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Planting spring bulbs before winter

Published September 21, 2010
If your spring landscape needs a little brightening, fall is the time to plant some bulbs, said a University of Illinois Extension horticulture educator.

"With a proper selection of bulbs and bulb-like plants, you can have very reliable blooms from February until November, but spring is when bulbs shine the most," Jeff Rugg said.

True bulbs, like daffodil, lily, tulip and onion are composed of modified leaves. Cutting a true bulb in half vertically will reveal an en¬tire miniature plant. Next year's leaves, roots, stem and flowers are surrounded by the leaves of the bulb, which stores all of the food necessary for growth.

A corm is modified stem tissue that is used to store food. Crocus, gladiolus, and freesias all grow from corms. The top of the corm has tiny growing points called eyes that develop into leaves, stems, and flowers.

A tuber is another type of underground stem used for food storage. Anemone, gloriosa lily, ranunculus, and potato grow from tubers. Tubers also have eyes that grow into all of the adult plant's parts.

Most spring bulbs prefer morning sun and afternoon shade. Plant daffodils and crocuses in light tree shade. While grape hyacinths prosper in heavy shade, most bulbs will not be able to store enough food to flower well in such conditions. In these cases, you may need to replant every few years for the best blooms.

"Good drainage is a must—the bulbs will rot and be unable to bloom if the ground stays soggy," Rugg added.

Large beds of solid colors or companion plantings of bulbs, perennials, and evergreen ground covers look much better than planting a few stragglers. When buying bulbs, plan to plant them in groups of about 30.

Small bulbs, such as crocus or trout lily, naturalize well in the lawn as long as you wait to mow until the foliage turns brown. The bulbs can then store enough energy to grow another year.

"Unfortunately, most people will mow the lawn before the bulbs are able to store enough energy for the following year," Rugg said.

Most bulbs are best planted two to three times deeper than the size of the bulb. Large bulbs should be planted about eight inches deep and small ones three to five inches deep. The pointed end of the bulb should face upwards. Space large bulbs six inches apart and small bulbs three inches apart.

Multiple bulbs can be planted into the same hole. Plant the lower bulbs first and add a thin layer of soil before planting smaller bulbs over the top.

"Try not to plant the upper layer of bulbs directly over the lower bulbs," Rugg said. "Plant them so they will grow between each other. Do not plant too many bulbs in the same hole or they will become too crowded when they begin to grow.

Before planting, the soil should be amended with bone meal or bulb fertilizer and loosened about three inches below the bulb planting depth so the roots can grow into good loose soil. Cover the bed with three inches of mulch or compost and water thoroughly. Keep the bed moist until the ground freezes. If it is a dry or warm winter, more watering may be required.

In parts of the United States that do not get three full months of freezing weather, the bulbs will not be able to break through their dormancy. Some southern nurseries store bulbs in a refrigerator for three months to meet their cold dormancy needs. These bulbs will bloom early and should be treated as annuals because they will not bloom again if left in the ground.

"You will want to plant the bulbs as early as you can in the fall, so they have the most time to grow roots before the ground freezes," he said. "However, they should not be planted until after the ground cools to about 60 degrees Fahrenheit. This usually occurs after the first killing frost, so use that date as a reminder to plant them soon after that.

"If you forget to plant the bulbs at the right time, you can still plant them even if the ground is frozen. The bulbs will not put out roots in the fall like they should, but they will still get their cold dormancy period."

You can also place the forgotten bulbs in flower pots filled with potting soil. Cover the bulbs to just over the top of the bulb and put the pot in a plastic bag. Then place the pot in the refrigerator. When the bulbs begin to sprout, take off the plastic bag, but do not forget to keep the soil damp.

"Refrigerators dry out the soil quickly, so keep an eye on the pot," Rugg said. "After three months in the refrigerator, bring the plants out to a sunny windowsill to grow. They can be planted in the ground as soon as the weather warms up, but if they do not get a full season of leaf growth, they probably won't bloom for a year or two.

"Potted spring bulbs can be planted in the ground and, after three months of cold weather, be brought indoors where they will bloom."