Bulbs provide a good investment for money spent and supply years of spring color in your yard. Fall is the prime time for planting of hardy spring flowering bulbs. Most bulbs can be planted until the ground is frozen.
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, peat moss 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).
Both spring and summer bulbs need phosphorous to encourage root development. Keep in mind that phosphorous 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.
If bulbs are going to be maintained in a planting bed more than one year, it is important to supply additional fertilizer. 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 rot and sometimes shortens the life of the flowers.
Summer and fall 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) split over two or three applications over a ten square foot area.
The optimum pH range for bulbs is 6 to 7. A soil test of the planting area is necessary to determine if lime needs to be applied to adjust the soil pH. If needed, limestone should be worked into the soil. For good bud development, work bonemeal into the soil at planting.
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? Since early spring bulbs bloom before most trees or shrubs leaf out, they can successfully be planted under trees and shrubs. Many summer blooming bulbs require full sun or partial shade.
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 the low areas.
The general rule of thumb for planting spring bulbs is to plant two to three times as deep as the bulbs is tall. This means most large bulbs like tulips or daffodils will be planted about 8 inches deep while smaller bulbs will be planted 3-4 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 and loosen the entire bed to the proper depth. Press the bulbs into the soil in the planting area and cover with soil. Because the soil in a spaded bed is better drained and prepared, the planting will last longer. This method of planting is preferred over trying to plant bulbs one by one with a bulb planter. In many soils bulb planters do not work well, if at all.
Water the bulbs 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 bulbs, start watering when the flower buds first appear on the plant if the soil is dry. 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, bloom and early foliage 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 alliums, or the shallow planted bulbs, will rot quickly if over-watered in the heat of summer.
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) that is stored in the bulb for next years 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. Interplant the bulbs in the spring using one or two colors of annuals. Place bulbs behind the plants on the front edge of a border planting. Plant taller flowering bulbs behind lower growing foreground shrubs. Plant bulbs with groundcovers and perennials like hosta or daylilies.
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 or tubers.
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 booming bulbs should not be mulched.
Once the foliage dies back or matures 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 bulbs 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. Some bulbs benefit from digging to divide the bulbs and spread them out over the bed.
If the choice is to dig bulbs, they should be stored in a well ventilated place and replanted in the fall. Every five years daffodils and crocus should be dug and replanted to prevent overcrowding. The first sign of overcrowding will be a decrease in the flower size, uneven bloom and uneven plant height. When this occurs, dig, spread bulbs out and replant immediately.
Most summer flowering bulbs should be dug and stored when the leaves on the plants turn yellow. Use a spading fork to lift the bulbs from the ground. Wash off any soil that clings to the bulbs, except for bulbs that are stored in pots or with the soil around them.
Leave the soil on achimenes, begonia, canna, caladium, dahlia and ismene bulbs. Store these bulbs in clumps on a slightly moistened layer of peat moss or sawdust in a cool place. Wash and separate them just before planting.
Spread the washed bulbs in a shaded place to dry. When dry, store them away from sunlight in a cool, dry basement, cellar, garage or shed at 60° to 65°F. Avoid tempertures below 50° or above 70°F unless different instructions are given for a particular bulbs.
Inspect your bulbs for signs of disease. Keep only large, healthy bulbs that are firm and free of spots. Discard undersized bulbs.
If you have only a few bulbs, you can keep them in paper bags hung by strings from the ceiling or wall. Store large numbers of bulbs on trays with screen bottoms. Separate your bulbs by species or variety before storing them.
Be sure that air can circulate around your stored bulbs. Never store bulbs more than two or three layers deep. Deep piles of bulbs generate heat and decay.
Most flowering bulbs are best stored over a long period 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, sand, perlite or vermiculite. 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.
Source: Ron Cornwell, University of Illlinois Extension Educator