Plant Rhododendrons Now
Rhododendrons are one of the most difficult ornamental plants to grow in landscapes. This year the rhododendrons did exceptionally well due to the cool, moist spring. Many growers noted that the ornamental plants bloomed heavier than normal and that their flowers lasted longer.
In their native habitat, rhododendrons grow in regions where the climate is cool, in soils that are well-drained but with ample moisture.
The hot, dry conditions frequent in our summers stress these plants. Add trying to grow rhododendrons in moderately to poorly drained soils, and many bushes are stressed to their limits.
If you want to guarantee success, plan to spend twice as much time and money in preparing the soil of the planting site as you do on purchasing the plants.
Rhododendrons should be planted only in well-drained soil, preferable a sandy loam. Test the soil because the desirable pH for growing rhododendrons is between 4.5 and 5.0. The soil also needs an abundant supply of calcium and magnesium. The best amendments to use to supply both of these elements are gypsum (calcium sulfate) and Epsom salts (magnesium sulfate). I recommend blending one-half cup of gypsum and one-quarter cup of Epsom salts in the soil.
Dig a planting hole in the shape of a basin with sloping sides and a rounded bottom. The depth of the hole should not exceed three-quarters the height of the root ball. The diameter of the planting hole should be four times larger than the diameter of the root ball.
If the rhododendron was grown in a container, remove the container and examine the roots. If the roots are matted around the outside edge of the root ball, cut into it with a sharp knife. Make four or five one-inch-deep cuts uniformly spaced around the root ball. The cutting of the circular roots will stimulate the roots to grow into the new planting soil.
If the plant was purchased balled and burlaped, the roots have already been cut. No further cutting is needed.
Do not use peat moss to amend the planting soil. Peat moss holds too much water and may contain the spores of the disease causing Phytophtora cinnamomi fungi.
Instead use an equal blend of pine fines and compost. Thoroughly mix the pine fine-compost blend with an equal amount of the existing topsoil. Pack the amended soil around the root ball including that portion above grade. Apply an inch of compost as mulch and irrigate thoroughly.
Irrigate the plant well two to three times a week until it becomes established and shows signs of new growth.