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Keep those Rhododendrons blooming with these tips

Master Gardener Ciscoe Morris shares how to prune and feed for max blooms. #newdaynw

SEATTLE — Rhododendrons 101 by Ciscoe Morris:

Rhododendrons are among the most beautiful of all shrubs when it comes to providing spring blooms in Pacific Northwest gardens. There are, however, a few things to keep in mind when you plant and care for them in the pacific Northwest to make sure they live long and provide beautiful flower in your garden for years to come.

When you plant a rhody about half of the planting medium should be organic material. Compost or other organic material should be worked into the soil. Adding a large amount of organic matter such as compost will raise the bed, which will improve the drainage and aeration of the soil. Inorganic materials that may also be added to soil include perlite, vermiculite or small diameter lava rock.

The best time to move a Rhododendron is in spring or fall when conditions are cool and moist. They move easily, even when in full-bloom, but never try to move one when it’s putting out new spring growth. They’re easy to move without harming them; however big old rhodies can be incredibly heavy, so if you’ve got to move a honker, invite your strongest friends over by enticing them with the promise of a brussels sprouts casserole. 

Begin by digging a wide trench around the shallow, tightly knit roots. Next dig underneath the plant while rocking it from side to side until the rootball breaks free. Now dig a gradual slope on one side of the trench and lay a big piece of plywood on the incline. Place a blanket around the rootball, and station your buffest friends on each end to use it to pull the rootball up the board and out of the hole. Now if you can figure out a way to move the beast across the garden, it’s ready to go into its new home. One last bit of advice: Don’t feed your helpers until the work is done!

Mid-April is a great time to fertilize spring blooming acid-loving shrubs such as Rhododendron, and Azaleas. These plants put on new growth soon after the flowers fade in spring, so an April feeding with a balanced fertilizer will promote increased growth, which normally leads to increased flowering the following year. It’s best to use organic fertilizers formulated for acid loving flowering shrubs (available at local nurseries) when feeding Rhododendrons. Rhododendrons are shallow rooted. The nutrients in synthetic fertilizers are immediately available to the plant. If the fertilizer is over applied or if conditions aren’t quite right for nutrient uptake, the salts in the fertilizer can easily burn the roots of the plant. The nutrients in organic fertilizers, on the other hand, are available to the plant only after microorganisms in the soil act on them. This is a natural slow process that doesn’t create salt build-up, thereby not burning the roots. The end result is even, adequate growth and better flowering.

The best time to prune your Rhododendron is in the spring right after the flowers fade. Soon afterwards new growth will emerge, and by early summer flower buds will form at the end of newly grown branches. If you wait too long, pruning can interfere with the budding process and reduce the number of blossoms you’ll get to enjoy next spring. By the way, It happens to all of us. We fall in love with a spectacular flowering Rhododendron at the nursery; then plant it right in front of our picture window so we can look out to admire the attractive blooms. The problem is that many Rhododendrons are actually trees and may reach 20 feet or more. Before we know it, the plant totally blocks the view out the window. Most folks solve the problem by cutting their rhododendron down close to the ground. This works because rhodies have special buds and will branch out practically anywhere you cut them. The problem is that after such a hard pruning, it can take 2 or 3 years before a rhody will begin blooming again, and by then, the plant’s inevitably grown back to block the view once more. Rather than whacking your rhody down every few years, consider removing the twigs and foliage from the lower portion blocking the view, while allowing the canopy to grow up and remain above the window. Many rhodies have attractive exfoliating bark and interesting branching patterns. Within a few years, you’ll be able to look out through the magnificent trunks while enjoying a canopy filled with blooming flowers above the window.

It's is not necessary to deadhead Rhododendrons to get flowers the following year, so if it’s a dangerous climb up a rickety ladder, you don’t really need to do it. However, you get more branching (and therefore many more flowers) if you remove the spent flower clusters soon after flowering is finished. Also, there is no doubt that rhodies look better if the spent flowers are removed, so if it’s not a 15ft monster it’s probably worth the effort. The old flower trusses snap right off, but take care not to injure the new buds at the base of the spent flowers in the process.

Finally, there are too many ultra cool rhodies to list all of my favorites, but here are a few of my favs.

Rhododendron spinuliferum (Firecracker Rhododendron) is a true oddball. The flowers are so unusual, they really do look like firecrackers. I like it because it's cool looking and I'm crazy for unusual plants.

R. King George Loderi has spectacular bark, and super fragrant big white flowers.

yakushimanum is native to the mountainous areas of the Island of Yakushima. This shrub provides year-round interest with its thick, glossy and leathery, curled leaves with velvety brown hairs on the undersurface. New growth is covered in dense white hairs. Attractive dark-pink buds open to light-pink flowers that fade to white in mid-spring. 

Rhododendron oreotrephes is a real favorite of mine and among the most easily grown species in cultivation. Bright blue-green new leaves and pink to rose or purple flowers in mid to late spring. It's self cleaning and does not need to be dead-headed. Best in light shade.

Segment Producer Suzie Wiley. Watch New Day Northwest at 11 a.m. weekdays on KING 5 and streaming live on KING5.com. Contact New Day. 

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