Building Big-Harvest Soil in Texas

Why it matters

Texas soils swing from sticky clay to loose sand to rocky, shallow ground, and none of them grow big harvests without work. A soil test tells you what to add instead of guessing, organic matter fixes both clay and sand, and raised beds solve drainage. Mulch on top holds water and can boost yields dramatically.

Step by step

1. Get a soil test Take 8 to 10 cores 6 inches deep across the garden, mix them, and send about a pint of rock-free soil to the Texas A&M Soil, Water and Forage Testing Lab. Retest every 2 to 3 years.
2. Pick a sunny, well-drained spot Most vegetables need at least 6 hours of direct sun. Avoid low spots where water stands.
3. Add organic matter On heavy clay, AgriLife suggests working in about 2 to 3 inches of organic matter and 1 to 2 inches of sand, turned 8 to 10 inches deep in late winter or early spring. Don't add more than a 4-inch layer of organic material at once.
4. Raise the beds AgriLife says most Texas vegetables should be grown on raised beds for drainage and air. Even a bed 6 to 10 inches high helps a lot.
5. Keep beds narrow enough to reach Make framed beds no wider than about 4 feet so you can reach the middle from either side without stepping on the soil. Leave 18 to 24-inch paths, or 30 inches if you use a wheelbarrow.
6. Fill the bed right Loosen the native soil underneath 6 to 8 inches deep, blend some of the new mix into it, then fill. Equal parts compost, topsoil-type material and organic matter work; top off as it settles.
7. Mulch everything Lay organic mulch on weed-free soil and keep it about 4 inches deep after it settles. Add more through the season as it breaks down.

Key facts

• Texas A&M's Routine soil analysis tests pH, nitrate-N, conductivity, phosphorus, potassium, calcium, magnesium, sodium, sulfur and boron, and is a base test for fertilizer recommendations.
• Texas A&M routine soil analysis costs $12 per sample (emailed results free; $3 for mailed results), per the lab's sampling guide.
• AgriLife: a well-mulched garden can yield 50 percent more vegetables than an unmulched one of the same size.
• A 4-inch layer of mulch keeps most annual weed seedlings from coming up.
• Gypsum for tight clay: AgriLife lists 3 to 4 pounds per 100 square feet in EHT-076 and 6 to 8 pounds in the Texas Home Gardening Guide; let your soil test guide you.
• Composted manure: 30 to 40 pounds per 100 square feet worked in before planting; never fresh manure.
• Bed soil volume = length x width x depth in feet; a 4 x 8 x 1 ft bed needs 32 cubic feet (about 1.2 cubic yards).
• Clay and high-organic soils hold about three to four times as much fertilizer as sandy soils; sandy soil needs lighter, more frequent feeding.

Texas notes

• Heavy clay (Blackland Prairie, much of East and Coastal Texas): raise beds and add organic matter and sand to improve drainage and air.
• Sandy soils (East Texas, parts of South and West Texas): add organic matter to hold water and nutrients, and feed lightly and often; sandy soils usually need generous potassium.
• Rocky, shallow soils such as caliche areas: build framed raised beds on top and fill them, since tilling deep is not practical.
• Coarse mulches like straw may need 8 inches or more at first to settle to 4 inches.
• Use light-colored mulch in summer to keep soil cooler; never mulch with residue from the same crop you are growing.
• Avoid cotton gin trash unless composted and from a known source, since arsenicals and weed seed can come with it.