Raleigh Landscaping and Mulch Basics - From the Ground up
Nature abhors a vacuum. She pretty much doesn't tolerate bare earth, at least not for very long, so if you eradicate weeds in any way something else has to take their place. Of course, maintaining five or more dogs might create a bit of a moonscape effect if that's what you're looking for, but under most circumstances she'll put something there if you don't. She's likely to cook up a plan of her own to occupy that prime piece of real estate, usually involving more weeds.
The winning plan of attack is to get rid of weeds and weed roots on your Raleigh lawn immediately prior to putting down a solid layer of gravel or mulch. Merely covering up the persistent types like Bermuda grass or nutsedge will not stop them from growing. It might temporarily slow them down a bit, but it won't stop them.
Your new mulch layer will in some measure control weed growth, but please know that it will also prevent your treasured plants from re-seeding themselves for precisely the same reason: too much dense matter on the ground to allow an aspiring young seed to come in direct contact with the soil. Vegetables known to "volunteer" a new offspring somewhere near last year's vegetable bed are likely to go out on strike permanently, and biennials may also disappear entirely before their second scheduled appearance.
On the plus side, when winter rolls around in Raleigh, the soil underneath the mulch will not be susceptible to winter's freeze-and-thaw cycles, and a protective mulch layer will prevent perennials from "heaving out," as they say, during a thaw period, soon to be zapped hideously during a freeze period. Basically the mulch tends to regulate the temperature of the ground underneath it to keep it on an even keel.
For this reason you should mulch as much of the root zone as possible. This is easy to estimate for petunias but not so obvious for a Leyland Cypress, both common in Raleigh landscapes. The general rule is to extend the mulched area three to six feet from the base of a large plant while avoiding, if at all possible, piling it on against the plant's base. Start an inch or two away from the plant to prevent bark decay.
For the same reason, it's a real bad idea to lay a whole bunch of mulch up against your house, particularly any wooden parts of your house. Mulch does have a few drawbacks and being a natural material with a certain tendency to decompose is one of them. Letting mulch come in contact with any wooden structure that you hope will remain standing can cause good old-fashioned wood rot or the more exotic development of Meruliporia incrassate, which translates roughly as "house-eating fungus."
The depth of your mulch bed depends on a variety of factors, including the type of mulch you're using and the drainage and moisture conditions of your soil. Sandy soils, like those found in Eastern North Carolina, dry out quickly and should get an extra heaping helping, at least three to four inches. Swampy areas, which are not as common in Raleigh, Cary and Chapel Hill, probably shouldn't be mulched at all. For areas surrounding a plant that requires good drainage and doesn't like to have its feet chronically wet, you might try something else that doesn't hold moisture quite so well, such as pea gravel or coarse sand. Also, never mulch over the crowns of perennials as part of your fall garden clean-up ritual.
Let's say for purposes of calculating quantity that you want to mulch a 100-square-foot area of your Raleigh yard. For a six-inch depth, look to buy at least two cubic yards. A four-inch depth requires 35 cubic feet, a three-inch depth takes one cubic yard, and a two-inch depth needs 18 cubic feet, and a one-inch depth calls for nine cubic feet. For an annual or biannual replenishmentódepending on the type of mulch you buy and its rate of decompositionóthink in terms of laying down a one-inch top layer every year.
The best time in Raleigh to mulch is in the spring after the ground has warmed up a bit, but there are almost no bad times. Mulching in the early spring before the ground warms might arguably retain the cold and delay a plant's growth, but it's not likely to kill anything. A lot of gardeners feel like they're stretching some sort of comforting blanket over their little green friends when they put down a fresh layer in the fall.