Rhododendrons are light feeders. The main problem they have is competing for moisture. The critical area is inside the drip zone of each fir tree. So the area depends upon the size of the trees. Their roots extend out to and beyond their drip zone. I would not fertilize more than once each spring and then just use a good rhododendron fertilizer like Hollytone and at half the rate on the package. Too much nitrogen will prevent them from blooming.

I would go around each rhododendron bed with a mattock to cut any tree roots on the surface that are going into the beds. You only need to go down about 6 or 8 inches.

Thanks Rhodyman:

Okay, no more fertilizer for this year. Haven`t been able to buy hollytone here in Canada, will keep looking. And will continue to give my rhodies lots of water-then we shall see what next year brings.. For your info, many of the Firs are 50 plus years of age. Have a nice summer...

Sonny,

Be careful with too much moisture. They need a well drained soil. If they look wilted in the morning, then be sure to water. If they look wilted in the heat of the day but look good in the morning, then don't worry. Wet roots in the summer can lead to root rot which is fatal. Moist is OK, wet is bad.

Lots of places grow rhododendron under Doug Fir. The rhody garden in Eugene, Oregon, Crystal Springs in Portland, and just about any other rhody garden in the Pacific Northwest have a canopy of Doug Firs. I think if you are careful you will be OK. One thing is for sure, not much rain water gets under the canopy unless you have a lot of wind or run-off.

I got decent blooms this year after 1 fall application of sulfur and a spring application of Hollytone.

Then just to make sure I lopped off a branch in about April to try to shock it into flowering. Something worked, because I had more blooms than I've had. They are dark burgundy and just wonderful.

And believe me, rhododendrons are the trickiest thing I've attempted, LOL.

Laurabs,

Nothing you did this year such as removing a branch in April made any difference, except removing the banch removed some blooms. The buds for this years flowers were formed by the previous August. They set new flower buds after they finish blooming. By late August, most flower buds have been formed for the following season. Rhodies are like people, they need to reach puberty and that takes time. Also they need good nutrition, at least 2 hours of sun, and the correct acidity. They are light feeders. An application of fertilizer once each spring at half the recommended rate is more than enough.

FYI: Espoma does not sell their products in Canada at this time. They are hard to find even here in the Dallas area. While you could try to locate a mail-order company that will ship to you, I would use cottonseed meal instead, available in organic minded stores and cattle feed stores.

Best to sample your soil and have it tested by a soils lab before fertilizing.