Early December along the Gulf Coast, and we haven’t had any serious frosts or freezes yet. But cold weather will be here soon! It is time to mulch those hibiscus, if not already done. Mulch basically acts as a blanket to hold in heat from the ground, keeping roots from freezing.
Put a little thought into choosing an appropriate mulch for your garden. With a record El Nino in the Pacific, many weather forecasters are predicting a very wet winter along the Texas coast, so good drainage is essential. Keep in mind that hibiscus do not like wet feet!
When choosing mulch for hibiscus, consider using a type that drains well. (My personal choice is a fairly coarse pine bark mulch.) Some of the fine shredded bark types can form dense mats after awhile, becoming soggy and promoting growth of mildew. The insulating value of mulch is primarily due to the air pockets trapped between the particles of mulch, so tightly packed material is not as effective in keeping plant roots warm.
If plants still have mulch from previous years, it is a good idea to rake it or otherwise loosen it up before adding more on top. Turn a little of your old much with a shovel or rake and look for mildew. If you see large areas of mold or mildew under the mulch, remove it and replace with a more coarse mulch to improve drainage and let a little air down to the roots.
Unless badly mildewed or infested with insects, old mulch can be left around the plants. It will eventually decompose and improve the soil. If you mulch heavily, add a little bit extra nitrogen fertilizer in the Spring, as decomposing organic matter actually uses up some of the existing nitrogen in the soil.
A good mulch application is about 4 to 6 inches inches or more in depth, extending out from the trunk as far as the branches reach. That is approximately the farthest that roots will grow from the base of the plant.
Mulch can only protect plant roots and perhaps a few inches of the plant stem. To protect the main stem and branches from freezing, covers or external heat is necessary. Another article..