Good Rhododendron Mulches

A mulch of pine needles provides an airy blanket that conserves moisture, retards weeds, and provides nutrients to the rhododendrons. These needles are from an eastern white pine (left in picture).  

Many people spend a great deal of time watering, fertilizing, and weeding their rhododendrons. There is a much easier way, and it is healthier for the plants--natural mulch. In The Anderson Garden, we don't use any fertilizer, don't water established plants, and do a minimum of weeding. While it is not possible to totally avoid these chores in all climates and soils, the tasks can be greatly reduced.

Mulch is also good for the environment. Besides saving water resources and eliminating the need for chemical fertilizers and herbicides, it reduces runoff and acts as a first filter for the ground water. Mulch allows the gardener to make good use of a resource many people either burn or send to the landfill.

Not all mulches are the same. While purchased products, such as ground bark, will do the job, a much easier, cheaper, and more effective way to mulch is to plant the right companion trees for rhododendrons. But careful selection is important.

Many trees have invasive roots that rob shrubs of moisture and nutrients, defeating the purpose of the mulch they produce. And many trees produce a heavy mat of leaves or needles that solidifies as it dries. These same trees often create a canopy that is too dense for open shade loving rhododnedrons.

The best companion trees we have found are pines (above) and oaks (below). Both send down deep tap roots rather than spreading surface roots. We have rhododnedrons that have completely encircled pines and oaks as they have grown over the years, while firs and maples have killed a circle of plants around them (even grass.) These deep roots also absorb trace minerals from deep within the subsoil, and then deposit them on the surface in their leaves and needles. Oaks have the additional benefit of adding tannin to the soil around the acid-loving rhododendrons.

Pines and oaks provide a good filtered shade, especially if the lower branches are removed. They offer protection from the wind, but allow free circulation of air to reduce the threat of powery mildew. The mulch they annually provide is loose, letting air and moisture to penetrate, but blocking out light and and moderating ground temperature. (Sometimes you might need to plant trees that are not ideal rhododendron companions if there are overriding reasons. We planted several Douglas firs as a break against the notorious Enumclaw east wind, and a number of Japanese maples because their colors and shapes complement the other plants so well. Other competitive trees are single specimems, such as dawn redwood, sequoia, and sweet gum. They produce acceptabale mulch, but need plenty of space around them.)

 Oak leaves provide the same benefits as pine needes, and add acid to the soil. Some also have beautiful fall color.

Another good source of mulch is pruning. Everything we prune under two inches becomes mulch for the beds. Rhododendron trimmings are especially valuable, because they can return much of the potassium back to the roots of these potassium-hungry plants. But prunings from trees, hedges, fruit and berry stock, all have something to add to the soil.

We had a shredder but got rid of it. It is almost as fast to clip the pieces into six to eight inch lengths at the same time you are pruning, and the plants like the coarser mulch. It probably is just as fast if you consider the time for buying gas, replacing belts, sharpening blades, and doing other upkeep on these high maintenance machines. Equally important, they are so loud they prevent your neighbors from enjoying their gardens while you are shredding away.

Mulch makes for a win-win-win situation. It makes life easier for the gardener, benefits the environment, and keeps the rhododendrons happy.