Good Gardening

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University of Illinois Extension
Good Gardening

April/May 2011

Last Edition

Back in October of 2005, I welcomed you all the first edition of Good Gardening. Now, I must tell you that this is the last edition. Due to the reorganization of University of Illinois Extension, my position has been downsized. I will be leaving my position by the end of June.
I have worked for University of Illinois Extension for more than 17 years and I have really enjoyed serving the public through many venues, including this newsletter. Thanks for reading!

Sharon A. Yiesla
Unit Educator, Horticulture
Lake County
Editor of Good Gardening

Crabgrass Prevention

Already the crabgrass preventers are showing up in the stores. But that doesn't mean you should use them yet. Crabgrass seeds will not germinate until the SOIL temperatures are 55-65 degrees for 7-10 consecutive days. For northern Illinois that often does not happen until late April into early May. Even in a warm spring it is unlikely that you will need to use them before the end of April.

When is the Last Frost Date?

This is a common question asked by gardeners eager to plant out annuals and other tender plants. When we talk about the last frost date, we are really talking about the average date of the last frost. Since it is an average, the last frost will occur before that date 50% of the time and after that date 50% of the time. We need to keep this in mind because if we plant our annuals out after the 'last frost date' we may need to watch the weather and be prepared to cover tender plants if cold weather comes our way.

In northern Illinois, Mother's Day is often targeted as the average last frost date and in many years this holds true. In recent years, though, we have had frost as late as the end of May. So go ahead and plant at the appropriate time, but keep your eye on Mother Nature.

A Few "To-Do" Items


  • The first time you mow your grass this season, DO NOT scalp the lawn. This is harmful and opens the lawn to weeds.
  • Late April is a good time to start a new lawn or renovate an old one.


  • In mid to late May we may be able to start planting outside. Watch for late frosts.
  • Thinking about planting a new tree or shrub? This is a good time to do so, since the temperatures are moderating.

Critters to Watch

This is a list of common insects that crop up early in the season and often catch us unaware. Be looking for these pests. If you see them in your yard, call your local Extension office for information on how to control them.


Iris borer: tiny larvae will feed on iris leaves in April and are usually found about the time the leaves are six inches tall. Look for small amounts of damage on the lower part of the leaves. In July, when the larvae are larger, they will move into the rhizome underground and tunnel into it causing more damage.


Eastern Tent Caterpillar: this caterpillar may be seen on trees, usually in late May. They form neat, tidy 'tents' of webbing in the branch angles. The caterpillars come out to feed during the day hours and return to the tent at night. Removing the tent at night gets rid of the problem.

Gypsy moth: the caterpillars are found on trees (often in upper branches) in May. The caterpillar is hairy and has pairs of blue bumps and pairs of red bumps lined up on its back.

Pine Sawfly: The larvae of this pest look like caterpillars and can be found out on the ends of branches on various pine trees. When they are approached, they will pull up their front and back ends in a defensive position. They can easily be knocked off the tree by spraying them with a strong stream of water from the garden hose

Some Shrubs for the Shade

It can be challenging finding shrubs for your shade garden, but there are some good ones out there.
Summersweet Clethra (Clethra alnifolia) grows 4-8 feet tall and has white flowers in late summer. It also has some mild yellow and orange fall color. It tolerates light to medium shade.

Dwarf Fothergilla (Fothergilla gardenii) grows 2-3 feet tall and has white flowers in spring. It will also have good fall color (a mix of orange, red and purple). It tolerates light shade.

Smooth Hydrangea (Hydrangea arborescens) grows 3-5 feet tall has big, round clusters of white flowers in summer. It tolerates full shade.

Oakleaf Hydrangea (Hydrangea quercifolia) grows 3-6 feet tall and has clusters of white flowers in summer. Fall color is russet-red. It tolerates light to medium shade.

Fragrant Sumac (Rhus aromatica) grows 3-8 feet tall. It has shiny green foliage that turns orange to red-purple in fall. Red fruit will be borne on female plants as long as male plants are planted nearby.

May, a Great Month for Gardening

May is often the month to really 'dig in' and get the garden going. Remember, though, that a lot of gardening projects revolve around the last frost date (often mid-May, but some years really more like the end of May). Be watching the weather closely so you don't get caught by frost.

  • Plant perennials (early May, unless a hard freeze comes)
  • Pansies and ornamental cabbage can go out in early May (they are very cold tolerant)
  • Plant annual flowers and vegetables after last frost
  • Dethatch and aerate lawns if needed
  • Apply time release fertilizer to lawns and flower beds if needed
  • Plant summer bulbs after last frost.

Don't Scalp that Lawn!!

Spring is here, let the lawn mowing begin! With the first mowing, it is often a common practice to scalp the lawn (cut it down very close to the ground). This is not necessary and can be damaging to the lawn. Cutting very low puts stress on the lawn by removing too much plant material at one time. It also reduces the amount of shade on the soil and may allow excessive germination of weed seeds, leading to a weedy lawn.

Instead of scalping the lawn on the first mowing, just set the mower height slightly lower than normal. This will remove some of the dead grass and debris without stressing the lawn.

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