Your March Texas Gardening Checklist

By Skip Richter, Contributing Editor

Vegetables and herbs 

Young and stocky pepper plant

This month brings the last average frost date in most areas of the state. When the danger of frost has passed, our warm-season vegetables, including tomatoes, peppers, eggplant, beans (bush and pole), cucumbers, squash and corn, may be safely planted. Some gardeners gamble a bit and plant ahead of the last average frost date in hopes of getting a head start.

At the beginning of the month, in the northern parts of Texas, you can still get in a late planting of radishes, beets and even some leaf lettuce (for harvesting early as baby greens). It is always a bit of a gamble because, in some spring seasons, hot weather can arrive early.

Mild temperatures have cool-season gardens growing well. With these crops developing rapidly now, take care to harvest at peak quality as a few days can make a difference. Broccoli heads should be tight and full, greens should be young and tender, and kohlrabi should be less than tennis-ball size.

If a late frost threatens a tender crop, a covering can get you through the danger. Denser weights of row-cover fabric and old bed sheets work well. If you use something heavier, you may want to put a support underneath to keep the cover from breaking tender plants.

A milk jug filled with water protects tomato plants against light frost

Water cools off more slowly than air, so a milk jug full of water placed right up against a tomato plant beneath a cover can make enough difference to protect it against a light frost. This may be enough because during a late cold snap the temperature drops to a danger zone for a few hours or less.

Our challenge in the spring garden is to raise a crop in the window between the last frost and the onset of hot weather, which ends the harvest season for many warm-season vegetables, or at least adversely affects quality.

Gambling with an early planting is one way to accomplish this, but another is to start plants in containers indoors. They can be moved outside most days and brought in on chilly nights until the coast is clear to plant them out into the garden.

This is the standard way of growing tomatoes, eggplant and peppers but can also be utilized to get a head start with squash and cucumbers. These latter two just need about two weeks, if indoor conditions are favorable, to grow to a decent size for transplanting. Lighting is the key to good transplants, so plan on using supplemental lighting indoors.

If you are planting warm-season vegetables into the garden early, you may want to hold off on mulching the soil. This allows the soil to warm faster for better early growth. It also means that weed seeds will get a start, but they are easy to remove with a hoe or to mulch over later before they get too large.

Perennials and annuals

Petunias are a popular annual

As the last average frost date passes, our warm-season flowers can go out into the landscape. Some of the favorites for this season include zinnias, begonias, marigold, petunias, coreopsis, cosmos, sunflower, wishbone flower and nicotiana (flowering tobacco).

When planting seed, note the recommended planting depth and spacing. Keep the seedbed moist until the seedlings are up and on their way because seed germinating just below the soil surface is susceptible to drying out, which can ruin a stand before it gets started.

If you are setting out transplants, water them in with a diluted fertilizer solution to help get them off to a strong start. Repeat this application a week later. When the plants have been in the ground for two or three weeks, sprinkle a complete fertilizer onto the soil surface and “scratch” it into the surface inch. Then water the area well. Choose your fertilizer blend based on soil-test results. In the absence of a soil test, a turf fertilizer works fine.

If you are gambling on an early planting, be ready to cover the young seedlings or transplants should a late frost arrive. Leaving the soil un-mulched initially will help the soil warm during the day so that the heat will rise up under the cover on a frosty night, providing extra protection.

Clean up any old dead-growth on perennials. Even if they have started to sprout, you can remove the top-growth back to the ground if the planting is looking unsightly. They will resprout from the base and end up being a more attractive planting in the months to come.

Cool-season flowers are still blooming but at some point will need to be pulled to make room for warm-season color plants.

After pulling the old plants, spread an inch of compost over the beds along with a cup of complete fertilizer (2 cups, if you are using an organic product) per 50 square feet, and then rototill or spade the soil to a depth of 4–6 inches. This will prepare the beds for the next planting of flowers.

When planning your plantings, don’t forget to include some color containers. Containers can add color to landscape areas. Choose containers of adequate size so roots have plenty of soil from which to get water and nutrients as the days warm up. Mix a slow-release fertilizer into the growing medium to provide feeding over the coming few months.

Trees, shrubs and vines

Redbud tree in bloom

Spring-blooming trees and shrubs are putting on a show this month. Notice what is blooming around town and take a visit to a botanical garden. This is still a good time to establish trees and shrubs, so perhaps there are some new additions you’d like to add to your landscape either this spring or next fall.

