Tulip (Tulipa)

Tulips are flowering members of the lily family and are some of the most widely cultivated ornamental plants in the world. Their large, showy, cup-shaped blossoms have for centuries been associated with beauty and elegance. These plants were also at the heart of what is often considered to be the first speculative bubble in history, when in the mid-17th century, “Tulip-mania” gripped the Netherlands. It was a market frenzy that sent the prices of tulip bulbs skyrocketing to the point where they were used as a currency. Today, the Netherlands is still famous for its huge and stunningly colorful tulip fields.

I. Appearance and Characteristics

Tulips are spring-blooming perennial herbaceous bulbiferous geophytes in the Tulipa genus. Their flowers are usually large, showy, and brightly coloured, generally red, orange, pink, yellow, or white. They often have a different coloured blotch at the base of the tepals, internally. Because of a degree of variability within the populations and a long history of cultivation, classification has been complex and controversial. The tulip is a member of the lily family, Liliaceae, 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 by those who discovered it. Tulips were originally found in a band stretching from Southern Europe to Central Asia, but since the seventeenth century have become widely naturalised and cultivated.

Tulips are perennial herbaceous bulbiferous geophytes that bloom in spring and die back after flowering to an underground storage bulb. Depending on the species, tulip plants can be between 10 and 70 cm (4 and 28 inches) high.

Tulip stems have few leaves. Larger species tend to have multiple leaves. Plants typically have two to six leaves, some species up to 12. The tulip’s leaf is cauline (born on a stem), strap-shaped, with a waxy coating, and the leaves are alternate (alternately arranged on the stem), diminishing in size the further up the stem. These fleshy blades are often bluish-green in colour. The bulbs are truncated basally and elongated towards the apex. They are covered by a protective tunic (tunicate) which can be glabrous or hairy inside.

• Flowers

The tulip’s flowers are usually large and are actinomorphic (radially symmetric) and hermaphrodite (contain both male (androecium) and female (gynoecium) characteristics), generally erect, or more rarely pendulous, and are arranged more usually as a single terminal flower, or when pluriflor as two to three (e.g. Tulipa turkestanica), but up to four, flowers on the end of a floriferous stem (scape), which is single arising from amongst the basal leaf rosette. In structure, the flower is generally cup or star-shaped.

As with other members of Liliaceae the perianth is undifferentiated (perigonium) and biseriate (two whorled), formed from six free (i.e. apotepalous) caducous sepals arranged into two separate whorls of three parts (trimerous) each. The two whorls represent three petals and three sepals, but are termed tepals because they are nearly identical. The petals are usually petaloid (petal-like), being brightly coloured, but each whorl may be different, or have different coloured blotches at their bases, forming darker colouration on the interior surface. The inner petals have a small, delicate cleft at the top, while the sturdier outer ones form uninterrupted ovals.

The flowers have six distinct, basifixed introrse stamens arranged in two whorls of three, which vary in length and may be glabrous or hairy. The filaments are shorter than the tepals and dilated towards their base. The style is short or absent and each stigma has three distinct lobes, and the ovaries are superior, with three chambers.

Tulip flowers come in a wide variety of colors, except pure blue (several tulips with “blue” in the name have a faint violet hue), and have absent nectaries. Tulip flowers are generally bereft of scent and are the coolest of floral characters. The Dutch regarded this lack of scent as a virtue, as it demonstrates the flower’s chasteness.

While tulips can be bred to display a wide variety of colors, black tulips have historically been difficult to achieve. The Queen of the Night tulip is as close to black as a flower gets, though it is, in fact, a dark and glossy maroonish purple – nonetheless, an effect prized by the Dutch. The first truly black tulip was bred in 1986 by a Dutch flower grower in Bovenkarspel, Netherlands. The specimen was created by cross-breeding two deep purple tulips, the Queen of the Night and Wienerwald tulips.

• Fruit

The tulip’s fruit is a globose or ellipsoid capsule with a leathery covering and an ellipsoid to globe shape. Each capsule contains numerous flat, disc-shaped seeds in two rows per chamber. These light to dark brown seeds have very thin seed coats and endosperms that do not normally fill the entire seed.

• Phytochemistry

Tulipanin is an anthocyanin found in tulips. It is the 3-rutinoside of delphinidin. The chemical compounds named tuliposides and tulipalins can also be found in tulips and are responsible for allergies. Tulipalin A, or α-methylene-γ-butyrolactone, is a common allergen, generated by hydrolysis of the glucoside tuliposide A. It induces a dermatitis that is mostly occupational and affects tulip bulb sorters and florists who cut the stems and leaves. Tulipanin A and B are toxic to horses, cats and dogs. The color of a tulip is formed from two pigments working in concert; a base color that is always yellow or white, and a second laid-on anthocyanin color. The mix of these two hues determines the visible unitary color. The breaking of flowers occurs when a virus suppresses anthocyanin and the base color is exposed as a streak.

