While easy to grow, tulips do occasionally develop problems. Early emerging foliage, browsing from deer and rabbits, and bulb rot are a few common ones. Below are potential problems encountered when growing tulips in the landscape and how to manage them.
Tulips normally begin emerging from the ground in early April in Iowa. However, mild winter weather can encourage premature growth. The early emergence of bulb foliage is most often seen on the south and west sides of homes and other buildings. These areas are usually warmer than the rest of the yard because sunlight is reflected off the building to the ground. In addition, heated basements keep the soil near homes relatively warm.
While the premature emergence of bulb foliage is undesirable, the danger is not as great as it may seem. The foliage of tulips can tolerate cold temperatures. Often normal winter weather (cold temperatures and snow) returns, delaying further growth. A blanket of snow is especially helpful. The snow discourages additional growth and also protects the foliage from extreme cold.
Tulips are highly desirable to rabbits, deer, chipmunks, voles, mice, gophers, and other animals. These animals can dig and eat newly planted bulbs in the fall and eat the foliage and emerging flower buds right down to the ground in spring. The best way to stop animals from eating spring-blooming bulbs is to exclude them.
To prevent digging, roll hardware cloth or chicken wire across the soil surface after planting and pin it down with landscape staples or bricks. Remove the fencing as soon as the foliage emerges in spring. Once the foliage emerges from the ground, place chicken wire or hardware cloth fencing around the plants. The fencing can usually be removed just as blooming starts to improve the appearance. By that point, the flowers are large enough to not be bothered by rabbits and other animals.
Repellents that rely on strong scents or unpleasant tastes can discourage wildlife pests from coming into an area or browsing on bulbs to prevent further damage. However, repellents are typically not as effective at preventing damage as you would hope. Repellents must be reapplied often, especially after rain events. The label directions will help determine the frequency of necessary applications. Treat those areas that have been affected as well as areas nearby to prevent further damage. While repellents may not be very effective on their own, they can be used with other management options to further help prevent damage.
If tulip bulbs are not planted before winter, they often shrivel up and die over winter. Tulip bulbs that remain viable (alive) over winter usually don’t perform well when planted in spring. Spring-flowering bulbs are planted in fall so the bulbs have adequate time to develop good root systems before winter. Additionally, they must be exposed to cold temperatures to bloom. Bulbs planted in the spring usually don’t grow well because they lack well-developed root systems. Plus, they often fail to bloom. Regrettably, it’s usually best to discard unplanted tulip bulbs in spring. Buy and plant additional bulbs in the fall.
Most modern tulip cultivars bloom well for three to five years. Tulip bulbs decline in vigor rather quickly. Weak bulbs produce large, floppy leaves but no flowers.
To maximize the number of years tulips bloom, choose planting sites that receive at least six hours of direct sun per day and have well-drained soils. Promptly remove spent flowers after the tulips are done blooming. Seedpod formation deprives the bulbs of much of the food manufactured by the plant’s foliage. Lastly, allow the tulip foliage to die back naturally before removing it. Tulips that don’t store adequate amounts of food in their bulbs cannot flower.
Dig up tulips that are no longer blooming and discard the bulbs. (Small, weak tulip bulbs will likely never bloom again.) Plant new tulip bulbs in the fall.
While most modern tulip cultivars bloom well for three to five years, some tulip types (classes) bloom well over a longer period. Darwin hybrid tulips are generally the longest-blooming hybrid tulip. Fosteriana tulips (also known as Emperor tulips) also bloom well for many years.
The foliage of tulips can tolerate cold temperatures well. Occasionally some damage may be seen when freezing temperatures hit spring bulbs later in the spring season while they are fully emerged and in bud or bloom. Overall even flowers can tolerate light freezes (low 30s to upper 20s °F) and even a little snow. Record cold temperatures (below the mid to upper 20s) will damage or destroy many of the flowers of early blooming varieties. The foliage of fully emerged tulip blooms can also be damaged. Portions of the leaves may turn white and the damaged leaves may collapse onto the ground.
No immediate action is needed to preserve cold-damaged spring bulbs. Despite its poor appearance, the foliage should not be cut back until it turns completely brown. The undamaged portions of the leaves need to be able to manufacture as much food as possible to have blooms next spring. If foliage is damaged but flower buds are not impacted, plants may still bloom.
Tulips that develop stunted, yellowed leaves or fail to emerge in the spring may be suffering from bulb rot. Cool, soggy conditions can favor infection by certain soilborne plant pathogens. Several different fungi and bacteria may infect bulb tissue.
These microorganisms often gain entrance through wounds created by insects or improper handling of the bulbs. Extended periods of wet weather favor infection. Diagnosis of below-ground problems involves hands-on investigation. Symptomatic plants need to be dug and examined. Diseased bulbs usually are discolored, soft, and may emit a foul odor. In some cases, there may be a black or bluish mold on the bulbs.
Diseased bulbs should be discarded, along with some of the surrounding soil. The best way to prevent the occurrence of bulb rots is to make sure the planting site is well-drained. Avoid planting in areas that are poorly drained or that collect water.
To minimize convenient entry points for pathogens, avoid wounding when handling bulbs. Buy from a reputable source and examine bulbs for bruises or other damage. Plant at the proper depth, encourage good air circulation, and manage water needs. Plants that are growing vigorously are best able to resist diseases.
Botrytis blight, also called tulip fire, is the most common tulip disease. Damp, overcast weather favors the growth of the causal fungus, Botrytis tulipae. This fungus commonly attacks tulips that have been damaged by frost or hail.
All parts of the plant may be infected. Leaves show small, slightly sunken oval spots that usually have a dark margin. These spots may enlarge and coalesce with moist conditions, sometimes involving entire leaves. Stems may rot off completely. Flower lesions also appear as small oval spots that are light in color. The entire flower may eventually become blighted. The outer scales of the bulb develop blackish fungal structures called sclerotia. These resistant structures allow the fungus to survive the winter and remain viable in the soil for years.
Botrytis, also called gray mold fungus, can be seen on diseased plant parts in moist weather. Under these conditions, the fungus produces large numbers of spores, causing a grayish mold to appear. These spores are spread to neighboring tulips by air currents. Plants that grow from diseased bulbs are a common source of infection.
Certain cultural practices can help control Botrytis blight. Examine bulbs before planting and discard any that appear damaged or moldy. Because the infection is more likely to occur on bulbs that have been bruised or cut, take care to prevent injury to bulbs. Diseased plant parts should be removed as soon as symptoms are noticed. Working around plants during dry conditions will help reduce the risk of spreading the disease. If desired, protection from disease can be achieved by applying a fungicide starting when the leaves emerge from the soil and spraying several times until the bloom stage. Because the tough sclerotia produced by the fungus can survive for several years in the soil, it is best to rotate the planting site for tulips.