Timing Fertilizer /Pruning for Rhodys

lawnkid(Central NJ)March 13, 2007

I planted five different rhododendron shrubs last fall. These were Chionides (white flower), Catawbiense Grandiflorum (purple flower), Capistrano (yellow flower), Vulcan Flame (red flower) and Roseum Elegans (pink flower).

Spring is approaching and I would like to know when the best time to fertilize these plants is.

Also I am very interested in promoting flower production year after year while controlling growth by pruning. Ideally I would like to enjoy a crop of flower production each year, and immediately after blooming do the pruning to manage the growth. This obviously will require expertise on timing fertilization and pruning, and how to prune. I donÂt think I will be doing any mayor pruning since these were planted last year, but I still need to learn this information. They are currently 2 feet tall, and I would like to keep the plant size to no more than 5 feet.

I read that they should not be fertilized later than June for central NJ. If they are fertilized late the new growth will not get to mature to a bud before the cold weather arrives in the fall. Bud formation is what turns into a flower the following year.

I will greatly appreciate your advice.

Thank you

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rhodyman(SE PA, USDA Z6)

First the don't need fertilizing or pruning. They need good acidic soil and good drainage. They also need to be kept from drying out and from being wet.

If you do fertilize, fertilize with a good rhododendron fertilizer like Hollytone at half the rate on the package just before they bloom.

If you do prune, prune just after they bloom. I would only prune dead wood and any branch that is growing out of balance with the rest of the plant.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

    Bookmark   March 13, 2007 at 5:39PM
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morz8(Washington Coast Z8b)

Annual pruning of rhododendrons to keep them within a certain size range is never a good idea - buying a plant that will actually fit your site is better.

Having said that, I think roseum elegans is the only shrub in the 5 you mention that might possibly exceed 5' in 10 years.

If you wish for a more compact and dense form for your young shrubs, you can pinch (with your fingers) rather than prune, no tools required.

As growth begins in Spring you can pinch out the terminal leaf buds as they begin to elongate and unfurl. Do not mistake the round, fat, blunt-tipped flower buds for leaf buds.

This will force shoots (branching) to develop from dormant eyes in the lower leaf axils. A plant hormone is produced by the leaf buds which inhibits development of dormant buds along the stem. Flower buds do not produce this hormone. Continue this pinching procedure for two or three years - by then you should have well filled-out shrubs producing more flower buds than if they'd been left to their own growth habit.

    Bookmark   March 13, 2007 at 7:54PM
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