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Month-by-Month Gardening Guide: September

Groundcovers and Lawns:

After a tough summer, what do you need to do to revive that sun-scorched turf? First, take a look at your fertilization schedule.  Remember that cool-season lawns need fertilizer when temperatures are cooler (i.e. spring and fall).  In fact, if you can only fertilize once a year – do it in the fall. As turf is recovering from the semi-dormant state of summer it will need that boost to prepare for winter.  Mark your calendars for September 1, October 15, and November 15 and on each of these days apply one pound of nitrogen per 1,000 sq. ft. Base your phosphorous and potassium applications on a soil test for best accuracy. Lime should never be applied without first knowing the recommend amount based on a soil test.  By the way, fall is great time to soil test in Tennessee since the University Soil Lab is less crowded and can often return results in less than two weeks. Considering renting a dethatcher (power rake) and core aerifier to help remove thatch build-up and loosen hard soils.  Doing this process before fertilizing will ensure nutrients reach the grass roots.

If you are growing warm-season grasses such as Bermuda and Zoysia, it’s time to prepare them for winter.  Raise your mowing height and allow grass to ‘winter-through’ taller than your preferred mowing level since taller blades will help buffer the plant from cold damage. Applying a potassium fertilizer on September 1 will also increase warm-season grass cold hardiness. Many of these fertilizers are sold with pre-emergence herbicide that will prevent the germination of winter weeds, alleviating some problems next spring.

Perennial Flowers and Vines:

Ornamental Grasses add texture, contrast, color and year-round interest to the landscape and the beauty of these plants in perennial borders or as mass plantings certainly deserves recognition. There is a large variety of grasses available for Tennessee landscapes and their uses are just as varied.  Shorter grasses are useful for edging, mid-sized grasses add vertical lines and blend textures and taller grasses provide structure or backbone to flower beds. The following are some recommended varieties for various situations:

  • Grasses for screening: Big Bluestem, Indian Grass
  • Grasses for use as groundcovers: River Oats, Creeping Red Fescue
  • Grasses with red foliage: Red Switch Grass ‘Rubrum’
  • Grasses for dry sites: Little Bluestem, Love Grass

Be aware that some grasses can become invasive.  Some ornamental grasses like River Cane, Ribbon Grass and particularly Japanese Blood Grass are considered exotic plant pests and considered highly invasive.  This part of the article has been edited because the original article included grasses that are invasive and some deemed “noxious weeds” by Tennessee.  Native grasses have been used to replace the original and invasive exotic pest plants.

Trees and Shrubs:

In late summer or early fall when hot temperatures fade, cool season mites like the spruce spider mite again become active.  The mites remain dormant during the summer in a round, reddish-orange egg stage. With the advent of cooler weather, the eggs hatch and the mites feed on evergreen plants such as arborvitae, juniper, spruce, hemlock, false cypress, and Leyland cypress.  Populations can build to damaging levels during the fall.  Some of the last eggs laid in the fall will remain dormant and hatch during warm spring days in April.  Many people blame the harsh winter weather for the bronzed foliage on evergreen plants in the spring.  Many times this discoloration is due to spruce spider mite feeding damage from the previous fall.  Check plants for active spruce spider mites in both the spring and late summer-early fall.  Hold a tablet of white paper directly beneath a branch and strike the branch solidly three times with your hand or a broom handle.  Any active mites will be knocked onto the paper and soon start crawling.  They are about the size of the period at the end of this sentence.  Run your hand across the paper and the smashed spruce spider mites will make olive-green streaks.  Other mites may be dislodged from the plant however many are beneficial and feed on fungus or other mites. These mites do not leave streaks when smashed. Chemical control using horticultural summer oil, insecticidal soap or miticides is best achieved when the first flush of mites have hatched from their eggs.  A follow-up spray is needed about a week later.  A dormant oil spray can be made in late February-early March to kill many of the overwintering eggs.  A dormant oil spray works best when the temperature is 50 F or higher.

Fall is a great time to plant trees and shrubs in your landscape. To ensure success during this planting season, follow these six simple guidelines:

