Mulch is important throughout the year for shrubs, trees, and perennial beds—even if the plants are dormant. But what do you do with old mulch that had been left on top of annual flower beds or vegetable beds during the winter? The plants have died due to neglect or frost and the food crop has been harvested. Is the old mulch still viable? Should it be removed? Used again?
The present FAQ, by contrast, relates to empty beds (living plant material has either died or has been harvested), and the question focuses on the mulch: specifically, whether the old mulch is still viable—and, if so, what you should do with it. This pertains to the biodegradable material (bark, leaves, straw, etc.), not to mulches that do not break down readily (stone, plastic, etc.).
Is Old Mulch Still Good to Use?
Vegetable garden beds and annual flower beds will not have plants in them during the winter but are mulched in fall to protect their soil from the harsh elements in winter. You have worked hard to build up the fertility of your garden soil, so you would not want gusty winds or torrents of water carrying any of it off, would you? If the condition of the old mulch has not decomposed appreciably by the time spring comes, it will still be usable.
How to Determine If Old Mulch Can Be Reused
To determine its condition, scoop up some of the mulch in your hands. Has it more or less broken down into fine particles, so that it is no longer clearly distinguishable from dirt? In that case, it will no longer function very effectively as a mulch; it is time to replace it.
If, however, it has mostly retained the look and feel that it originally had, then you can re-use it. The one exception would be if your plants in this garden bed had experienced disease problems last year that you think can be traced back to the mulch, in which case you would want to remove and dispose of said mulch properly (check with the officials in your town to determine a proper way to dispose of such material).
How to Reuse Old Mulch
If upon inspection, you decide that the old mulch has not, in fact, decomposed appreciably, you should rake the old mulch aside for now so that you can prepare the planting bed. If you need to get it out of the way, shovel the mulch into a wheelbarrow, dumping successive loads onto a tarp off to the side. Apply compost onto the vegetable garden bed or annual flower bed, and till it under or work it into the soil with a spade.
Now you can see why the first instruction was to rake the old mulch aside: in the course of rototilling or spading the compost into the garden, the old mulch would have been tilled or spaded under, forcing you to acquire and apply new mulch. That would be a waste of time, energy, and money.
Now put the old mulch back onto the planting bed.