Mulching with Organic Materials in the Small Community Garden: A View into How GrowLocal Urban Gardens Network Mulches

Mulching
            Even if not considered the most exciting part of gardening, mulching can be a simple source of many benefits. Some benefits of mulching are weed suppression, soil moisture retention, increased soil organic matter, temperature regulation, erosion reduction, decreased soil compaction, and the improvement of a garden's appearance, among others. Mulch supports the soil health principle of keeping the ground covered and is commonly defined as any plant or suitable material applied to the land surface. In other words, almost any material used to cover the ground could be considered a mulch, and could be synthetic or organic. There is often interest in organic mulches since these materials are frequently available on the farm. Plant residues, leaves, grass clippings, and newspapers can be recycled and used as mulch. Straw and hay can be purchased or otherwise sourced to use as mulch. These materials can also be left on the ground at the end of the growing season. In addition, since organic mulches are in close contact with the soil, they can also help increase soil organic matter (as they break down) and serve as a source of carbon and nitrogen that impact the soil's nutrient availability.
           There are a myriad of ways in which gardeners use organic material mulches. Typically, if transplanting, mulch is placed on the growing bed before, and if directly seeded, the mulch is added when the crop plant is well established. Some growers plant cover crops that winterkill (e.g. oats), and then space is made between the crop residue to direct seed in the spring. However, there are ways to incorporate mulches without long-term planning. For example, plant residues can be laid on walkways to reduce soil compaction, and tree leaves placed on top of beds (preferably composted). Another way of mulching is to put down newspaper on top of the soil before adding straw mulch. This method helps increase weed suppression. These are a few examples, and if you have doubts or questions about a specific material, reach out to your local Soil and Water Conservation District office. 

Footbridge Sharing Garden in Lafayette, Indiana. Information about GrowLocal mulch practices was provided by Harry Smith.

​How GrowLocal Urban Gardens Network Mulches
           GrowLocal Urban Gardens Network –a garden network in the greater Lafayette, Indiana area– uses two different mulches at a couple of their gardens. One of the growers and garden managers, Harry Smith, uses wheat straw and wood chips donated from various sources. Harry applies wheat straw for annual crops and wood chips for permanent walkways and perennials, including fruits, trees, bushes, nuts, and berries. For Harry, the benefits of mulching go beyond the before mentioned (e.g., weed suppression, moisture retention…). Harry said: "Most of our lots were developed with buildings at some point in their history.  The result is soil containing many urban artifacts: rock, brick, concrete, metal, and even asphalt. These solid materials at or near the surface absorb and hold heat, accelerating soil surface moisture loss and increasing the need for irrigation. Mulching puts these solid materials in the shade and keeps them cool." He described this process as "Making peace with the rocks."

​Some considerations

1. If moisture is high below the mulch, it could attract slugs.
2. With transplanted crops, leave a couple of inches gap between the crop plant stem and mulch to prevent stem rot.
3. In the spring, organic mulch should be applied when the soil has warmed up.
4. Beware of black walnut or black locust leaves. They contain the chemical juglone and can inhibit growth of some crop plants (this process is called allelopathy). 

Additional Resources 
IASWCD Urban Soil Health Program Website 
NRCS - Mulching Tip Sheet
​Missouri Botanical Garden - Mulching Publication 
Marion County SWCD - Mulching Publication 
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​Article written by Marian M. Rodriguez-Soto, Regional Urban Soil Health Specialist for the Urban Soil Health Program-a contribution agreement between NRCS and IASWCD. 

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