Tuesday, February 16, 2010

Plant Care Profile: Crape Myrtle (Lagerstroemia indica)

In many places where winters are mild enough for them to survive without protection, crape myrtles (Lagerstroemia indica) are among the most popular flowering shrubs or trees. I remember noticing this plant for the first time as a child on a summer vacation in the northern Italian region of South Tyrol. Crape myrtles are very common throughout much of southern Europe and the American South, where their frilly blossoms in colors ranging from deep red to white dominate both public plantings and private gardens for much of the summer. Beside the showy flowers, the plants is also appreciated for its unusual bark, which is mottled in various shades of brown and silvery grey. This feature is most notable in plants grown in areas where the absence of hard or prolonged frosts permits Lagerstroemia indica to grow into a sizable shrub or even a mid-sized tree with fairly thick trunks and branches. However, the plant can also be grown as a die-back shrub in far colder regions. In that case not much of a trunk with the characteristic bark is likely to develop but the gorgeous flowers still make this plant well worth the effort.
 
 A light pink specimen of Lagerstroemia indica in a south-facing border in my family's previous garden in Zone 6a suburban Michigan. At the time this picture was taken this plant had been growing in the garden for about three years. I originally brought it home from northern Florida, where I had bought it for $2.99 at a Walmart.
Origin: Despite its Latin name, Lagerstroemia indica is native primarily to East Asia, with a natural range including parts of China, Korea, and Japan.
USDA Hardiness Zone: According to most sources, Lagerstroemia indica is hardy to Zone 7b but in my own experience the plant is hardy at least to Zone 6a. However, in much of Zone 7 and in Zone 6 or any colder area, crape myrtles will be grown almost exclusively as die-back shrubs that resprout every year from the base, whereas in warmer areas they develop substantial trunks and can grow into sizable trees. Hardiness in also dependent on summer climate, since the new wood of this shrub needs heat to ripen well. Thus the more summer heat the plant receives the more cold it can generally withstand during the colder months. This past summer the Lowe's near my parents' house in Michigan was also selling crape myrtles of a low-growing variety with deep pink flowers which were tagged as being hardy to Zone 5. I am not sure to what extent that is true but they were on sale and seeing as a regular variety bought in Florida has done fine for us in Michigan for over five years now I decided to give them a try. I guess we will see next summer if they really survived the winter any better than normal varieties.
 A close-up of the flowers of the crape myrtle in my family's garden
Size: There is tremendous variation in crape myrtle size depending on the variety and the manner in which the plant is being grown. As a die-back shrub in cooler areas, Lagerstroemia indica will hardly exceed 6' (ca. 1.8m) but grown in warmer areas some varieties can reach heights of 25' (ca. 7.6m) and widths of 20' (ca. 6m).
 Crape myrtle flowers in my parents' garden just beginning to open
Flowering Time: Flowering time for crape myrtles depends a lot on the local climate. In vey warm areas the plants will begin flowering in early summer and continue flowering for a good month or more, in cooler areas they will begin flowering later. Grown as a die-back shrub resprouting from the root each spring, my specimen in southeastern Michigan usually begins blooming between mid-August and the beginning of September, depending on how hot the summer has been up to that point, and continues flowering until late September or early October.
Light Requirements: Lagerstroemia indica needs full sun - generally the more sun and heat the plant receives, the sooner it will flower and the hardier it becomes.

