Tend to critical gardening tasks in September

Early September is a watershed time of the gardening year. Summer is essentially over, and fall is just around the corner. There’s a two-week window for critical gardening tasks. Let’s outline some of the more critical ones:

Pre-emergent weed-killer treatment. You get one chance per year to prevent the germination of cool-season weeds. If you even wait until the middle of September, the window may have closed. Once weed seeds sprout and start growing, pre-emergents will be ineffective. Several types such as Team and Dimension are specific for weedy grasses, such as annual bluegrass (Poa annua), fescue grass and ryegrass. Gallery products work on nongrassy (broad-leafed) weeds such as clover, dandelions, henbit and chickweed.

Mow your lawn, then apply one of these granular products, and finish by watering the lawn lightly. This will leave a layer of the herbicide across the surface of the soil. Pre-emergent weed killers stop the seedlings just as they germinate.

Fall feedings. Horticulturists and turf authorities say that your fall fertilization is the most critical feeding of the year. If you have a heavy clay soil, it has undoubtedly accumulated excessive amounts of phosphorus, the middle number of the analysis, so applying an all-nitrogen product is advised. Use a high-nitrogen fertilizer for sandy soils. Apply the plant food to your entire lawn and all of your landscape and garden plants, then water heavily to soak it into the soil. If you’re going to be applying a pre-emergent weed killer as well as a fertilizer, spread the plant food first, followed by the heavy watering. Wait a day or two, then apply the pre-emergent, and water again lightly.

Application of iron/sulfur products. By late summer, many of our landscape plants have begun to show severe iron deficiency. Chief among them are azaleas, gardenias, hollies, ligustrums, Carolina jessamine, cherry laurels, pines, dogwoods and wisteria. Iron becomes insoluble in alkaline soils, so plant roots are unable to take it in. The deficiency shows up as yellowing leaves with dark green veins — most prominent on the newest growth at the ends of the branches.

Treatments to correct iron deficiency chlorosis must be made from late spring into early fall. You’ll find many iron-based supplements in garden departments. The better ones also will have sulfur. It’s not that plants need sulfur, but iron-requiring types benefit from sulfur’s acidifying effects on the soil. By lowering the soil’s pH, sulfur helps to keep some part of the iron in a soluble form. Be careful, however, not to let iron products come into contract with bricks, concrete, pavers or painted surfaces. They can leave permanent, rust-colored stains.

Root-pruning landscape plants. There are two specific reasons for doing this. If you intend to move an established tree or shrub during the winter dormant period, root-pruning it now will give it time to regrow roots in the soil ball. Second, if you have a wisteria that has been shy to bloom the past several years, root-pruning often will shock it enough that it will set flower buds in the fall. Cut a slit 12 to 15 inches deep around any plant you’re trying to root-prune. The cut should be made at roughly the same spot where the final cut will be made in the winter. For wisterias, it should be 15 to 18 inches out from the trunk.

Planting new grass. Winter becomes your nemesis when it comes to starting warm-season grasses in the fall. You have to allow enough time for the turf to develop strong, deep roots, and for North Texas, the cutoff time is mid-September for St. Augustine and zoysia sod and Bermuda seed. Bermuda sod can be planted into late September, and some contractors will even plant it through the winter. Many of us, however, advise against winter soddings.

Digging and dividing perennials. Many of the spring-flowering types will need to be reworked before fall is over, but bulbs would be first on the list, and the digging and dividing must be done in early September, before new root growth gears up for fall. If you have jonquils, daffodils, narcissus, grape hyacinths or species types of tulips that bloom year after-year in your landscape, this is the time to move them.

NEIL SPERRY PUBLISHES GARDENS MAGAZINE AND HOSTS TEXAS GARDENING RADIO SHOW FROM 8-11 A.M. SATURDAYS AND SUNDAYS ON KRLD//1080 AM. REACH HIM DURING THOSE HOURS AT 214-787-1080.

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