May 11, 2013

The Garden Guru: Most critical mid-May tasks

The spring sweet spot has its own to-do list to ensure a bright and beautiful summer landscape

Rants, raves, reviews and resources for Dallas-Fort Worth parents

It’s pleasant working out in the landscape and garden this time of year, which is a good thing, because there are several important tasks that really must be addressed now if you hope to have a successful gardening season.

Prune spring-flowering shrubs and vines. These plants produce their flowers on the prior season’s growth, so by reshaping them now, you give them an entire season to fill back in. This is not a requirement, but if pruning is needed, this is the time. Plants would include azaleas, wisteria, forsythia, quince, bridal wreath, Carolina jessamine and Lady Banksia roses.

Start new turf. Soil temperatures are finally warming. Daytime temperatures aren’t as hot as they will be. Mid-May is the best of all worlds for seeding, sodding, plugging and hydromulching. Consider your turf choices carefully. Lawns aren’t easy or inexpensive to plant, so you want the very best grass for the situation.

Replace turf that has thinned because of shading. St. Augustine is our most shade-tolerant lawn grass. However, even it must have five or six hours of direct summer sunlight each day if it’s going to succeed.

To be candid, I get frustrated when people (even friends) ask how to cope with the shade, then ignore my warnings that they don’t have enough light for any grass to survive. I’ve lived this same story for 37 years in my own lawn, and I’m very secure in what I’m saying: You need to make plans for shade-tolerant groundcovers and shrubs if you don’t get five or six hours of direct sunlight. Thinning the trees often ruins their looks. Trust me on this one.

Fertilize most of your plants. Now that it’s finally warming, almost all of your plants are starting their growth spurts. This may be a surprise to some, but almost all of our soil tests come back showing that every plant that we grow in our black clay gumbo soils needs only nitrogen. Select a quality high-nitrogen or all-nitrogen food. Apply it uniformly, and water it in deeply.

Shop nurseries for the very best selections of the season. Annuals and perennials never looked better. Herbs are plentiful, and shrubs and trees are fully leafed and growing vigorously. Independent nurseries in particular are likely to have the unusual types of plants that make your garden unique and enchanting, and those less-common plants tend to sell out very quickly.

Wrap the trunks of new red oaks and Chinese pistachios. These trees have very thin bark, and for their first year or two in your landscape, they’re going to be vulnerable to sun scald and borer invasion. Applying a paper tree wrap from the ground up to the lowest branches is inexpensive, unobtrusive and highly effective.

Fill low spots in the lawn. Since grass is starting to green up and grow, this is a good time to address any small depressions within the turf. Dry sand (“brick sand,” as you might use in mixing mortar) works best. Spread it out on the driveway to dry for a few hours, then spread it, shovel by shovel, into the low trenches and holes. Let it filter through the runners. Use the back of the shovel to level it off smooth, then sprinkle it lightly to settle it in. If the holes are deeper than one inch, or if they’re wider than 5 or 6 inches, you may want to use topsoil that you’ve collected elsewhere in your landscape or garden.

Be careful in introducing fresh topsoil from a soil and gravel vendor into your garden, since it may contain weeds, specifically nutsedge.

Apply systemic insecticide if crape myrtles are showing scale populations. This pest doesn’t do a lot of damage to the crape myrtles, but it makes them unsightly. It was first observed in northern Dallas and southern Collin counties in 2004, but it is now appearing in Tarrant and Denton counties and elsewhere. Look for 1/8-inch-long elongated white scales on the trunks and twigs. Texas A&M research has shown that a systemic drench of Imidacloprid applied in mid-May is the best means of preventing or stopping it. Left unchecked, it leads to sticky honeydew and black sooty mold.

Eliminate aphids from tender new growth. If you’re seeing masses of green, yellow, black, red or white pinhead-size and pear-shaped insects on tender new growth of your plants, those are aphids. Wash them off with a hard stream of water, or apply a general-purpose insecticide spray to them. Systemic drenches work well, but they take a couple of weeks to be effective.

Address iron deficiency in shrubs. This appears as yellowed leaves with dark green veins, most prominently on the newest growth first. Affected plants will start by showing light green leaves, then the yellowing, then browned and dead branches. It’s most common on azaleas, loropetalums, wisterias, cherry laurels, some hollies and even nandinas. For most of these plants, an application of iron in tandem with a sulfur soil-acidifier will help green them back up. However, you’ll need to repeat the treatment several times during each growing season.

Keep iron sprays and granules off concrete and stone, since it leaves rusty stains. And an important note: It is impossible to get enough iron into the tissues of large shade trees (water oaks, pin oaks, East Texas pines, etc.) to correct iron deficiency. The process is too expensive and in most cases, you won’t see dramatic results. That’s even true with tall acid-loving hollies like Savannah, East Palatka and Foster.

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