Woody ornamentals that were planted since last fall are still establishing new roots. Although they may be pushing new, above-ground growth with the arrival of spring, they lack an extensive root system. This first season is the critical one in getting them established.

Hold off on fertilizing them for another month but provide adequate watering. The trick is to keep the soil moist without keeping it soggy-wet for an extended period of time.

Clay soil can be challenging for gardeners

If your soil is a heavy clay, that is all the more challenging because the planting hole can become an “underground bathtub” that holds water long after the surface appears to have drained away.

A 4 to 6”-high, circular berm of soil extending about a foot beyond the original root ball in all directions is a good way to facilitate watering as the weather warms up and demands on the plant’s limited root system increase.

Fill the berm with water and it will ensure that the moisture soaks deeply into the root system. For now, an occasional deep soaking is adequate, but as we move into summer, you’ll probably need to fill it twice a week.

While late winter is the primetime for pruning, if there are some cuts that are really needed, go ahead and make them now. Just take care to not allow the branches to fall and pull away strips of bark, which can happen more readily now with the flow of sap increasing. The three-cut method, which can be found online, is a good way to remove limbs too large to support with one hand while you cut with the other.

Fruits and nuts

Many species of fruit trees and bushes are blooming now. Let’s keep our fingers crossed that a late frost doesn’t decide to spoil the show.

If a frost threatens, take measures to drape a cover over the trees all the way to the ground, and provide a little extra heat underneath them.

For help in dealing with frosts and freezes, see the free publication, Protecting Landscapes and Horticultural Crops from Frosts and Freezes (EHT-048), available at the AgriLife Extension online bookstore.

When using electricity outdoors to provide heat for plants, take care with exposed electrical connections, especially when it is rainy or when organic materials on the surface can pose a fire hazard.

Plum curculios is a pest that requires treating to keep under control

If you have a peach or plum tree that has been plagued by plum curculios in past seasons, begin protective sprays for this pest when the blooms have fallen off. Your Extension office has more information on spraying fruit trees, or you can find a free publication at the online bookstore mentioned previously.

Strawberry harvest begins this month in much of the state. Strawberries don’t ripen after picking, so allow them to reach full ripeness before picking.

If ripe fruit are wet by rain or irrigation, they will tend to decline quickly. This is also a reminder to not wash strawberries until you take them out of the refrigerator to use them. Keep weeds in control now to prevent competition with the plants, which will provide for two or more months of harvesting.

Lawns and groundcovers

The warming temperatures are signaling our warm-season turfgrasses to slowly begin growth. Those cool-season weeds that have been sitting there all winter in the thin areas of the lawn are really taking off.

They are about to enter their reproductive stage when they flower and set seed to provide years of future weed woes for the gardener! Unless the weedy area is extensive, hand-pull them before they produce and release seeds.

Frequent mowing with a bagging attachment can also help remove weeds and their not-yet-developed seeds. This is one of the few times when bagging clippings is recommended!

Have the mower blade sharpened so you’ll be ready for mowing season. A sharp blade puts less strain on the mower and results in cleaner cuts that in turn result in a greener, more attractive lawn.

Don't fertilize early or you will benefit the growing weeds more than the grass, which is not able to take up much of the supplemental nutrients yet. While it is too early in most of Texas, in the southernmost parts of the state by late March, it may be time to put on the first application of fertilizer. 

If your turf is not filled with weeds that have a crop of seeds, the first mowing, where there are still some leaves from your landscape trees on the surface, is worth collecting. This mix of dead leaves and fresh clippings makes a great blend for composting.

Another option is to just mulch it back into the lawn as you mow. Finely chopped organic matter dropped into the turf will decompose fairly rapidly and release nutrients to the growing grass.

Timely tips

Warning! Garden fever is epidemic this month! It causes us to plant more vegetable garden than we can take care of, make impulse purchases of plants that are not adapted to our area (“Because they were calling out to us as we walked by!”) and bring home plants before we have prepared the soil to give them the best chance of success.

We want you to be successful and get the most bounty and beauty from your gardening dollar, so take time to prepare the soil first, learn about the best species and cultivars for your area, and plant them in the most suitable locations in the landscape.

Spring is the peak season for local specialty-plant sales by Master Gardeners, plant societies, community groups and others. Take advantage of these opportunities to acquire plants that are often difficult to find in the trade. You’ll meet a lot of great people in the process.