Great soils are the foundation you need to make your trees grow. Austin is blessed with many gifts; however, the gift of good soil is not of them. There’s black clay in Pflugerville and many hillsides west of I-35. They’re dense and they absorb water slowly and pack tightly. This makes it tough for trees and plants to get a foothold in the soil.
To the west, we have limestone outcroppings covered with thin soil. Thin soil makes plants and trees susceptible to drought because roots quickly deplete the limited moistures of these soils. Along the river bottoms and the broad plains to the southeast of town, the soil is deep loam. This type of soil absorbs and drains water well. It provides a good foundation for growing plants and trees. However these soils, like all soils in the region, are low in organic matter.
As a general rule, if you want to grow things in Austin, you need to improve the soil. The two main things you need are compost to improve the soil’s quality and more soil depth to support a strong, extensive and resilient root system. A soil depth of 6” is minimal for lawn grasses. More is better. Turf that is grown on more shallow soils is weak. It requires constant watering just to keep it alive. Flowers and vegetables need about 1 foot of soil to grow well. Trees can require more than that.
You can buy or make compost to put on your soil. If the soil is deep enough and just needs some improvement, spread several inches of compost over the area you need to improve. You’ll want to mix it as deeply as you can. This will enhance the soil in the root zone of the plants or trees and improve your results dramatically.
If the spot is poorly drained or has a thin soil over underlying rock, you may need to bring in a special soil mix to build up your depth. These mixes come in many variations and usually have a blend of loam and sand along with composted bark, manure or other decomposed organic matter. Spread it out over a few inches and then till or spade it into the existing soil. Then spread more over the area to build up the soil to the desired depth. This blending technique will prevent the dramatic interface between two types of soil that can impede root penetration and could create a “perched water table” because water will not readily move from the loose, compost-enhanced mix into an underlying clay layer.
For more information on soil types in Travis County, visit: http://www.nrcs.usda.gov/Internet/FSE_MANUSCRIPTS/texas/TX453/0/Travis.pdf. If you have any questions about our tree’s health, feel free to contact us at Austin Tree. We can be reached at 512-341-8888.