Q&A – Planting Rhodos in Forests

Q: Planting rhodos in a forested area: Dig in or mound on top? Plant mainly in mulch or mix in with soil?

Dr. Glen Jamieson says:
There are many rhododendron species and hybrids, with many demanding different microhabitat growing conditions for optimal growth and survival. Alpine species, such as many small-leaved lepidotes, naturally grow in highly exposed environments, with exposure to bright sunlight and moisture from clouds. They thus grow best in sunny locations that have good drainage, conditions not often met in a forested area.

Lepidote rhododendrons, those without scaly leaves, grow mostly at middle to higher Asian mountain levels, where forests often occur and so will do better in dappled light. All rhodos have shallow root systems, typically extending less than 30 cm (one foot) down, so they can either be planted in shallow holes or in a mound on top of the soil. In part this depends on the soil’s characteristics – on the Englishman River estuary, my substrate is mostly sand, so it’s easier for me to at least partially plant on top of the soil. I say partially, since I bury them slightly to give more wind resistance, as initially I had no vegetative windbreak in our windy yard.

Regardless, planting holes or mounds should be about twice the size of the root ball, and added soil mix media should be a mixture of substrate, such as 50% organic matter and 50% slightly sandy topsoil. They require well-aerated and drained soil that is high in organic matter. Rhododendrons are acid-loving plants, but this is not usually a problem on Vancouver Island. Good choices of organic materials are decomposing pine or fir needles, composted tree bark, chopped leaves, or a peat substitute. I recommend putting 7-10 cm (3-4 in) of bark mulch around planted rhodos, with a gap of about 5 cm away from the trunk.

Finally, planting around and under deciduous trees or Douglas-fir is fine, but be careful planting around cedars. They need more water, and will send their roots out a considerable distance to get it. This may make it hard to keep a rhodo planted near them with sufficient water, and they can easily shade out a rhodo too, as their thick canopy can block a lot of light.

 

Master Gardener Linda Derkach says:
In addition, I’d like to stress that members should do some research first before buying and planting to ensure that they have the cultural requirements necessary for success.

For instance, some small rhododendrons are epiphytic and will die if planted in our garden soil – even when amended.  They want to grow up in trees, etc.  So they may need to be in a big pot with highly friable medium.

I would also add that all rhododendrons need sunlight in order to set buds and bloom.  Planting among evergreen trees will limit the amount of bloom.

A good solution if you have evergreens is to position the rhododendron where it will get lots of morning sun and afternoon shade.  So the trees need to be on the west side of the rhododendrons to give them protection from the hot afternoon sun.

Given that more Heat Domes are likely, having afternoon shade is really important.

 

Rhodo expert Marilyn Dawson says:
To answer fully you really need to know what a forested area looks like. Coniferous or deciduous?  Dense shade or filtered light? Late day light or earlier? A grove of deciduous trees can provide dense shade when leafed out, but considerable light for the rest of the year; but perhaps not enough for some rhodos. That boils down to ‘know your rhodos, know what they require’.

Eg. I planted R. callimorphum once amongst a group of mixed deciduous trees, being told it needed filtered light (which it sort of got). It grew nicely, looked healthy, but never bloomed. In a last-minute move before I chucked it,  I replanted it in a slightly brighter area and it blooms beautifully every year. Knowing your plants and their general requirements, and knowing your soil and light conditions are essential.

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Please remember:  Gardening is part science, part art, part skill, and a large part luck.  Sometimes even if you do all the “right” things, a plant still won’t thrive.  We offer the best advice we can, but we can’t guarantee that your plant(s) will thrive… or even survive.  MARS assumes no liability for any damage that may occur to your plants, person, or property as a result of or coincidental to our advice.

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