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

September, 2007

 Although summer weather may stick around a little while longer, September signals the start of autumn. The autumnal equinox on the 22nd makes it official. Plants have been adjusting to the shortening days ever since the longest day of the year on the summer solstice in June. Soon, the shorter days will be coupled with cooler nights which is what they are waiting for to begin preparations for winter.

There are two important responses plants have now which we can use to our advantage in better caring for them. Short days and cool nights cause them to begin actively moving starches to their roots for winter storage. Weedy plants such as dandelions and creeping Charlie, treated with broadleaf weedkillers now will move the chemical to the roots, too. That means this is the best time of year to treat broadleaf weeds.

Plants also tend to grow roots more actively in autumn when the air temperatures are cool but the soil temperatures are still warm. That is why you hear the slogan, fall is for planting. Trees and shrubs as well as garden flowers transplanted or dug, divided and moved now have plenty of time to establish their root systems which insures their survival this winter and success next spring.

The 3-digit numbers after a calendar entry can be used to view and print messages on those topics from the UW-Extension's InfoSource website at infosource.uwex.edu. Link to that website and many other sources of information from the UW-Extension's Horticulture team website at wihort.uwex.edu. UW-Extension publications can be printed directly from the publications website at learningstore.uwex.edu.
 

First Week

From August 15th until September 20th is the best time to establish a lawn in Wisconsin either from seed or sod. Both require a good seedbed and even moisture. Step-by-step instructions are given in UWEX publication A3434.
         

If you fertilize your lawn three times a year, it is time for the September application. Wait until the third week or so if you wish to use a combination weed and feed product to control broadleaf weeds at the same time you fertilize. If you are using fertilizer without the weed killer, apply it to dry grass and then water to wash it off the grass blades or apply it just before it rains. If applying a weed and feed product, water thoroughly before or apply it when the grass is already wet from dew or rain. Split the application in half and spread each half over the entire lawn in two different directions to avoid streaking.
    

Leaf lettuce, chard, spinach and radishes can still be planted for harvest yet this fall.

Watch beans for holes in the leaves caused by the second generation of the bean leaf beetle. At first sign of feeding, organic gardeners can use rotenone or neem for control. Others can also use carbaryl or permethrin.

Harvest onions as soon as the tops fall over and begin to dry out. The same applies to garlic. Cure them in warm, dry conditions for a couple of weeks before putting them into cooler, more humid long term storage.

Take cuttings of shade-loving flowering annuals and tender herbs to grow on a sunny window or under lights indoors this winter. Good candidates include wax begonias, impatiens, coleus, lantana, and fuchsia. Geraniums need a lot of light but can survive indoors well enough to be grown outdoors again next year. Parsley, sage, rosemary, basil, oregano, and thyme can be grown indoors, too.


Houseplants that have been "vacationing" in the backyard this summer should be brought in soon. Give them a good blast of water all over before bringing them in to help remove freeloading insects. Insects in the soil are probably not damaging but more of a nuisance when brought indoors. Either be prepared to help them migrate back outdoors for the first couple of weeks after the move or replace the potting soil before bringing plants indoors.

Place amaryllis in storage for a 2 month rest before reflowering. Select a cool (40 - 50 degree) spot and stop all watering. Plan to begin watering again 9 - 12 weeks before you want it to flower.


Thanksgiving and Christmas cactus can be left outside a little longer to expose them to cooler night temperatures. Start letting them dry out more between waterings. This plus the cooler nights will stimulate blossom production.
    

Cyclamen that dried down in spring and were repotted in mid-summer are ready now for more moisture and cooler temperatures to begin flowering.
 

Second Week

A vigorously growing lawn is the best pest preventative strategy. If you have a thatch layer of 1/2" or more, dethatching or core aerating is recommended. When looking at a slice of your lawn in cross-section, thatch looks like a cocoa mat of dead, fibrous material between the green leaves and the soil and roots. Dethatching uses vertical blades to rip out thatch while core aerating makes holes which allow air and moisture to penetrate into the rootzone. Loosened thatch should be raked and removed (or composted) but the plugs of sod and soil brought up by aerating should be left on the lawn. This allows soil microbes to breakdown the thatch layer from the top down. Core aerating has the added advantage of improving heavy clay soils simultaneously. It can also help smooth out bumpy lawns blessed with healthy earthworm populations.
    