 Large specimens of Lagerstroemia indica in the park at the Florentinerberg in Baden-Baden, Germany (Zone 8a)
Soil Requirements: Crape myrtles appear to do just fine in a wide variety of normal garden soils ranging from sandy loam to clay, though in my experience they benefit a good deal from decent drainage, annual top dressings of compost and a good layer of leaf mulch.
Siting in the Garden: In areas that are warm enough - roughly Zone 7b and warmer - Lagerstroemia indica can be planted anywhere where it receives plenty of sun and its potentially sizable growth can be accomodated. Where winters are colder or summers are not very hot, care should be taken to plant this species in a very warm and sheltered spot, ideally in a border at the foot of a heat-retaining south-facing wall.
 Crape myrtles grown as standards in the park between the Sultan Ahmet or Blue Mosque and the Hagia Sophia, Istanbul, Turkey (Zone 8b-9a)
Care: Ideally, crape myrtles should be planted in spring so they have plenty of time to get established before the winter but in warmer areas this is not essential. Even my first crape myrtle in Michigan was planted in August since I had brought it back from a summer trip to the South and it ended up making it through the winter more or less ok, though it failed to flower the following summer. At the time of planting, plenty of compost and bone or blood meal should be incorporated into the soil to give the plant a good start, and afterwards the area around the plant should receive a good layer of leaf mulch or wood chips to preserve moisture and to prevent extreme fluctuations in soil temperature. In warm areas, not much care is required during the growing season in first or subsequent year, apart from moderate irrigation during times of drought. However, in colder regions plants will have to resprout from the base and reach flowering size within a single season beginning their second summer in the garden and for this reason they benefit greatly from a biweekly feeding with liquid fertilizer to speed growth along. One should stop fertilizing once flowers begin to appear in late summer so the wood can ripen properly for the winter. In late fall, plants grown in Zone 7 or colder should be given a heavy leaf mulch for winter protection. I like for the mulch to stand at least 1' (ca. 30cm) - the higher the better. For this one can simply pile up the leaves over the plant or one can build  a simple wire cage around the plant to keep the leaves together. The mulch can be left on the plants until mid-spring, when it should be removed very carefully so as not to damage any new sprouts that might already be emerging. They will be extremely pale due to the lack of light but will quickly begin to turn green or reddish-green once exposed to the sun. However, if the plant has not yet begun to resprout when the mulch is removed that is not necessary a reason for worry since Lagerstroemia indica can be extremely slow to leaf out in the spring. Give the plant at least a month before giving up on it or discarding it because might very well come back! In warm regions where the plant requires no special winter protection and grows into a large shrub or tree the main care to be undertaken in late winter is pruning, which is not necessary for the health of the plant can be carried out to keep it to a specific size or give it a desired shape. Since Lagerstroemia indica flowers on this year's wood, it can take a strong pruning and still flower well as long as thhe pruning is carried out in the dormant period. In much of southern Europe, crape myrtles are commonly pruned like osiers (Salix viminalis), whose flexible twigs are used for basket weaving: grown as a standard, the branches are cut back hard every winter to only a few inches/cm above the top of the main trunk, encouraging the plant to produce a head full of strong young shoots every year. The main pest problem that appears to affect Lagerstroemia indica consists of mildew and other fungal infections, though I have never had any problem with this in Michigan, and it does not appear to be too much of an issue in most warmer regions either. In general, good ventilation and plenty of sun appear to be the most important strategies in keeping such afflictions at bay. The one pest problem I have encountered in Michigan are Japanese beetles (Popillia japonica), which are very fond of the buds and flowers of this plant. In a domestic garden setting, I have found it the best strategy of defense to go around the garden collecting and destroying the beetles once or twice a day from the day when they first begin to appear. This might seem tedious but they are actually quite easy to collect off the plants since they are suprisingly slow, especially early in the day when it is still relatively cool. Besides, manual collection means that no other plants or beneficial organisms are harmed in the process. In the long run, the numbers of beetles will diminish drastically.
An old specimen of Lagerstroemia indica in the gardens of the Dolmabahçe Palace in Istanbul, Turkey (Zone 8b-9a)
Propagation: Crape myrtles can be propagated from seeds as well as from softwood cuttings taken in summer or hardwood cuttings taken in late fall. For softwood cuttings a rooting hormone might be used. By and large, however, relatively few home gardeners propagate Lagerstroemia indica themselves since it can be easily and relatively cheaply bought in most places.
 
A deep pink crape myrtle in the Katz'sche Garten in Gernsbach, Germany (Zone 8a)
Use in the Garden: Lagerstroemia indica is a beautiful, eye-catching flowering shrub or tree that will bring stunning late summer color to a sunny shrub border. Where the climate is warm enough, it can look wonderful as a large solitary shrub or tree surrounded by lawn or groundcovers, which highlights not only the plant's brightly colored flowers but also the pretty bark of its trunk and branches. In areas where the plant dies back to the ground in winter, it is best integrated into a sunny perennial border or a planting of relatively small shrubs not likely to overtake it while it is rebounding in spring and early summer.
Sources: http://www.ag.auburn.edu/hort/landscape/crapemyrtle2.htm
http://davesgarden.com/guides/pf/go/1/

12 comments:

  1. Ok-I'll try this in the back yard. I thought it was strange, last summer, that I hardly had any Japanese beetles, but now I know it was due to your diligence!

