Compost, Mulch, and Native Plants: To Use or Not to Use
I have been asked often “Should I add compost or a soil amendment to the soil and mulch to the surface when planting natives?” Or, when I have mentioned that I add compost and mulch, others have stated that they were told to never add anything to the native soil, just plant. This article will address the ‘to use or not to use’ issue and briefly discuss the benefits of composting and using mulch for natives and non-natives alike.
The soil types most commonly encountered in the Nipomo area are sand, clay, and clay combined with fractured sandstone and shale. The sand is from ancient dunes and contains little or no organic matter, nutrients, and tends to be somewhat acid. The clay has a greater amount of nutrients but little organic matter and is slightly alkaline which tends to lock up the nutrients from being available to the plants. The clay, sandstone, and shale combination is about the same as the clay. All of these soils will greatly benefit from the addition of compost and mulch. Let’s first discuss as to why plants need organic matter in their soil.
Picture the rainforest: lush, green, and more plant species per acre than any other plant community in the world. All this when just inches below the forest floor the soil is impoverished. So where do the plants get their nutrients? The rainforest has developed a rapid composting cycle which turns anything, with exceptions, that falls to the forest floor into compost in a matter of a few days. The forest floor teams with microbial and fungal life that breaks down the vegetative and animal matter into basic nutrients that is then taken back up by the roots of the vegetation, nothing is wasted. All the rain, warm temperature, and high humidity play their part in fostering the variety and quantity of microbes and fungus.
Back to the corner of Pomeroy and Willow; this area is a native plant botanical heaven. It didn’t achieve that overnight; the same processes that are at work in the rainforest are at work here. It just takes several years to achieve what the rainforest does in a matter of days. As plants drop their leaves, fruit, or die at the end of their growth cycle, they are slowly decomposed into compost, roots and all. This decomposition releases the nutrients into the soil where it is taken back up by the roots of the vegetation; again, nothing is wasted, literally, a self-sustaining perpetual cycle.
This organic matter in the form of compost is food for the plants and microbial and fungal life. The impact it has on sand is to give it fertility, increase water retention, balance the pH closer to neutral, and support healthy soil populations of beneficial microbes and fungus. These in turn reduce the unwanted microbes, fungus, and harmful plant pests both below ground and on the plants themselves. It also allows the sand to form aggregates (clumpy balls) which increase the amount of air in the root zone and plants do need air for their roots. No air and they die unless they are specially adapted as most water plants are. It has the same benefit for clay except that compost allows for better drainage in clay by opening up the clay structure.
Mulch could be considered the litter under the plants that is in the process of decomposition. If you have oaks, look at the leaf litter under the trees and clear a small area. Dry on top but moist and decomposing near the soil surface. This helps to retain moisture in the soil, keeps the root area cool, and forms a supply of slow release fertilizer to the trees and plants. For best results for the home gardener, this mulch layer should be a mix of green and carbon matter. The green matter can be grass, hedge, or other plant clippings while the carbon matter would by woody chippings, dried leaves, pine needles, or other dry matter. Most important the mulch should be a well mixed combination of the ingredients. This allows air and moisture to penetrate to the soil below and the green matter supplies the nitrogen to the microbes which enables them to break down the carbon matter into nutrients for the plants. Never put a thick layer of one item only, such as grass clippings or leaves (green or dry) around plants as mulch. This will pack down very quickly and become hydrophobic, meaning it will repel water. I have done this on occasion and have found the soil beneath to be as dry as a bone even after a thorough watering of the area. Replenishing this mulch layer as needed will keep down unwanted weeds and continue to provide nutrients to the plant and is an excellent method for recycling your greenwaste.
One method for get these chippings and clippings is to make a small (4 feet by 4 feet by 1 foot high) pile of the ingredients and run your mower over it several times, then mix well, and repeat until the pieces are 1/4 to 1/2 inch in length. Before putting this mulch around your plants, moisten it well. This will keep it from getting blown by the wind and it won’t remove moisture from the soil.
Using compost and mulch for my native and non-native plants with my sand has greatly improved their growth, health, and flowering. As the commercial said, “Try it, you’ll like it”, and you really will.
For a more detailed discussion on the benefits of and how-to for composting, Allyson Nakasone of ECOSLO will be giving a Compost Workshop on a to-be-determined Saturday in August beginning at 9:00 am. Visit the ECOSLO website for the current workshop schedule or call 544-1777 for the date, workshop location, and more information.
