Keeping your rhododendrons protected is important. The highest recommendation for such protection is through mulching. Not only does this provide the nutrients and acid levels that rhododendrons need, but this also gives them warmth, root “conditioning” (meaning, it keeps the roots cool when it’s too hot outside) and also sun protection. On the other hand, mulching your rhododendron helps keep the roots from freezing in the winter. Mulch in and of itself is a great insulator, and can be applied to rhododendrons in more ways than one.
The best mulch for a rhododendron is one using pine needles. Pine needles have a natural acidity in them and so can help to keep the soil’s pH level to about a 5.5; if you aren’t sure about the current pH level, you can get a soil test kit from your local gardening center.
When you mound your mulch around your rhododendron, you help protect the trunk from all sorts of parasites. However, if you were to create a funnel shape in the mound which would help filter water down into the root system of the plant, you can also give the rhododendron the chance to take in the acidity of the mulch. When you use a year-round mulch, it may be a good idea to blend your own pine needles into it just to make sure you have enough acidity going to the roots.
The rhododendron’s roots grow shallow and wide. The way they span out is kind of like a champagne or wine glass. The plant grows up, but the roots help to balance it with a wide bottom. For this reason, it’s important to spread a layer of mulch down and out, just like the roots go. When you water your rhododendron right over the mulch, the nutrients and acids in it will slowly trickle down with the water to the roots and soil, thus lending the acidity necessary to keep the rhododendron healthy.
When you prepare your rhododendron for the frigid temperatures of wintertime, mulch is a necessity. As mentioned before, mulch is a great insulator. It can help keep the roots from experiencing “winter burn,” a condition in which the roots freeze and the plant can’t get water and food from them. Even in the event of a snowfall and melt, the nutrients in your mulch are given to your rhododendron.
Keep in mind that when you mulch your plant for winter that you should keep the mulch about an inch away from the trunk of your rhododendron. This will make sure that any critters looking for a warm place to stay don’t decide to eat your plant as a mid-winter snack.
Remember that as you go through your different choices of mulch to check your soil pH first, because using acidic mulches may not be necessary. Just make sure there’s no alkalines in your mulch, which could harm the acidity of the soil. If you’re still in doubt, check with your local nursery. They can tell you exactly which mulch to use and, if necessary, show you how to apply it to your rhododendron.