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  2. Well, there were so few last summer that I am pretty sure that there must have been summer other reason as well; I do think, though, that the regular collecting does make a difference, and it definitely reduces the damage the beetles cause.

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  3. I have just had a large (pale pink) tree planted in the Southern Hemisphere. It is therefore now close to the end of summer. It is approximately 3 m tall. Its growth has to adjust to its new position. Its transplant was obviously a shock to its system. Could you suggest any special care for the plant over the next year to get it started and settled and growing? Is it best to prune it or just leave it? I would like to encourage as much root and branch growth as possible at least until it is established. Any suggestions?

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  4. Hi Andrew,

    Sorry it took me so long to reply! I was traveling and had only very occasional internet access. As for the crape myrtle, I would wait to prune it until late spring since these plants can be fairly late to leaf out and resprout from seemingly dead branches. Then you can remove any branches that might have died as a result of the move without losing any that might still have it in them to bounce back. In the meantime, if the tree is not already mulched, a good layer of mulch of wood chips or dry leaves, about 5cm thick, would probably do it good since it would help moderate soil moisture and temperature, which should help the establishment of a new root system. Also, if your area is fairly dry, irrigation is important to make sure the newly planted tree does not dry out. Crape myrtles, especially large specimens, can be relatively slow to adjust after transplanting but as long as they are alive they are quite resilient, so with good care they should come back well eventually. Once the plant has resumed growth next spring, for example, you can help it along by fertilizing it well. I give my - smaller - crape myrtles a top dressing of compost enriched with some bone or blood meal in late spring or early summer, followed by liquid fertilizer doses every two to three weeks until shortly before they begin to flower.
    I hope all of this helps a little bit. Best of luck with your tree!

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  5. Hi! I planted a beautiful 5 gallon crape mytrle in our backyard about a month ago. Within 24 hours the leaves were wilting and within a week they had all dried up. I've continued watering it and smiling at it :) in hopes that it will come back. Yesterday upon close examination I noticed tiny little buds all over the tree and some green/red branches coming off the tips of the seemingly "dead" branches. Yahoooo! My question is, do you think I should remove the dead leaves or just leave it alone? I live in inland southern California- dry area, summer highs in low 100's and winter lows in mid-30's. Thanks, College Gardener!

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  6. Hi Melissa,

    I would leave the dead leaves and twigs on the plant until the new growth is fairly well developed. The new buds and young branches tend to be quite brittle and easily break off the older wood, so cleaning the tree up now would risk losing many of the sprouting buds. In addition, by waiting a bit you can make sure that all the branches that still have life in them have leafed out, thus avoiding accidentally cutting off any healthy wood.

    I hope this helps - Thanks for stopping by the blog!

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  7. I bought 2 crape myrtles from 2 different stores. 1 is leafing out, the other one isn't doing anything. A friend said if I knick the branches with a knife along with the fertilizer it will promote growth. Is that true? Any tips/help would be appreciated. Thanks

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    1. I have never heard of this knicking-of-the-branches trick, though sometimes stress of this sort might trigger a reaction in a plant. However, I am usually even hesitant to fertilize a plant until it is actively growing. Most of all, though, I would be patient for a while, since even established crape myrtles are relatively late to leaf out in the spring.

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  8. ok thanks -'ll wait until next year and just baby her along. Thanks for the info.

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  9. My crepe myrtles are tall variety, around 30 feet. Will they survive and thrive if I take off the top 20 feet?

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  10. I have two crepe myrtle the have a tall skinny trunk, iv'v3 had rhem for about a year . They came from nursery in con5aine4 iv planted them in my yard . UESTION IS, WHEN WOULD YOU suggest cut the the gardening the holding it to a stake? Also how long before it's sturdy enough to stand upright w/o the stake 9r other support?

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  11. How long does a crepe myrtle need the support stake and gardening tape to keep it upright? Also what is the growth rate of the trunks diameter? This is regarding the tall skinny trunked variety.

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