Continue controlling leaf diseases on roses. Watch for rose slug sawfly and use a pesticide if the green, slimy worm-like larvae are seen feeding. Plants kept healthy and unstressed by pests are more likely to survive winter conditions. Do not fertilize again this year, however, since late fertilization produces lush growth that cannot mature before the onset of freezing temperatures.
    

Buy colorful, hardy flowering mum plants now for transplanting into beds where dead annual flowers have been or will soon be removed. Some of these hardy garden mums need mounding with soil after the foliage has died. Add two inches of mulch after the ground has frozen to protect them through the winter. Divide large clumps in spring.

 

Third Week

Broadleaf weed killers are even more effective now than in the spring so this is a good time to control dandelions, creeping Charlie, clover, violets, etc. Either spot treat with liquid herbicide formulations or apply weed and feed products.

Fall leaf season is not really upon us yet but it is important to the control of many fungal and bacterial leaf spot diseases that fallen leaves are raked and removed. Leaves from disease-free plants can be managed without collection and removal or burning if you chop them up with the lawn mower. By mowing more often or going over areas with a lot of leaves several times, you can simply "leave 'em be".
    

Radishes can still be planted and harvested this fall.

Many fibrous rooted perennials should be transplanted every 3 - 5 years as a general rule. Fall is the time to divide and transplant plants that flower in the spring while fall flowering ones like chrysanthemums should be done in the spring. Cut back tops to 4 - 6" to reduce transplant stress. Thoroughly prepare the new planting site. Plan to mulch first year transplants well around Thanksgiving to protect even normally hardy species.


Bulbs for spring flowers can be planted through November. Planting early while soil temperatures are still warm promotes good root development. Dig and divide old clumps of daffodils. Replant tulips since one or two years of flowering is usually all they provide. Bulbs should be planted 2 - 3 times as deep as they are wide and one bulb width apart. Good drainage is crucial for most bulbs. Plant individually or in well-prepared beds. Sprinkle bone meal or other high phosphorus material in the planting holes.


Pumpkins, summer squashes, and gourds to be stored should be harvested before the first frost. Pumpkins that have begun showing color will continue to ripen after harvest. Use great care not to nick the rind during harvest since this will lead to more rapid deterioration.
 

Fourth Week

Apple varieties are showing up at fresh markets and roadside stands. Seek out some new varieties to eat fresh or create delicious desserts with. Apple trees can be planted now, too. Select disease resistant ones such as Redfree, Prima, Priscilla, Jonafree, Nova Easygro, and Liberty.

After frost has browned the foliage of non-hardy summer flowering plants such as canna, dahlia, gladiolus, caladium, and tuberous begonia they should be dug and treated for storage. All should be air dried before placing in a cool spot for the winter. Gladiolus are stored dry and uncovered while all others should be covered with well wrung-out peat, soil, or sand to keep them lightly moist.


Fall is a good time to transplant woody landscape plants that are either container grown or balled and burlapped. Dig the hole 4 - 5 times wider than the plant's rootball. Many plants are sensitive to being planted any deeper than they were growing originally so try not to dig the hole any deeper than the ball so that settling does not occur after planting. Use the same soil to backfill without adding organic matter or fertilizer. Mulch the area over the roots and stake trees securely.


Keep harvesting second plantings of the cool season vegetables including radishes, lettuce, Chinese cabbage, chard, spinach, broccoli, and the other cole crops. Some such as parsnips, Brussels sprouts, and kale actually have enhanced flavor after a frost.

Plant individual cloves of garlic now for a crop of garlic bulbs next summer. Select very large cloves to produce the largest bulbs. Plant them 6" deep and at least 6" apart. Mulch them for winter protection after the ground freezes.