• Fragrance

The great majority of tulips, both species and cultivars, have no discernable scent, but a few of both are scented to a degree, and Anna Pavord describes T. Hungarica as “strongly scented”, and among cultivars, some such as “Monte Carlo” and “Brown Sugar” are “scented”, and “Creme Upstar” “fragrant”.

Tulips are indigenous to mountainous areas with temperate climates, where they are a common element of steppe and winter-rain Mediterranean vegetation. They thrive in climates with long, cool springs and dry summers. Tulips are most commonly found in meadows, steppes and chaparral, but also introduced in fields, orchards, roadsides and abandoned gardens.

II. How to Grow and Care

Sunlight

All varieties of tulips prefer full sun. Remember, the areas under deciduous trees are shady in the summer and mostly sunny in the early spring when tulips are actively growing. Thus, these spaces are excellent spaces for growing tulips and other spring bulbs.

Temperature and Humidity

Tulips thrive in regions with cool-to-cold winters and dry, warm summers—conditions found through much of USDA zones 3 to 8. They require 12 to 14 weeks of temperatures below 55 degrees Fahrenheit to bloom, so in regions with warm winter temperatures, they must be planted as annuals from suppliers who prechill the bulbs.

Tulips tend to do better in dry regions rather than humid climates since high humidity usually goes hand-in-hand with lots of spring and summer rain, which can cause bulbs to rot.

Watering

Water the bulbs thoroughly immediately after you plant them, but withhold watering after this except during extended dry spells. If your region gets rain every week or two, don’t water your tulips. In arid regions, watering every two weeks is recommended.

Soil

Tulips prefer rich, well-draining soil with a neutral pH to slightly acidic (6.0 to 7.0). Mixing in compost can improve drainage and provide nutrients to the bulbs. Ideally, do this before planting the bulbs. Otherwise, you can apply a few inches of compost over the soil to encourage earthworms to tunnel into the soil, improving circulation and tilth.

Fertilizing

Add some compost, bone meal, or granular fertilizer to the planting hole when you plant the tulip bulbs. Feed them again the following spring when they sprout again. Other than this, no additional feeding is necessary. For the amount to use, follow the product label instructions.

Planting Instructions

Tulips grow best as perennials in climates with moist, cool-to-cold winters and warm, dry summers. Because they sprout and bloom early in the spring, tulips can work well beneath trees and shrubs that will leaf out to create shady conditions later in the season.

Plant the bulbs 4 to 8 inches deep in the fall (a depth about three times the size of the bulbs) in a sunny location with well-drained soil. Space the bulbs 2 to 5 inches apart (depending on their size), with the pointy end facing up. Tulips tend to display best if planted in groups of about 10 bulbs.

Tulips are sometimes grown as annuals—especially the hybrid varieties. Unless labeled as “perennialized” or “naturalizing,” hybrids rarely rebloom the following year. If it’s not a reblooming type, dig them up and discard the bulbs after blooming is complete. Reblooming hybrid types must be divided every few years to keep them from declining.

Pruning

When growing tulips as perennials, remove the flower stalks immediately after they flower to prevent the plants from producing seed pods, which drains the bulb’s energy and shortens its life. Leave the foliage in place until it turns yellow in mid-to-late summer. This helps replenish the bulb’s energy.

Propagation

Tulips spread in two ways: by creating bulblets that sprout from the mother bulb underground and by seeds produced by flowers. The most common (and quicker method) is lifting the bulbs and dividing the offset bulbs (bulblets) attached to the mother bulb. This should be done in the fall, at the normal planting time for tulips. Divide bulbs every three to five years.

• Dig up the bulbs with a trowel or spade, then brush off the soil and gently break off the small offset bulbs from the mother bulb.
• Inspect the offsets and discard any that appear soft or deformed.
• Replant the offsets and the mother bulb at a depth about three times the bulb’s diameter, with the pointed side facing up.
• The new tulips may produce foliage but no flowers for the first few years. At about the third year, you can expect the new bulbs to bloom.

How to Grow from Seed

Propagating tulips by seeds is uncommon, as they are very slow-growing, and seeds collected from hybrid plants generally do not “come true” to the original plant.

However, species tulips (not hybrids) will come true if you plant the seeds found in the pods left behind after the flowers fade. But nursing the seeds through germination to mature plants with bulbous roots is a slow process, requiring at least two years.

