Bulbs can be classified as spring flowering bulbs or summer flowering bulbs. Another way to classify bulbs for use in Illinois would be hardy spring flowering bulbs and tender summer flowering bulbs.

Summer flowering bulbs (tender bulbs) are bulbs that are killed by cold temperatures. They must be planted in the spring when there is no longer a chance of ground frost. They need to be dug in the fall following the first frost that discolors the foliage and stored over the winter.

The spring flowering bulbs (hardy bulbs) such as tulips, daffodils and crocus need a cold period during the winter to flower. These bulbs are planted and develop a root system in the fall and bloom during the spring. Temperatures are cold enough in Illinois during the winter to meet these cooling requirements. For instance, tulips require 12 or more weeks of cold temperatures. If spring bulbs are used for forcing indoors, be sure they have been pre-cooled or they will not bloom.

BLOOMING SEASON

By raising both spring flowering and summer flowering bulbs, the blooming season can be extended. Spring flowering bulbs normally start blooming in February with snowdrops and end in June with the alliums. The summer bulbs extend the bloom period from July into the fall season.

OBTAINING BULBS

It is important to select good quality bulbs for planting. Factors to consider are size and firmness. Larger bulbs produce larger blooms. Select bulbs that are firm and free from soft or rotting spots or other signs of disease.

There are basically three sources for obtaining bulbs: mail order businesses, local nurseries and discount businesses. Normally, there is a larger selection of bulb varieties through mail order catalogs. The disadvantage of mail order is that the buyer does not know what the bulb will look like until received. Therefore, always buy from companies that have good reputations and that you or your friends have used in the past with good results.

Once bulbs are obtained, either locally or from a mail order source, they should be planted as soon as possible. If the bulbs cannot be planted immediately, keep the bulbs cool until they are planted. The preplanting storage temperature should be between 50°F and 60°F. Keep the bulbs away from ripening fruits which may produce ethylene and cause flowering disorders, especially with tulips.

PREPARING SOIL

Properly preparing the soil for bulb planting is important. Good soil drainage is essential in raising bulbs. If you have a soil with a high clay content, it can be improved by adding compost or some other source of organic material. The organic material should be worked in the top twelve inches of soil (eighteen inches is even better).

FERTILIZATION

Both spring and summer bulbs need phosphorus to encourage root development. Keep in mind that phosphorus moves very little once applied to the soil. Some bulbs are planted 6 to 8 inches deep. The phosphorus needs to be mixed in the soil below where the bulbs will be located so it can be utilized by the bulb roots. Mix bonemeal or superphosphate with the soil in the lower part of the planting bed as it is being prepared.

Spring flowering bulbs should have mixed into the soil in the fall five tablespoons of 10-10-10 soluble fertilizer (or equivalent bulb fertilizer) plus two cups of bonemeal per ten square foot area. As soon as the shoots break through the ground in the spring, repeat the above soluble fertilizer application. Do not fertilize spring flowering bulbs after they have started flowering. This tends to encourage the development of bulb rots and sometimes shortens the life of the flowers.

Summer flowering bulbs should be fertilized monthly from shoot emergence until the plants reach full flower. Apply seven tablespoons of 10-10-10 soluble fertilizer (or equivalent bulb fertilizer) per ten square foot area.

The optimal pH range for bulbs is 6 to 7. A soil test of the planting area is necessary to determine if limestone needs to be applied to adjust the soil pH. Limestone should be worked into the soil.

PLANTING LOCATION

Before selecting the location to plant bulbs in the landscape, consider the light requirements of the plant. Does the plant require full sunshine, partial shade or full shade? Early spring blooming bulbs can be planted successfully under deciduous trees or shrubs. They should not be planted under evergreen trees or shrubs that block the sunlight. Spring bulbs planted on a south slope will bloom earlier than the same bulbs planted on a north slope. Spring bulbs planted on a hillside will bloom earlier than bulbs planted in a valley. Cold air is heavier than warm air and behaves like water. It flows down the slope, settling in low areas.

