Q. Our back yard is landscaped with mostly rhodies, azaleas, Japanese maples and a variety of other acid loving plants. The whole area is covered with bark. The problem is that water seems to have a hard time penetrating the bark. Often after watering I will check the moisture and the soil beneath the bark will hardly be wet. The plants are suffering from lack of water. How can I improve this situation? Mardell Rediske – Puyallup, WA
A. The most likely cause for this situation is that the mulch is to thick and/or to fine textured. When the proper mulch is applied at the proper thickness it will allow water as well as air penetration to the roots below (roots breath oxygen too!) while simultaneously moderate soil temperature, reduce the impact of irrigation and raindrop impact, reduce evaporation of soil moisture and suppress weed seed germination. It is one of the foibles of human nature to think that if a little is good then more is better. But if mulch is applied too thickly water and air exchange will be compromised. Coarse mulch has more space between the mulch particles and therefore will allow for better water penetration and air circulation than finer particle mulch. Mulch should be from two to four inches thick to work effectively. Coarse mulch can be applied at the higher end of the range and fine mulch at the lower end of the range. Mulch is reapplied each year to replace that which is lost each year due to decomposition. So what can also happen is that mulch is reapplied without testing the depth of the existing mulch. After a few seasons the mulch depth is too deep. If you find that your mulch depth is ideal then not enough water is being applied. Use a water can or rain gauge to measure the amount of water being applied. One inch per week is usually sufficient.