By Missy HodginTexas AgriLife Agent
Given the time, effort and money required for most landscape projects, it’s important to get off to the best start possible. That begins with proper soil improvement. This certainly is not the most exciting or glamorous aspect of a landscape project – but it may be the most crucial for ensuring long-term success.
Proper soil preparation begins with an assessment of the current physical and chemical characteristics of the soil(s) you will be working with. More often than not gardeners usually think about the chemical aspects first such as fertilizers, root stimulators, soil additives, etc. Sure these are important, but it’s the physical properties of a soil that can make or break a landscape planting. For optimum growth, plant roots need a good balance of air and water. These characteristics are determined by the soils aeration, drainage and water holding properties.
So why is this important? Landscape soils that hold too much water typically result in landscape plants having root health problems. A significant lack of oxygen in the soil can result in root disease, nutrient deficiencies, deterioration of root systems, and ultimately plant death.
Landscape soils that do not hold adequate water require frequent irrigation, subject plants to drought stress and possibly damage from salt buildup.
One of the best ways to determine a soils aeration, drainage and water holding capacity is to conduct a “hole-test.” The basic steps are as follows:
- Using a post-hole digger or sharp shooter shovel, dig a hole 6 to 8 inches in diameter and 2 feet deep
- Fill the hole approximately half-full with water. Note the time
- Determine how long it takes for the water to drain from the hole
Less than 15 minutes means excessive drainage. Consider adding organic matter to increase the soil’s water holding capacity.
Fifteen to 30 minutes means adequate drainage and water holding properties. Modifications are not required for planting trees, but adding organic matter will still benefit most landscape planting for flowers and shrubs.
Thirty minutes or more means poor drainage. Consider raised beds or incorporating coarse textured soil amendments (compost, bard mulch, expanded shale) to increase aeration and drainage.
Some additional tips regarding landscape soil improvement include using organic matter that is thoroughly decomposed (compost, bark mulch). Raw wood materials such as shavings and chipper material require nitrogen to break down and often out-compete plants for available nitrogen in the soil. This can result in weak, stunted growth. If raw materials are used, additions of nitrogen fertilizer will reduce the negative impact on plants.
The best organic matter for use in landscape soils has a good distribution of coarse and fine particles, ranging from pea-diameter to pencil-sized pieces. The finer the organic matter, the greater the water holding characteristics.
In some situations it will be more beneficial to construct a raised bed to achieve the optimum physical characteristics for plant growth.
Soil improvement can be the most time consuming part of a landscape project. And when the task is complete, few people will appreciate the effort spent on this project. However, the results are typically worth the investment in terms of overall landscape performance, water conservation and long-term success.
For more information about this topic or for more information about raised bed gardening contact the Texas A&M AgriLife Extension office, Clay County, at (940) 538-5042.