Growing Japanese Maples
Japanese Maples are easy to grow in the hot mid-west if given shade and water. They are very adaptable to a wide range of soils and light. The only serious problems are from long periods of standing water or from long periods of drought or from early or late freezes or from too much sun. The red leaf varieties are especially sensitive to too much hot sun and the small green leaf varieties handle the sun the best. The best site is under high shade with a north or northeast exposure but they will also grow in other locations. They have shallow roots but are not overly competitive and can coexist with many other plants or ground covers in the landscape.
Many Japanese Maples reach a height of 14-20 feet with an equal spread. The dissectums generally reach 6 feet but can spread much more than this. All can be kept at six feet by pruning. If you prune large branches It may take several years to look natural again, so only prune current year's growth for a natural look. Best time to prune is right after fall color through December when you can see all the branches and then make cuts to balance the growth. Light pruning can also be done anytime but mid-May gives you the best chance of getting new growth.
Leaf color is affected by the amount of sun, moisture, nutrients or by the health of the root system. The same variety may even exhibit different colors even when grown nearby when there are differences in any of the above factors. In Japan there are many varieties that color differently in various parts of the country. Red-leafed varieties may get green from too much shade or too much fertilizer or from not enough water. I have found that my best colors occur when there is 1-2 hours of sun with ample moisture, but drying out slightly between watering.
Newly planted maples need a good hand watering once a week, or more if in sun, the first year. Make sure that the root ball you planted is getting wet until the tree has grown roots out into your soil. If your maple fattens-up the trunk a lot in the fall or in the second year, it is a sign that it grew lots of new roots. They prefer to be moist during the hot summer with irrigation about every 4-5 days, but some varieties can stay healthy for up to two weeks without irrigation once they are established. All maples appreciate a consistent watering schedule. When temperatures are cool do not over water, but let them dry-out a little, as this will encourage root growth which helps them when it does get hot. They like the sun when temperatures are below the mid-eighties and they tolerate the hot sun very well until it is consistently above the mid-nineties. High nighttime temperatures are also detrimental to all plants including Japanese maples, especially those in containers, as it deters them from manufacturing food from photosynthesis.
If your red-leaf Japanese maple leafs-out green in spring it is a sign that it is very dry or has a poor root system. Usually watering in winter is not needed, but they do lose a little water even when they are dormant, so water monthly in winter if it is dry. In summer if you see some interior leaves change to fall color it means not all the roots are receiving moisture.
A mature Japanese Maple is rarely bothered by insects or disease. Sound gardening practices, such as good air-circulation, and good soil drainage should prevent any fungus problems. Copper based sprays or all-purpose fungicides may help with limbs that are dying but cannot be used during hot weather. All summer sprays must be applied early in the morning to prevent phytotoxicity. Even the organic sprays are detrimental to Japanese maples during hot weather. Always prune off dead or dying limbs immediately. I do not like groundcovers over my maple roots which may harbor insects and rodents that could damage your Japanese maple.
Japanese Maples like morning sun but do fine as understory trees with high, dappled shade. Metro Maples has the varieties that perform well in those situations. They do not like heavy shade or being crowded by other plants. Some varieties handle the hot afternoon sun well but in very hot years you may get burn in late summer. Most can handle a few hours of midday sun as long as moisture is consistent. Be sure to water extra in late summer or during very hot periods, or before any sudden big change in temperature. Early morning watering is best as there is a time lag in getting the water to the leaves. Some of the red varieties do not hold color as well under heavy shade or too much hot sun. A few varieties need almost full-sun to color well, so grow these in pots then move to shade when it gets hot. I do not sell many of the varieties that must have this treatment. The most sun tolerant varieties have green leaves, such as Seiryu and Sango Kaku but the most sun tolerant is the species itself, Acer palmatum.Red leaf varietes cannot handle dry soils for very long when temperatures are above 95 degrees. If your maple is getting too much hot sun, either water more often or dig it up and move it in November.
Make sure your maple is raised-up a few inches to a foot if you are planting in a low spot or have a water holding clay. Remember, they will not grow in water-logged soil. I like to mix-in lots of aged pine bark and compost to the soil, leaving the area raised-up about 6 inches or more. If your soil is really bad, either keep them heavily mulched, or you can plant them in raised beds of azalea mix (pine bark/peat moss) and then will be able to grow azaleas too.
All Japanese Maples can be container grown. It's best to repot your maple at least every two years, pruning the roots or using a larger pot, and giving them fresh well-draining potting soil. Container grown plants need good drainage and careful attention to watering. Check the drainage hole every now and then and make sure that it is not clogged-up. Every time you water there should be water running out of the bottom of the pot. November or February is a good time to repot. (For my prized maples I sift out the bark dust and the small and large particles, and mix in 50 percent aggregate.) Fertilize lightly with a slow release fertilizer at half the recommended rate or monthly with a liquid at half, or less, the recommended rate depending on the season. Use gypsum for calcium if needed. Occasional use of Epsom salts, at the same rate as your fertilizer, can help release the nutrients to your maple. You might want to protect the roots by wrapping the pot, or move your plant into the garage, if temperatures go below 15 degrees for a long period. Red leaf varieties grown in pots can have leaf burn even in shade when temperatures are continuously very hot for extended periods.
Japanese Maples in the ground do not need large amounts of fertilizer but do like small amounts in spring and fall, and very small amounts in summer. Fertilizer is not food but contain nutrients used to manufacture food through photosynthesis. Maples must expend energy to process fertilizer so never fertilize a damaged tree. Best times to fertilize are about 3 weeks before they start growing in spring, perhaps again in early May, and as soon as you think it has finally cooled-off in the fall. If your tree has been damaged from the summer heat, do not fertilize in the fall, but wait until the following spring. You will not burn them if you only use one-half teaspoon per gallon in summer. A balanced fertilizer, such as 13-13-13, with sulfur, boron, magnesium and the other micro-nutrients works well. Slow release is preferred. Use 1 tablespoon on small plants, 3 tablespoons on 4 to 6 foot plants, and about 7 tablespoons on large ones. Organic fertilizers work very well but may decompose your potting soil too quickly. I have had good luck with cottonseed meal (slow release, high nitrogen), or fish emulsion with seaweed (nitrogen and micro-nutrients but not long-lasting). Root stimulators with some nitrogen and lots of phosphorus work very well on dissectums. This can also be used in September (when it cools-off) to help harden and fatten the branches. Despite what some people say, synthetic fertilizer does not kill the beneficial soil fungus. Rain also has nitrogen, especially in the city from the nitrous-oxide from automobile emissions.
Water your maples early in morning as there is a lag time in supplying the leaves with the moisture.
Micro-climates are areas that are different from the normal situation. Shade, fences or houses to block winds, and lots of vegetation to humidify and cool the area, all create a favorable micro-climate for your maple. Trees do not like sudden large swings in temperatures and it takes them a week or two to adapt.
Beware of squirrels in late summer chewing-off the bark which can kill the tree. I use cayenne pepper sprays mixed with a spreader sticker, so that it will last longer.
Japanese maples like a consistent amount of moisture. They do not like long periods of ample moisture followed by long periods of drought. Excessive spring rains or watering or excessive fertilizing can reduce root growth which then lessens their ability to handle dry periods in summer, so whatever you do, do not stop watering in summer when they are used to being wet. In the shade they can be grown on small amounts to large amounts of water but the water supply needs to stay consistent.