Monthly Gardening Calendar
Sharon Morrisey, Consumer Horticulture Agent
Milwaukee County UW-Extension

April, 2008

April transforms our outdoor surroundings from bland to verdant. Green makes a comeback.

Finish the pruning, rake and aerate the lawn, and hope the sun and wind dry out the soil to sow seeds in the vegetable garden.

The average frost free date in southeastern Wisconsin is during the first week of May and later the the remainder of the state. Therefore, you will need to control the urge to plant tender flowers. You should also refrain from clearing away all of the leafy debris from flower gardens. It will serve to protect the emerging, tender shoots from the inevitable frosty episodes yet to come this month. Instead, clean out the shed, sharpen the tools and get the compost pile going again.

The numbers following some of the calendar entries can be used to access InfoSource factsheets from the internet at infosource.uwex.edu.

UWEX publications on these and many other gardening topics can be obtained from the website at learningstore.uwex.edu.
 

First Week

Finish up your pruning chores this month. Pruned branches of spring flowering trees and shrubs like forsythia, pussywillow, apple, crabapple, cherry, plum, and flowering almond can be brought indoors to force into bloom.

Keep Easter lilies well watered. Cut out the bottom of the decorative foil and set the pot onto an inverted saucer or jar lid inside of another saucer to catch the drainage water. As buds continue to open, remove yellow pollen sacs from the stamens before the dusty pollen drops. It not only stains tablecloths and clothes but removal prolongs the flowers.


If you haven't already done so, sow seeds indoors of broccoli, early cabbage, cauliflower, celery, eggplant, and head lettuce. Peppers may be sown from seed indoors now, too.


Alyssum, verbena, calendula, celosia, coleus, dahlia, phlox and salvia can also be started from seed indoors.

Plant a pot of pansies and put them outside. Pansies can tolerate frost, freezing temperatures and even some snow (heaven forbid). If they are greenhouse grown, expose them to the cold a little at a time.

Regularly check rose cones and other heavily mulched or protected plants, such as chrysanthemums. Temperatures can get quite high around these plants on sunny, warm days but it is still cold enough at night to damage new growth. Remove or vent cones only during the day and replace them before the sun goes down.


Open cold frames on sunny days but be sure to close them again before sundown.

Treat pine needle scale on mugo, Scot's, Austrian, white, and red pines with dormant oil. Dormant oil should be used before bud break but when temperatures will be above freezing for at least 8 hours.


Collect soil samples for testing. Sample vegetable gardens, flower gardens, lawns, and shrub beds separately. Each sample should consist of soil taken from 5 different spots within a particular area. Obtain soil sample mailers from your county UW-Extension office.


Begin the process of hardening-off seedlings that will be transplanted outside later this month. This includes broccoli, cauliflower, cabbage, head lettuce, onions, and parsley. At first, place flats in a shaded place protected from the wind. Gradually increase their daily exposure to sun and wind. Bring them indoors each night until just a few days before planting.
 

Second Week

Repair bare spots in the lawn. Work up the soil well in these areas incorporating some granular fertilizer, too. Sprinkle on a good seed mix of bluegrass and fescue. Rake lightly to mix seed with soil. Tamp to assure seed-soil contact. Mulch lightly with straw. Keep well watered for 2 weeks until all the seed has germinated.

Longer days and higher light intensity means indoor plants will begin growing faster. Start fertilizing again using a half strength solution every other watering. Prune hard now to stimulate new, bushier growth.


Prune oak trees before April 15th. Trees pruned later are more likely to contract oak wilt disease from infected beetles feeding on the sap of fresh wounds.

If you have an oak tree that died of oak wilt last season, have it removed and the wood processed (burned, chipped, or at least the bark stripped) before April 15th.


Fertilize grapes, raspberries, and blueberries before growth resumes in the spring. UW-Extension bulletin #A2307 specifies rates.

Cole crops, head lettuce, and parsley may be transplanted outdoors.
 

Third Week

Start tomatoes from seed indoors.

Sow seeds outdoors for the following crops: asparagus, beets, carrots, chard, kohlrabi, leaf lettuce, mustard, onion sets, parsnips, peas, potatoes, radish, spinach, and turnip.

Prepare for apple tree pest control program. If insecticides and fungicides are going to be used, begin treatments as soon as buds begin to expand and grow. A few well-timed sprays early in the season may be all the chemical control necessary. Details are provided in UWEX publications A3565 "Growing Apples In Wisconsin" and A2179 "Apple Pest Management for Home Gardeners".


Begin pest control for peach, plum, apricot and cherry. UWEX publication A2130 provides details.

Establish new plantings of grapes, strawberries, raspberries, asparagus, and rhubarb as soon as the ground can be worked. Proper preparation of the site including pre-plant weed control and the addition of organic matter and fertilizer will assure years of good growth for these perennial crops.
 

 Fourth Week

Raspberry canes that will produce this year's crop should be pruned back by 1/4 before growth resumes. Last year's fruiting canes should have been cut down to the ground after harvest last year. Young canes that will bear this year should have been thinned, too. Leave only 3-5 canes per foot of row or 6-8 per hill.

Check upright junipers and red cedars for the brown galls of cedar-hawthorn/apple rust. They will be mingled with the leaves and resemble brown golf balls. Warm spring rains cause them to ooze orange gelatinous "horns" which spread spores to apple, crabapple, and hawthorn. Remove these galls before they erupt to limit the spread of spores.

Check birch leaves when half expanded for pale circular spots that indicate feeding of birch leaf miner. Early and well-timed chemical control is the key to minimizing the stress caused by this perennial birch pest.


Pre-emergent crabgrass control should be applied by May 1 before this year's seeds germinate. Apply only to those areas where crabgrass was a problem last year.