Hibiscus like warm days, even hot days, but they do not like scorching mid-summer heat. In the mid-day sun, leaves will wilt and blooms quickly shrivel, unless the plants have plenty of moisture and at least some shade. Mulching around hibiscus plants helps prevent soil from drying out quickly, and may keep the roots a little cooler.
Without mulch, hot sunny days rapidly dry the soil, stressing the plants. Then the gardener comes along, sees wilted leaves, and waters heavily. Much of that water may be wasted, through runoff or evaporation, and a continuing cycle of too-dry and too-wet is not good for the hibiscus plants. To avoid this, add two to four inches of mulch around your hibiscus plants. By insulating the soil from heat, wind, and sunlight, evaporation is greatly reduced.
Then, water just a little, every day. This keeps the plant roots cool, and at just the right degree of dampness for the hibiscus to thrive and bloom. Drip irrigation, with a timer, is one of the best methods of watering, and the drip tubing can be hidden under the mulch. Mulch should not be built up against the plant stem for more than an inch or so. The plant’s bark needs to breath, or rot may set in. So pile the mulch around the plant, covering the root area, but scoop away a little hollow all around the base of the actual plant. (This is true for most plants, and especially for large shrubs and trees.)
There are many types of mulch, ranging from fine shredded bark to very coarse bark chunks. Some companies are even making mulch products from shredded rubber tires and similar materials. ( editor’s note: Personally, I much prefer natural materials like bark, instead of rubber or plastic materials. Synthetic materials will eventually end up mixed into soil or spread over surrounding yard areas, and they will take many, many years to biodegrade into the soil.)
Natural bark mulch decomposes in a few years, and in the process improves the soil by adding nutrients and texture. Fine shredded mulch may compact into a tight mass, and large bark chunks may wash away too easily, or leave gaps that reduce the insulation value of the mulch. A medium size mixture seems to work best. Cedar much is a popular option, because it repels many insects, and will not biodegrade as rapidly as other woods, such as pine bark mulch. Although more expensive, in some cases cedar mulch may last as much as twice as long as pine mulch. Exposure to sunlight and water are the main factors in determining how long mulch will last.
Whatever type of mulch is used, it is a good idea to stir it up a bit, every few months. A gardening rake or hoe may be used to turn the mulch. This aerates the mulch, reducing the chances of mildew or fungus getting a start in dense matted areas.