HG: Homegrown Column April 11, 2009

PLANT OF THE WEEK: Minerva Rose Of Sharon, Hibiscus syriacus “Minerva” - This lovely shrub is covered in showy, large single lavender-pink flowers that have a dramatic reddish-purple center from mid-summer into the fall. Its ruffled petals give it a very fresh look. Minerva Rose of Sharon can grow 8 to 12 feet tall in an upright to rounded shape, and provides stunning color during the summer months. It is hardy to minus 15 degrees. BESS WYNN/Bookcliff Gardens

Need your advice on my Rose of Sharon. I’m thinking of transplanting it because it is about 4 feet from an outside door, and I’m concerned it’s going to get too big. It is 9 years old and about 5 feet tall and 3 feet wide.
Can I control its size by cutting it back? What is your advice for normal pruning of a Rose of Sharon in the spring? Thanks so much for always helpful answers and advice.
— Marla

Most people let their Rose of Sharon just grow. Left to itself, it will form an attractive rounded to upright vase-shaped shrub that will get 8 to 15 feet tall.

The size and shape are determined a bit by the variety and where it’s growing.

I have some 22-year-old plants in my yard that are a good 15 or 16 feet tall. These are a variety called Ardens that has small double lavender pink flowers and tends to grow in that upright vase shape.

They’re also crowded into a full shrub bed so they’re probably a bit taller than one planted out on its own since they can’t grow as wide as they could.

Other varieties (especially the single-flowered varieties such as Aphrodite and Minerva) tend to grow in a more rounded shape, not getting quite as tall but spreading wider.

Letting it grow isn’t much of an option for you, considering the space constraints you have, but you can prune it .

Since it blooms on current season’s growth, you can cut it back pretty hard every year to keep it shorter while preserving its flowering during summer.

The time to prune is early in the spring, anytime during the month of March is what I usually recommend, but you still have time if you get on it.

I’d cut it back 2 or 3 feet off of the ground. Going farther could be a bit risky.

I’d look at removing or reducing the oldest, thickest stems in favor of younger, more vigorous ones. Cutting them back this far every year should enable you to keep the plant in the 4- to 5-feet-tall range indefinitely.

When you prune, selectively cut back individual shoots so that you end up with an oval or rounded shape. By doing this, you can modify the growth habit of the plant (make an upright growing variety more rounded or vice a versa). This also results in a more natural-looking plant.

Plan on having this done every spring to keep the plant to the size you want.

We just added the silt from our irrigation ditch into our raised planters. Also, we have added some compost to them. How much should we add or will this even work?
Thank you.
— Linda

Actually, that “silt” isn’t bad soil to begin with. The texture is usually pretty good and there’s a good amount of organic matter in it.

Occasionally, this soil has a lot of clay in it, which isn’t all that helpful.

OK, here’s a quick lesson in soil science. The mineral part of soil is made up of three different particles: sand, silt and clay.

The difference between them is simply size. Sand is the coarsest, clay the finest and silt in between.

They all have their benefits and problems and a “ideal” or “loam” soil has some of all three in it

Our native soils tend toward clays, which make them poor at draining and poorly aerated. The sediment in the bottom of the ditch is usually sandy and/or silty since the clay tends to wash away in the water.

You can get an idea what’s in that sediment by moistening it to make mud and rubbing it between your thumb and fingers.

If it’s gritty, there’s a good amount of sand in it (that’s good).

If it’s smooth and “buttery” there’s a good amount of silt in it (also good).

But if it’s sticky, then it’s clay, and you’ll need to add more compost to the soil.

If you’ve already added some compost to the sediment, then you’re probably ready to go. I generally like to add one part organic matter by volume to two or three parts soil.

If the sediment seems heavy with clay, you may consider even going one part organic to one part soil to lighten it up.

Dennis Hill is the nursery manager at Bookcliff Gardens, online at http://www.bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or e-mail info@


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