The start to 2020 has included quite a few weather “ups and downs” to say the least. If there is one gardening practice we can use to help plants experience more consistency despite the weather, it is the practice of proper mulching. Mulch provides many benefits that help plants cope with a stressful environment. Mulch provides a more consistent soil temperature, reduces water losses from the soil due to wind and evaporation, reduces soil erosion, compaction and crusting and helps stop weeds.
Be aware, though, that as with any practice, a little is good, but too much can cause problems very quickly. Here are some tips to follow as you prepare to mulch around your plants this season.
The ideal time to apply mulch in flower and vegetable gardens is late spring after the soil has warmed up. Most mulches slow the warm up of the soil, which is a good thing during the heat of the summer, but applying mulch too soon may hinder vegetables such as tomatoes or flowers like lantana that require warmer soil to grow well. Mulch may also need to be replenished in existing flower beds or around trees with a new fresh layer.
Three best practices
1. Keep mulch away from tree trunks and stems of woody shrubs. Contact between mulch and woody plant stems can foster diseases/bark damage and provide insect and rodent cover. Too much mulch piled up around a tree or shrub can confuse it into thinking the soil level has actually changed, which may lead to an attempt to grow roots into the mulch or even cause the start of decay in the outer bark.
The distance to keep mulch away will vary with the size of the plant. On a large tree an entire 8 to 12 inches should be left bare between the mulch and the flare roots of the tree. On a tomato vine, a distance of 1-inch bare space is just fine. Mulch as much of the root zone as is practically possible. In a perfect world, a tree would prefer its entire root system to be mulched, but in most real-world cases it is only possible to mulch out to several feet away from the tree trunk or whatever is practical on the site.
2. Organic mulches are preferred. While rock mulch can last a long time, it also increases the heat around the home and landscape plants. Organic mulches like compost, wood chips, straw, old shredded leaves or grass clippings reduce heat and also decompose to add valuable organic matter to our Kansas soils, which benefits plants for years to come.
3. Depth is important. Applying mulch too deeply is actually counter-productive and can be worse than a layer that is too shallow. Mulch applied too deeply can prevent moisture from reaching the soil. A light quarter-inch of rain may not even get to the soil through a thick layer of fine mulch. Too much mulch also prevents oxygen from getting back into the soil after the plant uses the water. Plants need to breath just like we do, and suffocation of the roots will result in plant stress and even death. The proper depth to mulch depends on the material. Finer mulches such as grass clipping or compost are best applied at a depth of around 1 to 2 inches. Bulkier mulches such as larger bark chunks should be 3 to 5 inches deep. For most products including bagged wood mulches, a depth of about 3-4 inches is optimum.
Jason Graves is the horticulture Extension agent for the Central Kansas District.