Dr. Carl Whitcomb is the president of Lacebark Inc., Stillwater, Oklahoma. He is a consultant, author, lecturer and researcher. For more info go to lacebarkinc.com.

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Northern Crapemyrtle
by Dr. Carl Whitcomb       #Trees

Dynamite® crapemyrtle

As I skimmed through some of the State-by-State Gardening Midwest magazines, it occurred to me that readers in Northern states, for example in Zones 6 and 5 and in even especially warm spots in Zone 4, can, if done properly, grow crepemyrtle (Lagerstroemia indica). I have a test plot in Ft. Atkinson, Wis., and have had crapemyrtle surviving, growing and flowering the last three years. The first year the plants grew but did not bloom. They are located on the south side of a wooden deck, which is on the south side of a sizeable house, but it is definitely a warm spot in the overall landscape. The last three years, about late July or early August, the plants flowered profusely until late September when cool weather shuts them down. This amounts to six to eight weeks of flowers with little maintenance.

Crapemyrtle, Lagerstroemia indica, cultivars have long been acknowledged as a major contributor of summer color in the South. Crapemyrtle in full bloom rival the flower show of any other landscape plant. Cultivars range in size from only 3 to 4 feet tall to tree forms, to 20 feet or more. Some cultivars have brilliant fall foliage colors and the new ‘Whit’ cultivars have dramatic wine, wine-red or purple new growth, adding significant color before the blooms.

But, crapemyrtle are typically considered cold hardy only in Zones 7 and higher. With a gradual cool down in fall, tops can survive 0 to minus 5 F. When winter arrives early and abruptly, tops may be damaged at temperature in the 20s F. When severe temperatures damage tops, all is not lost because the roots remain undamaged and when the soil warms in spring, the plants make a rapid recovery. Of the eight ‘Whit’ cultivars, Pink Velour® appears to be most tolerant to cold and requires the least amount of heat to trigger flowering in summer, but Dynamite® is only a few steps behind.

But, crapemyrtle have a desirable attribute shared by only a few other woody plants — they flower on new growth. In addition, new cultivars such as Red Rocket®, Pink Velour®, Burgundy Cotton® and Rhapsody in Pink® have spectacular red-wine or purple new foliage. As a result, even in Midwest areas such as Zones 6 and mid- portions of Zone 5, an early summer foliage show and mid- to late-summer flower show can be dramatic.

Even the new foliage of crapemyrtle can add color to a landscape. This is Burgundy Cotton®’s new growth.

In Northern areas, treat crapemyrtle as a hardy perennial and follow these steps:

• Locate crapemyrtle in full sun. A hot location gives best results.

• Plant crapemyrtle in the heat of summer when soil is warmest and root establishment is rapid. Do not plant late in the season after the soil has cooled. Getting the plant well established is key to survival.

• After a few hard freezes in the fall, remove all stems a few inches above the soil line; place a disc of ground cover fabric at least 5 feet in diameter over the area and mulch. In more severe climates, heavier mulch is beneficial. Mulch before soil freezes to keep the root-crown area warmer.

• In spring, as soon as all chance of frost has passed, remove mulch and fabric and allow soil to warm. Do not mulch during the growing season as bare soil heats faster than soil under mulch.

• After a few seasons, instead of three to five stems, 10 or more may emerge. In this case, more is not better. Select the strongest five to eight stems and remove the others. This provides larger flower clusters and a greater flower show.

• Crapemyrtle like it hot, so a location with reflected heat and light is desirable for this plant.

• Almost any soil will do, but keep in mind flowering is on new growth, so more growth typically equals more flowers.

• In most of Zone 6, flowering typically begins late July but not until early August further north.

• Fertilize crapemyrtle moderately to heavily once in spring, but not in fall.

• Water during dry periods, but crapemyrtle are tough and will survive even when neglected.

This not-yet-named crapemyrtle seedling was planted in a yard in Ft. Atkinson, Wis.
It is responding well so far, even after surviving minus 22 F in the winter.

Currently successful plantings of these new ‘Whit’ crapemyrtle are located in such diverse locations as Kansas City, Kan., Chicago, Philadelphia and Newport, R.I. Many climate and cultural factors are involved in tolerance of crapemyrtle to cold; therefore, precise performance predictions cannot be assured. However, testimonials from nurserymen, landscapers and gardeners as well as personal observations prompted me to share this information. As one nurseryman in northern Maryland said to me, “Two large Dynamite® in front of our office survived the roughest winter we have had in years, no dieback at all, while other cultivars were severely damaged or killed to the ground. You need to promote this plant more.”


(Photos courtesy of Andy Whitcomb.)


Posted: 04/23/12   RSS | Print


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