Mulch inhibits weeds and conserves soil moisture. However, many gardeners don’t use mulch in their vegetable beds. Here’s the lowdown on which mulches to use and how to use them.
Nobody likes dirty pumpkins, so growing them on a rye mulch keeps the fruit nice and clean.
When you mention mulch, the first thought that comes to most minds is the aesthetic look of it in the landscape. A nice, dark bark mulch makes the plants in the bed standout a bit more, but mulch is more than looks. Mulch also inhibits weed growth and conserves soil moisture. While aesthetics are not as big of a concern in the vegetable garden, the other benefits are equally or more important to backyard vegetable growers.
Almost anything could be used to mulch your vegetable plants and many choose whatever is readily available. One that is easily at hand for me is grass clippings. I apply a 3-inch layer of grass clippings around my plants and it soon mats down to create a nice barrier for weeds. It does smell a bit at times as it decomposes. A word of caution here, do not use grass clippings that have been treated with an herbicide (and that includes lawn fertilizers that have herbicides incorporated into the fertilizer). There are several products that can carry over onto the clippings and affect your vegetable plants.
I live in an area that is heavily wooded and contains a number of sawmills that cater to forest landowners. Sawdust is readily available at times and can be cheap. A 2-inch layer of sawdust can give good weed control and keep moisture in the ground. Be aware that microorganisms that start breaking down the sawdust need nitrogen to complete the process and will take it out of the soil (and away from vegetable plants). Since this mulch contains a lot of carbon and very little nitrogen, a little bit of extra nitrogen should be added to help those microbes in the decomposition process.
In addition, if straw is readily available and cheap, it serves as excellent mulch for vegetable plants. Other plant-based mulching options could include leaves (be sure to avoid black walnut leaves), bark and woodchips.
Maybe you don’t have a big enough lawn to produce large amounts of grass clippings or any nearby sawmills with excess sawdust — you still have access to a very cheap and readily available mulching material: newspapers. Newspaper is allowed in organic operations as long as you stay away from the colored inks and glossy prints. Newspapers can be picked up from neighbors and friends who are looking to getting it recycled. Something will have to be placed on top of the newspapers to prevent them from blowing away.
Some technology that is used in commercial vegetable production is making its way into backyard gardens. For the past several decades, commercial growers have utilized black plastic mulches to gain moisture-saving advantages and weed control. In addition, the plastic generates warmer soil temperatures, which allows for a bit earlier planting. These advantages have led to larger yields, earlier harvests and cleaner fruit (fruit no longer sits on bare soil).
Researchers, in the past several years, have looked at crop response to different colored mulches and how growers (both commercial and backyard) can use this to their advantage. Different colored mulches affect the soil temperature a bit but they also reflect different wavelengths of light back into the plant canopy, which in turn alters plant growth and development. At Penn State’s Center for Plasticulture, they looked extensively at numerous colors of plastic and the plants’ responses.
Yield increased by about 12 percent with Solanaceous crops such as eggplants and tomatoes when grown on red plastic compared to black plastic. In addition, earliness of yield is also increased on tomatoes. One interesting response by tomatoes to the red mulch is that it had the least amount of foliage compared to other mulches (silver, white and black). This might be helpful in disease management in that less foliage means better air circulation and drier leaves. Many of our tomato diseases such as early blight and septoria leaf spot need that humid, wet environment commonly found in a densely foliated tomato plant.
While tomatoes performed well under red mulch, cucurbits such as summer squash, cucumber and cantaloupe yielded 20, 30 and 35 percent more fruit respectively when grown on dark blue mulch than on standard black plastic.
Clear plastic is generally not recommended as it allows light to penetrate and promotes weed seedling germination under the plastic. Note the weed that is growing under the clear plastic, between the two eggplants.
While some gardeners may not like the idea of using plastic because of disposal issues (commercial growers face the same problem since it costs $25 to $100 an acre for labor and disposal of plastic mulch) there is an effort to create biodegradable mulch that acts like plastic mulch. These mulches are mostly made of corn and wheat starches that will break down in carbon dioxide and water from soil microorganisms. Keep your eyes open for this stuff in the near future.
Some ambitious gardeners are using cover crops to help minimize weed pressure and conserve soil moisture. This mulching system is ambitious because the mulch is actually put in place the year before vegetables are transplanted into the garden. Winter annual crops, such as rye, are planted in late summer or early fall and allowed to grow into the following spring. At that time, the cover crop is killed by undercutting, mowing or spraying with an herbicide. It is then rolled or flattened to create a mat on the soil surface. Vegetables are then transplanted into the field. Although this mulch will break down during the summer, it will give the vegetables a huge head start over weeds and allow the vegetables to out-compete weeds for light and nutrients.
Rows of snap beans planted in a rye crop that was killed and rolled to create a mulch on the soil surface.
The use of mulch in your garden is too advantageous to ignore. You can relieve moisture stress, increase yield and earliness, have cleaner fruit, and yes — even have an aesthetically pleasing garden. Your only limitation is deciding which mulch you want to use.
From State-by-State Gardening July/August 2013. Photos by Tom Butzler.