It is a fairly easy process to transplant your rhododendrons, even if they are on the larger size. However, there are certain conditions about the new location that should be met, as well as a few basic transplanting steps, to make sure that your rhododendrons remain healthy and thriving.
Step 1 - Know When to Transplant
Rhododendrons can actually be planted just about any time of year outside of their soft growth cycle and the hottest of summers. However, for cool weather climates, it is recommended that they are planted in early spring so that the root system can become established before the summer heat sets in. Try transplanting dormant plants to reduce the shock of transplanting.
In warmer climates, it is best to transplant from late summer through the fall so that you avoid the hottest part of the summer (which is especially trying on top of the shock of transplanting). This way you still give the roots a chance to become established before your ground freezes over.
Step 2 - Prepare the Soil
This is probably the most important step in transplanting rhododendrons, as they are fairly picky about the soil they will grow in. They require a very well draining, porous, and acidic soil. If your soil pH is above 6, you can acidify your soil by adding agricultural sulfur or ferrous sulfate to it. Don’t use aluminum sulfate, as aluminum is harmful to the plants.
If your soil is too heavy, such as clay soil, you need to prepare a raised bed for your roots. If you don’t, even if you fill with porous soil, the surrounding heavy soil will act as a bucket and retain too much water for the roots. If necessary, plant high and either taper off the soil height or use a retaining wall. Adding organic mixture can help as well, even for loose, sandy soil.
Especially for hot climates, where root rot organisms thrive in warm, wet soil, mix in at least 50 percent of fine pine bark with your soil to promote better drainage.
Step 3 - Prepare Root Balls
If your root balls are dry, start by soaking them thoroughly in a tub of water before transplanting them. Even if they aren’t dry, hose off the root ball. You can leave any soil mixture around your root ball from prior planting or potting, but be sure to at least loosen the outer roots so the finer roots can establish themselves in the new soil.
If your rhododendrons are being transplanted from a container, you should loosen and even cut some of the outer roots. This will encourage new root growth once it is transplanted into the new soil.
Step 4 - Plant
When you dig out your hole, bear in mind that your rhododendrons have a shallow root system. Dig your hole wide, but no deeper than the height of the root ball so that the root ball is at the surface once covered. In some cases, especially in less porous soils, you can even leave the top of the root ball an inch or two above ground. Also, remember that they should never be planted deeper than they were grown.
When filling your hole back in, be sure to add some sort of organic mulch mix to the backfilled soil, if you haven’t already.