Gadenin日本語Get the appMatch the site to the mature size, not the pot
This plant comes in a very wide range of mature sizes, from dwarf forms that stay around three feet (1 m) to tree forms that reach twenty-five feet (7.5 m) with a spread almost as wide. The plant in the pot gives you no hint of which you have, and a tree-form plant put four feet from a house wall or under a window is the origin of nearly every topped crape myrtle you see.
Find out the mature height and spread before you dig, and give it that full width. If the plant will be twenty feet across, its center needs to be at least ten feet from the wall, the path and the neighboring shrub. This one decision removes the pressure to cut it back every year for the rest of its life.
Think about what is above the site as well. A plant grown up under wires or eaves will be topped by someone eventually, whatever your intentions.
| Form | Mature height | Distance from a wall | Spacing between plants |
|---|---|---|---|
| Dwarf shrub | 3 to 5 feet (1 to 1.5 m) | 3 feet (1 m) | 3 to 4 feet (1 to 1.2 m) |
| Semi-dwarf | 5 to 10 feet (1.5 to 3 m) | 5 feet (1.5 m) | 6 to 8 feet (1.8 to 2.4 m) |
| Small tree | 10 to 18 feet (3 to 5.5 m) | 8 to 10 feet (2.4 to 3 m) | 10 to 12 feet (3 to 3.7 m) |
| Full tree form | 18 to 25 feet (5.5 to 7.5 m) | 12 feet (3.7 m) or more | 15 to 20 feet (4.5 to 6 m) |
Full sun and moving air
Six hours of direct sun is the minimum and eight or more is what produces a full display. In less than that the plant grows perfectly well, stretches, and flowers thinly or not at all, which is a slow and confusing failure because nothing ever looks ill.
Air movement is the second requirement, and it is not a detail. A plant tucked into a still corner or squeezed between larger shrubs gets powdery mildew on its flower buds most summers, and mildewed buds do not open. Open air on three sides is worth as much to this plant as a fungicide.
Choose a spot where the trunk display will be seen. The peeling bark is at its best in midsummer and again through winter, and it is wasted at the back of a border. Near a path, a seating area or a window is where the plant earns its keep.
Soil and drainage
Crape myrtle is undemanding about soil type and tolerates a wide pH range, but it will not accept wet feet. Standing water for even a few days in winter kills the roots, and there is no treatment once the plant starts wilting from rot.
Test the site by digging a hole a foot (30 cm) deep and filling it with water. If it has not drained within a few hours, plant on a raised mound eight to twelve inches (20 to 30 cm) high rather than in a hole, or choose a different spot.
Do not fill the planting hole with bagged compost or potting mix. A pocket of soft rich material inside heavy native soil holds water and discourages roots from leaving it. Backfill with the soil you dug out, and put the organic matter on top as mulch instead.
Setting the plant
Plant in autumn where winters are mild, so roots establish through the cool season, or in early spring elsewhere. Avoid planting in the heat of midsummer, when a new root system cannot keep up with the leaf area.
Planting depth is the detail people get wrong most often. The flare where the trunk widens into the roots must sit at or slightly above the finished soil level. Buried too deep, the plant sulks for years and is prone to rot at the base.
- Dig wide, not deep Make the hole two to three times the width of the root ball but no deeper than the root ball is tall. Roots spread sideways; digging deep only guarantees the plant settles and ends up too low.
- Open up a pot-bound root ball If roots are circling the outside of the ball, slice down through them in three or four places with a knife and pull the outer roots loose. Circling roots left intact keep circling and slowly strangle the trunk.
- Set the flare at or above grade Lay a straight edge across the hole to check. On heavy soil, set the top of the root ball a couple of inches (5 cm) proud of the surrounding ground and slope soil up to it.
- Backfill and water in Firm the native soil in gently and water thoroughly to settle it and remove air pockets. Do not tread it down hard; compacted backfill is as bad for roots as an air gap.
- Mulch, keeping the trunk clear Spread two to three inches (5 to 7 cm) of bark or wood chip over the root area, out to the edge of the canopy. Leave a hand's width of bare soil around each trunk. Mulch heaped against bark keeps it wet and invites rot.
- Water deeply through the first two seasons A slow soaking once or twice a week during dry weather for the first two years. After that the plant is markedly drought-tolerant and needs watering only in prolonged drought.
Do not fertilize at planting. A new plant needs to grow roots, and nitrogen at this stage pushes top growth the root system cannot support. Wait until the following spring, and then feed lightly if at all.
What to write down on planting day
Record the position, the date, and above all the mature height and spread stated on the label. That last figure is the one you will want in three winters when someone suggests cutting the plant back because it is getting large. Knowing the plant is doing exactly what it was expected to do is what stops a bad decision.
Also note which direction gets the least air movement and how many hours of direct sun the spot receives in midsummer. Both of these predict where mildew will start, and they let you plan the thinning cuts before there is a problem to react to.