Tulips (Tulipa) form a genus of spring-blooming perennial herbaceous bulbiferous geophytes (having bulbs as storage organs). The tulip is a member of the Liliaceae (lily) family, along with 14 other genera, where it is most closely related to Amana, Erythronium and Gagea in the tribe Lilieae. There are about 75 species, and these are divided among four subgenera. The name “tulip” is thought to be derived from a Persian word for turban, which it may have been thought to resemble. Tulips originally were found in a band stretching from Southern Europe to Central Asia, but since the seventeenth century have become widely naturalised and cultivated. In their natural state they are adapted to steppes and mountainous areas with temperate climates. Flowering in the spring, they become dormant in the summer once the flowers and leaves die back, emerging above ground as a shoot from the underground bulb in early spring.
In the seventeenth century Netherlands, during the time of the Tulip mania, an infection of tulip bulbs by the tulip breaking virus created variegated patterns in the tulip flowers that were much admired and valued. While truly broken tulips do not exist anymore, the closest available specimens today are part of the group known as the Rembrandts – so named because Rembrandt painted some of the most admired breaks of his time.[
Breeding programs have produced thousands of hybrid and cultivars in addition to the original species (known in horticulture as botanical tulips).
The genus, which includes about 75 species, is divided into four subgenera.
- Clusianae (4 species)
- Orithyia (4 species)
- Tulipa (52 species)
- Eriostemones (16 species)
|Tulipa × gesneriana|
Diseases and Problems
Botrytis tulipae is a major fungal disease affecting tulips, causing cell death and eventually the rotting of the plant. Other pathogens include anthracnose, bacterial soft rot, blight caused by Sclerotium rolfsii, bulb nematodes, other rots including blue molds, black molds and mushy rot. The fungus Trichoderma viride can infect tulips, producing dried leaf tips and reduced growth, although symptoms are usually mild and only present on bulbs growing in glasshouses.
In horticulture, tulips are divided into fifteen groups (Divisions) mostly based on flower morphology and plant size.[
- Div. 1: Single early – with cup-shaped single flowers, no larger than 8 cm across (3 inches). They bloom early to mid season. Growing 15 to 45 cm tall.
- Div. 2: Double early – with fully double flowers, bowl shaped to 8 cm across. Plants typically grow from 30–40 cm tall.
- Div. 3: Triumph – single, cup shaped flowers up to 6 cm wide. Plants grow 35–60 cm tall and bloom mid to late season.
- Div. 4: Darwin hybrid – single flowers are ovoid in shape and up to 8 cm wide. Plants grow 50–70 cm tall and bloom mid to late season. This group should not be confused with older Darwin tulips, which belong in the Single Late Group below.
- Div. 5: Single late – cup or goblet-shaped flowers up to 8 cm wide, some plants produce multi-flowering stems. Plants grow 45–75 cm tall and bloom late season.
- Div. 6: Lily-flowered – the flowers possess a distinct narrow ‘waist’ with pointed and reflexed petals. Previously included with the old Darwins, only becoming a group in their own right in 1958.
- Div. 7: Fringed (Crispa) – cup or goblet-shaped blossoms edged with spiked or crystal-like fringes, sometimes called “tulips for touch” because of the temptation to “test” the fringes to see if they are real or made of glass. Perennials with a tendency to naturalize in woodland areas, growing 45–65 cm tall and blooming in late season.
- Div. 8: Viridiflora
- Div. 9: Rembrandt
- Div. 10: Parrot
- Div. 11: Double late – Large, heavy blooms. They range from 18 to 22 inches tall.
- Div. 12: Kaufmanniana – Waterlily tulip. Medium-large creamy yellow flowers marked red on the outside and yellow at the center. Stems 6 in. tall.
- Div. 13: Fosteriana (Emperor)
- Div. 14: Greigii – Scarlet flowers 6 in. across, on 10 in. stems. Foliage mottled with brown.
- Div. 15: Species or Botanical – The terms “species tulips” and “botanical tulips” refer to wild species in contrast to hybridised varieties. As a group they have been described as being less ostentatious but more reliably vigorous as they age.
- Div. 16: Multiflowering – not an official division, these tulips belong in the first 15 divisions but are often listed separately because they have multiple blooms per bulb.
They may also be classified by their flowering season:
- Early flowering: Single Early Tulips, Double Early Tulips, Greigii Tulips, Kaufmanniana Tulips, Fosteriana Tulips, § Species tulips
- Mid-season flowering: Darwin Hybrid Tulips, Triumph Tulips, Parrot Tulips
- Late season flowering: Single Late Tulips, Double Late Tulips, Viridiflora Tulips, Lily-flowering Tulips, Fringed (Crispa) Tulips, Rembrandt Tulips
A number of names are based on naturalised garden tulips, and are usually referred to as neo-tulipae. These are often difficult to trace back to their original cultivar, and in some cases have been occurring in the wild for many centuries. The history of naturalisation is unknown, but populations are usually associated with agricultural practices and are possibly linked to saffroncultivation . Some neo-tulipae have been brought into cultivation, and are often offered as botanical tulips. These cultivated plants can be classified into two Cultivar Groups: ‘Grengiolensis Group’, with picotee tepals, and the ‘Didieri Group’ with unicolourous tepals.
Because of the fact that tulip bulbs don’t reliably come back every year, tulip varieties that fall out of favor with present aesthetic values have traditionally gone extinct. Unlike other flowers that do not suffer this same limitation, the Tulip’s historical forms do not survive alongside their modern incarnations.
Tulip bulbs are typically planted around late summer and fall, in well-drained soils. Tulips should be planted 4 to 6 inches (10 to 15 cm) apart from each other. The recommended hole depth is 4 to 8 inches (10 to 20 cm) deep, and is measured from the top of the bulb to the surface. Therefore, larger tulip bulbs would require deeper holes. Species tulips are normally planted deeper.
Tulip growth is also dependent on temperature conditions. Slightly germinated plants show greater growth if subjected to a period of cool dormancy, known as vernalisation. Furthermore, although flower development is induced at warmer temperatures (20–25 °C), elongation of the flower stalk and proper flowering is dependent on an extended period of low temperature (<10 °C). Tulip bulbs imported to warm-winter areas are often planted in autumn to be treated as annuals. The colour of tulip flowers also vary with growing conditions
Tulips can be propagated through bulb offsets, seeds or micropropagation. Offsets and tissue culture methods are means of asexual propagation for producing genetic clones of the parent plant, which maintains cultivar genetic integrity. Seeds are most often used to propagate species and subspecies or to create new hybrids. Many tulip species can cross-pollinate with each other, and when wild tulip populations overlap geographically with other tulip species or subspecies, they often hybridise and create mixed populations. Most commercial tulip cultivars are complex hybrids, and often sterile.
Offsets require a year or more of growth before plants are large enough to flower. Tulips grown from seeds often need five to eight years before plants are of flowering size. To prevent cross pollination, increase the growth rate of bulbs and increase the vigor and size of offsets, the flower and stems of a field of commercial tulips are usually topped using large tractor-mounted mowing heads. The same goals can be achieved by a private gardener by clipping the stem and flower of an individual specimen. Commercial growers usually harvest the tulip bulbs in late summer and grade them into sizes; bulbs large enough to flower are sorted and sold, while smaller bulbs are sorted into sizes and replanted for sale in the future.