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Mulch - What Is It and Which Mulch Should You Use Where?
What Is Mulch and Which Mulch Should You Use Where?
By Marie Iannotti
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Using Shredded Bark as a Mulch
Using Shredded Bark as a Mulch
Photo: © Marie Iannotti (2007) licensed to About.com, Inc.
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What is Mulch?
Mulch is any type of material that is spread or laid over the surface of the soil as a covering. It is used to retain moisture in the soil, suppress weeds, keep the soil cool and make the garden bed look more attractive. Organic mulches also help improve the soil’s fertility, as they decompose.
Examples of organic mulches include:
Bark, Shredded or Chipped
Organic mulch will decompose and have to be replaced, however in the process it will also improve your soil’s fertility and, of course, its organic content. Generally the dryer and woodier the mulch, the slower it will decompose and the less nutrients it will give to the soil.
It pays to know the origin of manure, compost and straw, since these materials can contain viable weed seeds. The last thing you want is to spread a mulch that is going to start sprouting.
Uses for Organic Mulches:
Bark mulches are best used around trees, shrubs and in garden beds where you won’t be doing a lot of digging, like front walkways and foundation plantings. These woody mulches don’t mix well into the soil and it can become a hassle to have to keep moving them aside to make way for new plants.
Compost and Composted Manure can be used anywhere, as long as they are relatively well composted and weed free. You can use them as a coating of mulch or simply side dress plants with them during the growing season, to insulate and give a boost of slow released nutrients.
Grass Clippings are a mixed bag and are best suited to remote areas of your garden where you basically want to suppress weeds. Grass clippings, like most green plant debris with a high water content, decompose very rapidly and in the process they can get somewhat slimy, with an unpleasant odor - so use with discretion. Grass clippings also tend to mat down and not allow water to pass through.
Ideally you should use a mulching mower and leave the clippings on the lawn to add fertility to that soil. However if you do bag your grass clippings, don’t throw them away unless you have used weed killer or some other pesticide on your lawn. Synthetic lawn care products can be bad for some flowers and you certainly don’t want to use them in your vegetable garden. But untreated grass clippings can either be dumped into your compost bin or used to mulch open, unplanted areas.
Newspaper as mulch is becoming more and more popular. Most newspapers have switched over to organic dyes, especially for their black & white sections. Shredded newspaper has been used for years to keep plant roots moist while shipping. Layered sheets of newspaper also have great moisture retention abilities and they act like other organic mulches as far as suppressing weeds and controlling soil temperatures. They are also great for smothering existing grass, to jump start a new garden bed.
To use as a mulch in the garden, spread a layer of 4 - 8 sheets of newspaper around the plants. Moisten the sheets to keep them in place. On windy days it’s easier to moisten the sheets before you place them down. Cover the newspaper with a 1-3 inch layer of another organic mulch and the weed protection should last throughout the growing season.
Shredded Leaves are natures favorite mulch. Shredded leaves can be used as mulch anywhere and have the added bonus of being free. I have never had so many earth worms in my flower gardens as I’ve had since I started using shredded leaf mulch about 3 years ago. Even my compost pile doesn’t have as much activity as under these leaves.
Some gardeners don’t like the look of leaves in their garden and they probably aren’t appropriate for formal gardens. But if you spread a layer in the spring, before plants spread out, the leaf mulch tends to blend into the view within a short time. Shredded leaves are perfect for woodland gardens and I always spread a layer over my vegetable garden in the fall, to begin decomposing over the winter.
Unshredded leaves can mat together and repel water, in rainy areas. But I have to confess that if my leaves get too wet to shred, I’ll use them as mulch anyway and simply stir them up a bit if they appear to get matted.
Straw and Salt Hay are popular mulches for the vegetable garden. They keep the soil and soil born diseases from splashing up on lower plant leaves and make paths less muddy. Straw decomposes very slowly and will last the entire growing season. It also makes a nice home for spiders and other beneficial insects who will move in and help keep the pest population in control. And finally, it’s easy to either rake up or work into the soil when it’s time to plant a new crop or put the vegetable garden to bed.
Examples of Synthetic and Inorganic Mulches:
Synthetic and Inorganic mulches do a goo job of holding moisture and blocking weeds. They don’t add any fertility to the soil, but on the other hand, they don’t decompose and require replacing as often as organic mulches.
Uses for Synthetic and Inorganic Mulches
Plastic and Landscape Fabric are good choices for around foundation plantings and other shrubs and trees. These plants don’t require frequent fertilization and, for the most part, you won’t be working in these beds regularly and so you don’t want to have to worry about weeding them throughout the summer.
However plastic gets very hot in the summer and besides smothering weed seeds, it can also kill all the good things in the soil, including plant roots, unless there is sufficient moisture. Be sure to cut holes in the fabric to allow sufficient water to pass through. If you are seeing puddles accumulate on top of the plastic or fabric, you don’t have enough drainage. Landscape fabric is porous and shouldn’t be a problem unless it gets blocked.
If you like the functionality of plastic or landscape fabric, but not the look, you can always add a thin layer of bark mulch on top of the plastic or fabric for camouflage. However, as the bark decomposes, weed seeds will be able to take hold on top of the plastic or fabric. You will also need to replace the bark as it disintegrates.
Tip: If you’re building raised beds, consider making them the width of your plastic or fabric so that you can cover the bed without seams.
Gravel and Stone work well as mulches in areas that require good drainage and/or beds with plants that like a little additional heat, like Mediterranean herb gardens and rain gardens. Stone is hard to remove, so give it a lot of thought before using stone or gravel as a mulch.
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