by Ken Gibson - March 2000
This was the question put to a panel at a convention of the American Rhododendron Society held in Richmond at least ten years ago. The consensus of the five person panel was too much water. Since that time I have been lifting plants higher and higher and I have a 45° degree slope in some places on my hill. "Rhododendrons require drainage"; "Rhododendrons donít like wet feet". But it is my opinion that the best word is "SHARP" drainage. As I sit here and watch torrents of March rain water fall on my hill, already soaked from 100 inches in the last six months, I canít help think of those less fortunate with flat ground. At least I donít have puddles.
Soil breaks down to loam, from falling leaves and rain. It soon turns to muck or mud with no cavities for the mould which the roots require. The roots cease to live, and they can develop root rot in the summer heat. Death appears in 50 years or less..
The answer is in how high they are, in my opinion. I never plant rhododendrons, I place them. But first I wash away any mud with a garden hose at high pressure. Many times I will use a 3 inch bed of "hydro chips" or "cedar sawdust" to start with. Compost covers the exposed roots. The final root collar may be 16 to 18 inches higher than the regular ground level. This may be difficult if the plant is small, but the objective should be the same. The corners of the root pad can be stepped on or pounded down using a 4" x 4" timber as a ram. Now, hydro chips and needles can be placed on the sloping sides. Make sure that there is no clay-like dirt on the root collar. It may be necessary to secure or brace the plant for a year or two. I use black electrical wire and 8" sections of an old garden hose to secure, going from the base of neighbouring plants to a solid stem as high as possible. It is important the plant doesnít rock in the wind. I like to give the transplanted prize a sprinkle of "bone meal " or "canola meal" to promote roots. `Mary Grieg used to say "a happy rhodo is one that has just been moved".
To test your soil for drainage, dig a small hole say 12" deep by 18" wide and pour in five gallons of water. It should all disappear within five minutes. Another test is to make a large snowball of your soil, pack it firm and set it on a flat surface. If it stays together poke it with your finger as it should fall apart if you have the proper growing medium.
The soil changes a lot in 40 years of domestic use. The amount of shade is far greater and air circulation is far less. Look for old rhodos or Ďsurvivorsí in old places. The healthiest are planted up high. There are fine examples of this at Bamfield and Ucluelet. After 40 years on this hill that once turned to dust, I have a continuous battle with too much moisture or just plain drowning my plants. I have cut ditches up and down my hill creating valleys and used truckloads of cedar sawdust to soak up the mud and fill these riverettes. I am sure, in some areas I have a sawdust/mud ratio of three to one. In several areas, I now see the fruits of my labour. My only regret is I didnít get on with plant posture and lifting sooner, or better still, I wish I had started with 6" of coarse sawdust under everything. I am now using 23-3-23 fertilizer (slow release) March - April - May - five weeks apart and water only when a plant shows me it is thirsty by drooping.
The thoughts expressed above could be applicable to areas having perhaps 80 inches or more rainfall per year.