year and no new flowers. It should thus be obvious that the leaves play an important role in the development of the bulb, which is why it is so important not to trim them off, but rather to leave them undisturbed until they are completely desiccated. The faded flower (but not the flower stem) should be removed in order to prevent the production of seeds.

The same bulbous plants prefer a warm summer location. Bulbs planted too deeply (where they will not receive enough of this heat) will develop poorly. The same effect (not enough summer heat) is achieved by automatic sprinklers: they can have a fatal impact on bulbs that require hot, dry conditions. Planting not deeply enough can be just as disastrous: the bulbs will dry out and then fail to flower.
This is why it is advisable to plant spring-flowering bulbous plants in combination with perennials whenever possible; as a second layer among the perennials, they benefit from this protection. Finally, the provision of fertiliser is another determining factor for the perennial flowering of spring-flowering bulbous plants. Applying an organic, slow-release fertiliser when the noses of the bulbs have just emerged from the ground will ensure that these nutrients become available once flowering is almost over – and this is exactly when the bulb requires these nutrients. Following with these guidelines has shown that bulbs previously thought to perform as annuals can actually perform as perennials for a number of years. Not just daffodils, but also tulips cultivars such as 'Candela’, 'Cape Cod’, 'Yokohama', 'Negrita' and 'Parade' are very suitable for perennial flowering. And hyacinth cultivars such as ‘Pink Pearl’, ‘White Pearl’ and ‘Delft Blue’ can also play an important role.

More information can also be found in our 'Landscaping brochure'.
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