JARS v64n3 - Caring for Small Rhododendrons

Caring for Small Rhododendrons
Joe Bruso
Hopkinton, Massachusetts

This is a guide for caring for small rhododendrons. In the United States, the two predominant methods of propagating hybrid rhododendrons are by rooting cuttings and by tissue culture. The plants produced from these two methods need special care their first one to two years in order to have a high success rate.

How to Kill your Small Plants

Dig a hole in the landscape, plant them, water them once, and then forget them. Alternately, leave them in their pots in full sun and forget to water, or over-fertilize them.

Proper care can be divided into two timeframes: First summer and first winter

1. First Summer

Key to Success : Prevent desiccation!

The soil around your plants should be kept moist at all times. Letting it dry out completely is the surest way to kill them. This is especially true of plants grown in a medium with a high percentage of peat, since once peat dries out completely, it becomes very difficult to re-wet short of soaking in a bucket of water.

The two most common ways to prevent desiccation are to keep the plants in pots and water daily or as needed, or plant them in a "nursery." A nursery is a prepared bed with amended soil, at least partial shade, no tree root competition, and with the plants relatively close together. Average sized rooted cuttings can be planted a foot or so apart. This simplifies care, especially watering. The nursery should be watered every two days or so at first, gradually decreasing the frequency as the plants become established and/or as weather dictates. Rhododendrons can be kept in such a nursery for two to four years before they crowd each other and need to be moved.

When kept in pots or in a nursery for the summer, they should be located in a partly to mostly shaded location. The north side of a structure is an excellent location. High shade from oak or pine trees is also great. If they must be exposed to direct sun, early morning sun (as on the east side of a structure) is preferable to noontime and evening sun. The more sun your plants get, the more often they will need to be watered. Avoid deep shade, as found in a dense grove of white pines with low hanging branches.

2. First Winter

Key to Success : Protect from extremes of winter temperature, sun and wind!

A commonly used practice in colder weather areas is to build a simple plywood box to cover the plants. It can be small enough to cover one plant up to the dimensions of an entire sheet of plywood or larger, depending on how many plants you have. Construction with screws will make taking it apart easier. The box needs no bottom. Potted plants are placed as close together as possible on the ground inside the box. Mid-November is the usual time of year for this. The pots need to be well watered before covering. Put a mouse trap or some rodent bait inside the box to guard against mice and vole damage. A slight gap (one cm or a fraction of an inch) should be left on one area of the top to provide minimal ventilation. Bank woodchips or bark mulch around the base of the box to cover any gaps between the wood and the ground. If you have planted your plants in a nursery, the box can be built or placed over the nursery.

After their first protected winter, your small rhododendrons will be much more able to withstand the rigors of winter without special protection. Protecting them as described above for another year will still be beneficial, however. After their first or second year of protection, they can be handled in one of several ways:

1. Re-potted and grown on in larger pots for another year,
2. Planted in a nursery, or

3. If large enough, planted into the landscape.

Re-Potting Considerations

Small rhododendrons are usually started in an "artificial" medium - one composed of peat and Perlite for example. Rhododendron roots can be slow to grow out of a medium they are used to and into a much different medium. When repotting into larger pots, one should include in the new soil some of the ingredients found in the medium the plant was grown in (i.e., peat and Perlite) mixed with soil from their future nursery or planting location.

The pot should be large enough to easily contain the root ball plus allow you to add new soil all the way around the plant. Avoid pots that are too small for the root ball such that you have to jam the roots in with little room to add new soil. Alternately, avoid oversized pots in proportion to the root ball. Pull the roots apart as much as possible when either repotting or planting into a nursery or the landscape to help the roots to spread out into the new soil. Little to no fertilizer is required at this time. Better to err on the stingy side than over fertilizing, which can be lethal. A small amount of slow release fertilizer works well.

Summary

The keys to success with small rhododendron plants are very simple: keep them regularly watered at all times, and provide them with some protection their first winter. With just a little care you will be very successful.

Joe Bruso is a member of the Massachusetts ARS Chapter.