• After collecting the seeds from the dried pods, store them in the refrigerator for at least 12 to 14 weeks. In cold winter zones, tulip seeds are often planted indoors in late February.
• Sow tulip seeds on the surface of small pots filled with potting mix. Cover the seeds with a bare covering of additional potting mix (1/4 inch).
• Place the pots in a sunny location and keep them moist until the seeds sprout.
• Keep the seedlings growing in the pot through the spring, summer, and fall, feeding them weekly with a half-strength dose of balanced 10-10-10 fertilizer. Heavy feeding is necessary for the seedlings to create bulbous roots. The pots can be moved outside once the weather warms.
• In late fall, move the potted plants into a refrigerator or a cold frame for outdoor chilling. The plants will need to be chilled for at least 12 weeks.
• After the chilling period is complete in later winter or early spring, bring the pots back outdoors to sprout and grow again.
• Once the foliage is fully developed in this second growing season, the plants can be transplanted into their permanent garden locations.
• Remain patient; it may take another year before seed-started plants can flower.

Potting and Repotting

Tulips are easy to grow in well-draining pots filled with standard potting mix. This method is often used to force tulips into midwinter bloom indoors, but timing is critical, as the bulbs require a 12- to 14-week chilling period.

Plant the chilled bulbs about 2 to 3 inches deep, lightly moisten the soil, then store the pots in a dry, cool (35 to 55 degrees Fahrenheit) location for the recommended chill period. The pots can be chilled in a refrigerator or outdoors in a sheltered area if you live in a cold-winter climate.

After the chill period, bring the pots into a bright room at moderately warm temperatures—about 60 to 65 degrees. Within three to five weeks, the plants should flower. Thus, the bulbs must be planted in late September and chilled until late December for late January or early February bloom.

Potted bulbs rarely rebloom the following season. It’s recommended to treat the bulbs of spent flowers like annuals; pull up the bulbs and discard them.

Overwintering

If growing them in cold-winter zones, garden tulips require no special winter protection. However, withhold watering in fall, as wet winter soil can encourage bulb rot.

Newly planted seeds started in spring in containers need a cold frame to protect them for their first outdoor winter.

Pests and Diseases

Common Pests and Plant Diseases

Tulip bulbs and foliage are popular with many animals, including deer, squirrels, and other rodents. In some areas, it’s not worth planting tulips in the ground; you’re better off growing them in protected containers. Alternatively, you can try deterrents or interplant the tulips with daffodils, but be prepared to lose a few.

Insect pests include:

• Aphids: Wash off with water spray or squash them with your fingers.
• Bulb mites: Sometimes found in purchased bulbs. Inspect the bulbs for signs of decay. A brief two-minute soak in 120-degree water will kill mites.
• Thrips: Combat with sticky traps or introduce ladybugs and green lacewings as predatory insects. Thrip damage may appear as brown or silvery streaks on the leaves of tulips.

Tulips are susceptible to basal rot and fire fungus. Basal rot appears as dark brown spotting or pink or white fungus on the bulbs. Plants that grow from affected bulbs may be deformed or die early. The best remedy is to discard affected bulbs and plant new bulbs that have been treated with a fungicide.

Bulbs affected by fire fungi lead to malformed or stunted plants or plants that never emerge. Affected plants may have curling shoots or dead areas with dark green rings. Treat affected plants with a fungicide. Discard affected bulbs, and plant new bulbs that have been treated with a fungicide.

Common Problems

In the right location and climate, tulips are relatively trouble-free, though hybrid types may decline much faster than you’d like—within three or four years. In addition, there are a few other common complaints:

• Tall Varieties Flop Over

Some hybrid tulips have very large blossoms and flower stalks that can be 2 feet or taller. These types may require staking, especially if the plants are in semi-shady locations, which encourages legginess.

• Plants Collapse at Ground Level

When tulip stems grow soft and collapse at ground level, it’s almost always due to root or stem rot caused by excessively moist soil. Remember that tulips are native to moderately dry regions of Europe and Asia and will do best in conditions that mimic that environment.

• Foliage Is Twisted, Distorted

This is usually a symptom of a severe fungal disease (basal rot or fire fungus) requiring you to dig up and destroy the bulb before it can spread to other plants.

Flowers and Flower Buds Are Streaked, Distorted

This is usually a symptom of tulip virus, for which there is no cure. Affected plants must be removed and discarded—not composted, which can allow the virus to be transmitted.

III. Uses and Benefits

Tulips are among the earlier spring bloomers, so they can be worked into any spot in the yard. They look best when planted in clusters rather than lines. They make good companions for other spring bulbs, like Chionodoxa (Glory of the Snow), late daffodils, dwarf iris, and Scilla.

Cool-season annuals like snapdragons and pansies provide a nice contrast to the cup shape of tulip flowers. The blues of forget-me-nots and Virginia bluebells (Mertensia virginica) play up the bold colors of tulips.