PLANTING DEPTH

The general rule of thumb for planting spring bulbs is to plant two to three times as deep as the bulb is tall. This means most large bulbs like tulips or daffodils will be planted 6 to 8 inches deep, while smaller bulbs will be planted about 4 inches deep. Planting depth is measured from the bottom of the bulb. This rule of thumb on planting depth does not apply to summer bulbs which have varied planting requirements. For planting depth of summer bulbs, consult the information supplied with the bulbs.

Tulips, daffodils and hyacinths should be planted with the nose of the bulb upward and the root plate downward. The best method of planting is to dig out an entire bed or trench to the proper depth. Press the bulbs into the soil in the planting area and cover with soil. In establishing a naturalized planting, the bulbs may be planted one by one using a bulb planter or auger.

WATERING BULBS

Bulbs should be watered following planting. This will help settle the soil in the planting bed plus provide needed moisture for the bulbs to start rooting. Fall planted bulbs must root before cold weather. Avoid over-watering at planting time since this can result in bulb rot.

For both spring and summer blooming bulbs, start watering when the flower buds first appear on the plant. Shallow watering will not do the job. Remember that the bulbs may have been planted 6 to 8 inches deep and the water needs to soak to that depth. Through the bud and bloom stage, add about one inch of water per week if this amount has not been supplied from rainfall. Water with a soaker hose to keep water off the bloom. Bulbs like the alliums or shallow planted bulbs will rot quickly if over watered in the heat of summer.

MOWING FOLIAGE

One of the visual problems with spring bulbs is the foliage that remains after bloom. The foliage can become unsightly if the bulbs are planted in a public area of the landscape. Foliage should not be mowed off until it turns yellow and dies back naturally.

The foliage on the smaller bulbs such as snowdrops and squill will die back rapidly and cause little problem. The foliage on the larger bulbs like tulips and daffodils will take several weeks to die back. Keep in mind that after flowering, the plant needs the green leaves to manufacture food (photosynthesis) which is stored in the bulb for next year's growth. If the homeowner mows off the foliage early, the plant can no longer manufacture nutrient reserves for next year. This results in a small, weak bulb which will gradually decline and die out.

There are several ways to divert attention from the yellowing bulb foliage. Place bulbs behind the plants on the front edge of a border planting. Plant taller flowering bulbs behind lower growing foreground shrubs. Planting bulbs with groundcovers and perennials like hosta or daylilies will help camouflage the foliage. Interplanting a bulb bed with annuals is not very effective because of slow annual growth in the spring.

MULCHING

The bulb bed should be covered with two or three inches of mulch. Mulch will help minimize temperature fluctuation and maintain an optimal moisture level in the planting bed. The small, early blooming bulbs should not be mulched.

STAKING

Some of the summer blooming bulbs like dahlias and gladioli occasionally need extra support to be able to remain erect. A support ring is an easy way to support plants that have weak stems. Stakes will also work for this purpose. Drive stakes in place at planting time to avoid accidental damage to the bulbs.

DIGGING BULBS

Once the foliage matures and dies back in the late spring or early summer, the bulb is dormant. Summer is the dormant period for spring bulbs. As the foliage dies back, the roots that nourish the bulb also die back. With fall rains, the bulb comes out of summer dormancy and roots begin to grow again to provide the bulb nutrients and moisture.

Once the spring bulbs enter dormancy, the time is right to dig the bulbs if needed. If the flowering of the bulbs was satisfactory, do not disturb them.

Every five years daffodils and crocus should be dug and replanted. The first sign of overcrowding will be a decrease in flower size, uneven bloom and uneven plant height. When this occurs, dig, spread bulbs out, and replant immediately.

STORAGE

The bulbs that require storage over a period of time are the summer blooming bulbs that must be dug in the fall to prevent freezing. Spring flowering bulbs may require storage for a short period of time after purchase if weather conditions are such that they cannot be planted immediately.

Bulbs that need to be stored over a long period of time should be kept at temperatures between 60°F and 68°F. Try to keep the humidity in the storage area as low as possible. Never store bulbs in an area where ethylene gas produced by fruit is present. Bulbs can be stored in a container with peat moss, perlite, vermiculite or shredded paper. Another common storage method is to place the bulbs in a very loose knit sack and hang in a sheltered, cool area. Do not divide or separate bulbs before storing them.