  1. Plan.  Have you ever been at a nursery and purchased a plant, brought it home and then asked “Where should I plant this?” Now be honest, remember the small holly that now blocks your rear windows or the sweet-smelling mint that escaped the flowerbed and attacked the front lawn? Most gardeners have been guilty of this process at least once in their garden’s life. Successful gardens require planning. Study your lawn to learn how much sun you receive, how well the soil drains, where the underground utilities and power lines run and take a soil sample to determine the pH and fertility of your soil. Ask yourself if your landscape is appropriate for a specific tree.
  2. Select. Yes, it is cheaper to buy plants that are on the clearance rack but there are dangers in this miser-mentality. Spindly or yellowed plants may be a sign of problems, such as root-rot, a disease that can spread to your other plants, given the right conditions. Select plants that have vigorous growth and good leaf color. Inspect the roots to be sure they are white and firm. You will have more success from a healthy plant.
  3. Handle with Care. Transporting trees and shrubs home can be hazardous. Take care not to damage the trunk or break limbs.  Dropping heavy rootballs can also break tender roots.
  4. Dig a Proper Hole. A common mistake made when planting trees is digging the hole too deep. Dig your hole as deep as the rootball is high so that when the tree is placed in the hole it is at the original depth that it grew in the nursery. The hole should be two to three times the width of the rootball and sloped inward to allow young roots easier access to surrounding soil.
  5. Plant. This is another step where people often make mistakes. The rules you need to remember are simple.  First, consider the method by which the plant was sold and prepare the roots accordingly: for bare-root plants, spread out the roots before backfilling the hole; for container plants, remove the container and cut and spread out any girdling roots; for balled and burlapped plants, set the tree in the hole and cut away any strings and burlap from the top and sides of the ball, leaving the bottom intact, if a wire basket was used, remove as much as possible without damaging the rootball. Use the existing soil to backfill the planting hole, do not amend this soil since problems can occur with water retention and root growth. Apply a two to three inch layer of mulch around the tree keeping the mulch at least six inches from the trunk to prevent disease and rodent problems.
  6. Water, water, water. Even if a person follows every step completely, many lose trees and more often than not the problem can be traced back to water.  A newly planted tree must have water to survive. The recommendation is at least an inch of water per week, and is best if supplied slowly through irrigation or soaker hoses which will allow it to infiltrate the soil and soak the surrounding ground.

Vegetables and Herbs:

It’s near the end of the growing season for many of our vegetables and perhaps you still have produce in the field. What’s the best way to store those vegetables for use later? Consider these guidelines:

  • Vegetables like swiss chard, collards, green onions, lettuce, greens, and spinach should be kept at 32 to 41°F and 85 to 95 percent relative humidity. Try the refrigerator crisper but keep the crisper more than half full to maintain the humidity. Wash and drain the vegetables before storage.
  • Asparagus, beets, broccoli, carrots, cauliflower, peas, and rhubarb can also be stored in crisper when in plastic bags but should be kept separate from the vegetables above.  These will also keep in containers in the main compartment of the refrigerator.
  • Peppers, cucumbers, melons, snapbeans and summer squash will keep best at 45 to 55°F and 85 to 95 percent relative humidity. These conditions are hard to reproduce in the home so you should only plan to leave these in a refrigerator for about seven days and use immediately.
  • Eggplant, okra, ripe tomatoes, winter squash, Irish potatoes (keep in subdued light), and sweet potatoes can be injured by cold temperatures and should be stored in a cool place, 50 to 60°F, such as a pantry, basement or garage.
  • Dry garlic, dry onions, and mature green tomatoes can be stored at room temperature, 65 to 70°F, and out of direct sunlight.

As you can see, different vegetables require different storage methods. In all cases, you should begin with only the insect and disease free vegetables.  Check your vegetables often for spoilage and remove those showing symptoms before rots spread.

Around the Home:

To avoid problems with ladybeetles, boxelder bugs, and spiders invading your home this winter – do some pest-proofing today.  Many of you may have experienced lady beetle invasions in the past.  The majority of problems with this otherwise beneficial insect are expected later this month.  One of the best ways to prevent unwanted invasions by insects (also rodents, birds, etc.) in the home is to deny entry.  The following tips will give suggestions that not only block insects from seeking shelter in homes, but also conserve energy and increase the comfort level during summer and winter.

  1. Install door sweeps at the base of all exterior entry doors.  One way to check the seal around your door is turn on all the lights in the house at night and take a walk around the outside of the house.  If you see gaps of light around the seal of 1/16 inch or more from outside the house, there is a possibility for entry of insects and spiders.
  2. Seal utility openings where pipes and wires enter the foundation and siding (i.e. outdoor faucets, gas meters, clothes dryer vents). Holes can be plugged with caulking, cement, steel wool or urethane expandable foam.
  3. Use a quality silicone or latex caulk around windows, doors, etc. Prior to sealing, cracks should be cleaned and any peeling caulk removed for adhesion.
  4. Repair gaps and tears in window and door screens to help reduce entry of flies or gnats in summer or cluster flies and lady beetles in early fall.
  5. Install 1/4 inch wire mesh (hardware cloth) over attic, roof, and crawl-space vents in order to prevent entry of squirrels, birds and other wildlife.

Since ladybeetles are such beneficial insects in our gardens, many people hate to destroy those that are overwintering indoors. If this describes you, why not make them feel at home.  Obviously, you can’t let them fly freely in your home but you can provide them an overwintering site. Collect the ladybeetles and place them in a jar with a piece of cardboard and air holes in the lid. Place this jar in your refrigerator and once per week sprinkle water into the jar. Allow the jar to set out for at least 30 minutes (keep out of full sunlight) while the beetles become active and drink the water, then return the jar to the refrigerator. When temperatures remain above 55°F in the spring, release the ladybeetles back into your garden where aphid populations have already begun.

Updated August 30, 2010

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