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Bulbs add color, form and fragrance to Midwest gardens
Chicago Botanic Garden
By Tim Johnson | Guest Columnist

Crocuses can be planted in rock gardens, under trees or directly in the lawn. Above is an autum crocus, so named because it blooms in the fall.


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Published: 10/2/2010 12:01 AM

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Hardy bulbs deserve more use in Midwest gardens. They add versatility in color, flower form and fragrance and can provide extended seasonal interest with proper bulb selection.

General garden care

Buckthorn is an invasive tree and common throughout the Chicago area. Late in fall it tends to hold green leaves later than other deciduous trees so it is easy to spot. Cut at ground level and quickly treat the stump with an herbicide to kill the root system.

Shredded leaves make good mulch for your garden beds. For the serious gardener, a shredder can be rented but note that they are very noisy so ear protection is a good idea. Using a shredder is a time-consuming process but results in finer leaf mulch. For the average gardener, a lawn mower with a bag to catch the leaves works fine for this job. The mower doesn't cut the leaves up as finely as a shredder but works a lot faster. Ground-up leaves will also decompose more quickly if you are using them in a compost pile.

After a killing frost, remove dead plant debris from annual and vegetable beds. Sanitation is especially important if you have had disease problems in your planting beds. Remove all diseased foliage or fruits and do not add affected materials to your compost pile, as most home compost piles do not get hot enough to kill disease organisms.

In general, it is not necessary to mulch established perennial borders. Leave perennials up for winter interest and leave a light layer of leaves in the bed to provide some winter protection. Cut back perennials when they start looking bad. Any perennials planted this year should be mulched for the winter. The freeze-and-thaw cycle in spring can push newly planted perennials out of the ground.

Terra cotta containers need to be stored out of the elements for winter. When plants in these containers are finished for the year, dump out the growing medium and store the pots in a garage or shed so they are out of the rain. These containers absorb water and the freeze-and-thaw cycles of winter can crack them if they are left outside.

The average first frost at the Chicago Botanic Garden is Oct. 15, though it is often later in the city. Tender plants can be protected from light freezes by covering them with sheets, plastic or boxes. When night temperatures begin dropping below 40 degrees, it is time to bring in any tropical plants you are keeping outside.

Warm fall days are great for installing Christmas lights. Wrap branches of your trees with strings of lights to accent the tree's form. Chicago Botanic Garden staff starts installing thousands of twinkling lights in mid-October.

It is best to avoid using crushed limestone for the base of hardscape features such as walks and patios. Limestone increases the alkalinity of soils and will make growing some plants more difficult if they are adjacent to the limestone base. Grade 9 gravel with fines works well for the base of patios and walks because it easily compacts.


Order bulbs early to ensure getting the varieties you want. When buying in a garden center, pick bulbs that are plump and firm with no mushy spots. Small nicks, loose tunics or blue/gray mold do not affect the development of bulbs. Bulbs with white mold or that are soft and lightweight with a strong moldy smell are probably not good. If your bulbs cannot be planted right away, store them in a well-ventilated area that is cool but above freezing, out of reach of rodents and away from ethylene-producing materials such as ripening fruit. Artificial heat will dry bulbs, while high temperatures may destroy next spring's flower in the bulb.

Most bulbs should be planted after a hard frost starting mid-to late October and before the ground freezes. Fall-flowering bulbs such as autumn crocus (Colchicum) should be planted as soon as they arrive in early to mid-September. Bulbs rarely look good alone or in rows. Plant them in clumps or drifts. Bulbs such as daffodils and squill can be naturalized or planted to look as if they are growing wild. One way to do this is to toss handfuls of bulbs and plant them where they land. Small bulbs such as crocus should be planted in large groups of at least 30 to 50 so they are prominent in the landscape. Incorporate bulbs into the perennial border in groups of seven to 15 bulbs or more.

If you are planting bulbs for next spring, keep in mind that daffodils are one of the hardiest, most adaptable and pest-resistant bulbs for Chicago-area gardeners. They naturalize beautifully and are available in many sizes and bloom times. Proper selection of varieties will give three to five weeks of constant bloom. Deer, squirrels, chipmunks and rabbits do not eat them. Ornamental onions also will not be eaten by animals. Tulips are a deer and rabbit favorite. In my garden, squirrels and chipmunks have left winter aconite and snowdrops alone while devouring all my crocus.

Proper placement is important for success with spring-flowering bulbs. They prefer moisture in early spring and fall and to be dry in the summer when they are dormant. They do not like wet sites or heavy clay soil. If soils are on the heavy side plant bulbs higher than normally recommended. In general, plant bulbs at three times the diameter of the bulb.

Crocuses are ideal bulbs for naturalizing, for rock gardens or for under-planting beneath tall trees. They may be scattered in lawns, but their grass-like foliage must remain intact at least six weeks before being mowed with the grass. Crocuses, which are planted shallowly, are easy targets for rabbits and squirrels and might require repellant products or light chicken wire screen placed directly over them at planting time. Blood meal sprinkled on the ground after planting may help repel squirrels and chipmunks.

Certain bulbs such as daffodils, hyacinths, tulips and crocuses are excellent for forcing in pots in the greenhouse or home. They need to be chilled for six to 10 weeks at 40 degrees or below to fulfill the requirements of a dormant period. Plant them in pots in the fall and leave in a cold place in the fall before bringing inside for forcing. Place the pots in a cold frame outside, plunging the pots into the ground and mulch. Do not allow the pots to dry out. When they are brought inside, acclimate them gradually to inside conditions, keeping them at 50 to 60 degrees for a few days.


Continue cutting your grass throughout the fall as needed, taking care to stay off the lawn when there is heavy frost present. Cold weather will eventually stop grass growth. Make your last cut of the year at a lower height of 2 inches.

Schedule a time to have your sprinkler system drained for winter. Water left in the system can freeze and crack sprinkler heads and pipes. Compressed air often is used to blow water out of the system.

•Tim Johnson is director of horticulture at Chicago Botanic Garden.