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Choose mulch carefully and your plants will thank you

By Mary Collister Gardening
Published October 19, 2007


An article I read recently got me thinking about mulch. I'll get back to the article a little later, but it's probably a good time to review what we know about mulch.

Neatly mulched beds improve the appearance of almost any landscape and provide a variety of other benefits. A thick layer can help protect plant roots and add nutrients to the soil as the mulch decomposes. Mulch will also help slow the erosion of topsoil. It may also help decrease the amount of weeds growing in the beds and retain moisture.

There are both organic and inorganic mulches and you must choose the best material for your garden. Proper application also increases the benefit of the chosen material.

Organic mulches are derived from natural sources and will improve your soil as they decompose. You'll see a number of options used in our area.

Compost will give you the best results if you are trying to improve your soil. Your plants will love it, but, of course, so will any weeds. If compost is not completely decomposed when added to your bed it may not be as attractive as you would like. Some gardeners prefer to add compost as a soil amendment and then spread another mulch on top of the compost for aesthetics.

Lawn clippings are an organic mulch available to most of us. Make sure they are dry before you add them to your beds. If not, you will end up with a matted mess that may be impervious to water. And don't use lawn clippings from a yard that was treated with herbicide. The best bet is to add the clippings to your compost pile or use them in a vegetable garden, as they are rich in nitrogen.

Leaves are plentiful in our area, especially oak. And they are free. They will look and function better if they are partially decomposed or shredded. I just let the leaves fall where they may in my back beds but they do have a tendency to blow and I'll see some areas with a much thicker layer than others. This probably would not work well in more publicly visible areas. Matted leaves can also form a barrier that repels moisture and air. I do move the leaves around often using a rake.

Wood chips, sawdust or shavings can be visually pleasing but do have their drawbacks. It's best if these products are at least a year old. If they aren't, you may see problems with toxins or acids that are harmful to young plants. Of course, don't use any chemically treated wood.

Bark is sold as chunks, nuggets or shredded. This is the mulch you will see most often and is one of the most attractive as well as the most expensive. Pine, cedar, cypress (more on that later) and eucalyptus is available. It looks good and helps retain moisture and hold down weeds. It can be purchased in bulk or bagged (more expensive but easier to handle). The nuggets will last for years, but do lose their color quickly.

Pine needles are sold in bales, which makes them relatively easy to transport and apply. They are long-lasting. If you have friends with pine trees you may be able to talk them out of a few bags if you volunteer to rake them up.

Topsoil or compost, sold in bags at the garden center, can also be used. These products are generally thought of as soil amendments and may be used in conjunction with other more attractive mulches, such as bark.

Inorganic mulches are man-made and long-lasting. Although they generally work well at retaining moisture and reducing weeds, they offer nothing back to the soil.

Plastic does not seem to be used as much as it used to be, which is probably a good thing. It is a great weed barrier, but also blocks all moisture. You must have irrigation under the plastic or hand water. You also need to be aware it can get too hot under the plastic and retain too much moisture. Plastic is well-suited for a walkway where you will place another mulch on top of it, such as stones or bricks.

Bricks or stones can offer a neat appearance but may not be suitable for every landscape. Bricks are usually placed in walkways, while stones can also be used in beds. These materials can reflect heat back up to the plants so may not be appropriate in all situations. Also be aware that stones can end up in the grass and may become a projectile when hit with the lawn mower.

Landscape fabric is purchased in rolls and can be cut into any shape. It does "breathe," so it allows both air and moisture to pass through the fabric. It will cut down on weeds, but seeds can still germinate when they land on the fabric. Remove them early as the roots can get enmeshed in the fabric and become very hard to remove. This material is best covered with stones or an organic mulch for a more finished look.

At the beginning of the column I mentioned an article about mulch I recently read. It didn't cover new material but did remind me why I no longer use cypress mulch in my yard. Cypress trees, obviously, are harvested to make cypress mulch. These trees are not farmed for this purpose. They are naturally occurring trees. That means their numbers are dwindling because of this harvesting.

The issue gets complicated because harvesting cypress trees provides income for some Florida families and there are politics involved. I just keep it simple for myself and don't use cypress mulch. If you would like to educate yourself on the topic so you can make an informed decision, visit the Web site of the Gulf Restoration Network at healthygulf.org.