Gardeners from other parts of the country are often horrified at the growing conditions here in the Big Country. Our difficult soils produce shudders even from seasoned gardeners in other parts of Texas. Compost and mulch are the dynamic duo that address many of the issues that make our soils so unfriendly to plants. That makes them the closest things to superheroes that serve those of us who love plants.
Soil: A healthy soil has about 50 percent solid matter, 25 percent air space and 25 percent water, with organic matter making up 5 percent of the solid matter. It has rich color, a great earthy smell and a crumbly texture and is teeming with life.
Our soils, by contrast, range from heavy clay to the finest of sand. Texas heat burns organic matter up before it can be incorporated into the soil. This translates to less than half of 1 percent organic matter, the life blood of soil. Dirt may be hard and dense or run through your fingers.
Compost: Compost is simply decomposed organic matter. You can buy in bags or in bulk from stores. Look for a quality product that is dark, smells like great soil and does not look like the parent material. Or, make your own compost (I’ll have a column soon). Till a 3-inch layer of compost into the soil.
What benefits can you expect? Those tiny particles of clay that make it so dense will loosen some with the addition of compost, allowing better movement of air and water in the soil. Add it to a sandy soil and the same product will help hold the sand together, increasing its water-and nutrient-holding capacity. The compost is full of microorganisms like fungi and bacteria that provide nutrition for growing plants. It reacts chemically with soil to help buffer the typically high pH of most of our soils (measure of alkalinity or acidity) that can bind up needed plant nutrients.
What if you have established plantings? Top-dressing with compost will still be beneficial. The process will just be slower.
Mulch: Mulch is used to cover the soil. It can be inorganic like rocks or organic. Wood chips are the most popular organic mulch, though not the only option. Both will help prevent erosion and inhibit weed growth.
Rocks might be a good choice in a very xeric bed with cacti and other heat-loving succulents. They will appreciate the protection provided from standing water and the heat-holding capacity of the rocks. You will feel the extra heat, too, so keep that in mind.
For most uses, an organic mulch is much preferred. A two- or three-inch layer of coarse wood chips will help maintain soil moisture that would otherwise be lost to evaporation and help moderate soil temperatures. As the mulch degrades, it acts as a very slow-release fertilizer, adding nutrients and yet more organic matter to the soil. Since the soil does not heat up as much, more beneficial organisms like the amazing earthworm remain active in the root-growing zone.
When mulching woody plants, don’t mound the mulch around the trunk or stems of the plant. That creates an unhealthy environment for the plants. Think doughnut, not volcano.
Search txmg.org for the “Take Care of Texas” guide to mulching and composting. If you have questions about this or any other gardening topic, please call the Big Country Master Gardener Association’s hotline at 325-672-6048, or email us at [email protected]