Mulch It Up! Choosing the Best Mulch for Your Garden


“I have a large vegetable garden – What would be the best mulch to use (if any)? Every year, the weeds get the best of me and I need something that works, without being expensive.

~Sarah”

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Hi Sarah,

Thank you for your question! There are a number of inexpensive and simple items you can use for mulch.

The first thing you need to determine is whether you want to go with an organic or inorganic mulch.  In this case, by organic/inorganic, I am refering to whether the mulch is comprised of carbon molecules (organic) or lacking in carbon molecules (inorganic) — not organic versus convention.  We will get to the great organic/conventional debate later.

Many folks choose to go with a number of inorganic mulches. These include:

–Plastic (usually black)

–Gravel or stones

–Geotextiles (landscaping fabric)

–Newspaper (surprised this is here? See note below)

There are a number of people that use these every day and will tell you that these are the best options out there.  However, I disagree. While these may be incorporated into a landscape and provide a seemingly maintenance free garden, they also cause a LOT of problems for a home gardener, including:

–compaction of the soil by too much weight on top of the roots of a plant.  This prevents proper root growth and root aeration. (stones/gravel)

–reduced availabilty of water and air exchange that adversely affects both the plant and the microflora and microfauna that are in the rhizosphere (‘root zone’). (geotextiles and plastic)

–difficulty in removing unwanted weeds and soil after the mulch has been there for some time. (stones/gravel)

–weeds with nuisance root systems (quackgrass, dock, dandelion) imbedding themselves into the mulch. (geotextiles, plastic)

–releases unwanted/unsafe chemicals into your soil. (high levels of dioxin in newspaper, high levels of biphenyl (BPA) in plastic)

The best way to go, in my opinion, is with an organic option.  Instead of introducing a foreign, inorganic substance to your garden, you are adding a feature to your garden that has a dual purpose: controlling weeds and feeding your plants.

There are two cardinal rules for using organic mulches to combat weeds. First, be sure to lay the mulch down on soil that is already weeded, and second, lay down a thick enough layer to discourage new weeds from coming up through it. It can take a 4- to 6-inch layer of mulch to completely discourage weeds, although a 2- to 3-inch layer is usually enough in shady spots where weeds aren’t as troublesome as they are in full sun.

The most common types of organic mulches are:

–Grass clippings.  Grass clippings are readily available mulch that can be gathered with a bagger on the mower or by raking. It’s fine to collect grass clippings occasionally to use as mulch, and the nitrogen-rich clippings are an especially good choice for mulching vegetable gardens. Your vegetables will thank you for the nitrogen boost!  The only caution would be to make sure that the clippings are coming from grass that does not have weeds growing in it that may be going to seed, like dandelions.

–Leaves.  If weed control is your goal, shredded leaves are your star pupil! Leaves from just about any deciduous tree work well. Contrary to popular belief, leaves such as oak will not acidify the soil. Oak leaves are acidic when they are fresh, but they lose this acidity as they decompose. To keep the whole leaves from blowing away or forming an impenetrable mat, coarsely shred or chop them (running them over with a lawn mower is an easy way to do it). Like grass, leaves should be spread 2 inches deep and replenished as needed. When you dig into soil that’s been mulched with leaves, you’ll find lots of plump earthworms, who thrive on turning them into the best fertilizer for your garden.

–Straw. If you are buying straw for mulch, be sure you get straw and not hay. Straw has just the stems of plants; hay has the seedheads, which will sprout into weeds in your garden. Straw breaks down quickly, adding nutrients to the soil. Because straw does not mat like grass or leaves, you can pile it 6 to 8 inches deep in your vegetable beds and strawberry patch. Climate concern: In very rainy climates, avoid straw mulch, because wet, partially rotting straw makes a perfect hideout for slugs.

–Cover crop. Plants such as hairy vetch or alfalfa that you grow specifically to improve your soil—sometimes called green manure—are effective as mulch, too. CAUTION: Do not let hairy vetch produce seed, as it will sprout where you don’t want it.

–Bark or wood chips. Typically sold as chips, nuggets, or shredded pieces, wood decomposes slowly but stays in place well (pine bark nuggets may float in a heavy rainfall). You’ll find both hardwood and softwood options. Common hardwood types include hickory, oak, and elm. Softwood bark, such as pine, fir and redwood, decomposes more slowly than hardwood. Coarse-textured mulches like bark can be layered up to 4 to 5 inches thick, because more air circulates between the bigger particles and water passes through them more easily than it does with finer-textured mulch like grass or leaves. Watch your wallet: Bark mulches can be expensive to use in large areas.  You can find tree and utility companies, arborists, and yard-waste facilities willing to give you wood chips for free. Wood chips are a good choice for paths and where you have a lot of ground to cover, but don’t use them close to your house, because termites and other destructive insects may be living in them. CAUTION: A popular low-cost choice for landscaping is a recycled mulch made from construction wastes and wood pallets. Keep this away from your vegetable garden, as it may contain unknown industrial contaminants.  Also, do not use colored chips or bark in a vegetable garden, as the paint used on the chips/bark is not safe for food production.

–Compost. If you have enough compost, it’s fine to use it as a mulch. It will definitely enrich your soil and make your plants happy, but keep in mind that when any kind of mulch is dry, it’s not a hospitable place for plant roots. So you may want to reserve your compost to spread as a thin layer around plants and top it with another mulch, such as chopped leaves. That way the compost will stay moist and biologically active, which will provide maximum benefit for your plants.

If you choose an organic type of mulch, the last thing you need to decide is if the mulch is organic or conventional.  If the mulch is coming from something you have grown or composted, you already know everything about it.  However, if you are purchasing the mulch, make sure that what you purchase fits with the type of garden you have.  Nothing like growing an organic garden only to find out that your mulch came from an area that was heavily sprayed with chemicals.

I hope these ideas help you out.  Let me know what you use and how it goes!

 

© Mertie Mae Botanics LLC and Horticulture Talk!, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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