If you own a Japanese maple tree, or pass by one on your daily strolls, check the leaves. Are they getting a little brown around the edges? Are the leaves beginning to fall off? Welcome to late August and early September, where the quadruple whammy of triple digit temperatures, hot dry winds, reflected heat from a nearby wall/concrete surface, or irregular watering can make many Japanese maples start to suffer. Note the location of those Japanese maple trees. Are they in full sun more than six or eight hours a day? Is it facing a direction where winds are common in the hot afternoon? Around here, it is primarily west and southwest winds.
Although most Japanese maples prefer morning sun and afternoon shade, there are several varieties that can take the full sun.
Chris Aycock of El Dorado Nursery and Gardens in Shingle Springs, CA has his favorite Japanese maples for sun or partial sun. “An old standard is the ‘Bloodgood’ Japanese maple,” says Aycock. “It gets about 20 feet tall and wide. If you want something smaller, ‘Fireglow’ is a nice 12 to 15 foot, upright growing variety. If you're looking for a lace-leaf Japanese maple, ‘Orangeola’ is one of my favorites. It's a very fast growing, cascading lace-leaf-style Japanese maple, with orange-red foliage. It’s very tough and very vigorous.” Hear more of Aycock’s comments and tips about Japanese maple trees in today’s newsletter podcast (above).
Scott Paris of High Hand Nursery in Loomis, CA says he has found three Japanese maples for sunny areas in Northern California: ‘Seiryu’, ‘Pine Bark’, and ‘Tobiosho’.
“The ‘Seiryu’ is amazing,” says Paris. “It is the only upright growing lace-leaf variety. With its beautiful red fall color, it is a showstopper. When stressed in the heat, it is very rare that it flags. Instead, it gets a cinnamon hue.”
Paris is also high on the ‘Pine Bark’ Japanese maple. “This has cool-looking leaves, and the bark resembles a pine tree, with stunning red fall color.”
One of Paris’ most consistent performers among Japanese maple trees is the ‘Tobiosho’. “It’s a basic green maple in the summer,” Paris explains. “People usually cruise by it and yawn. But no, this maple is a consistent grower with outstanding fall color.”
That’s good information if planting a Japanese maple is on your fall to-do list. But for those with suffering Japanese maples right now, here are some do’s and don’ts.
• If the leaves on the Japanese maple tree are browning, fight the urge to pull them off. Those browning leaves, while hanging on the tree, can help the tree avoid sunburn to the branches and trunks.
• Be careful with watering. Check the soil moisture at a depth of eight or 10 inches before you irrigate. Japanese maples need regular watering, but too much standing water can lead to soil-borne diseases in the root area.
• Remove any lawn beneath the tree that is competing for the water. Because turf roots are shallower, they will get first dibs on any water from sprinklers or drip irrigation systems.
• Add mulch beneath the tree to help preserve a more consistent soil moisture level. Arborist Anne Fenkner of Davey Tree Company suggests the “4-4-4” rule for mulching beneath trees: “Place wood chips that are four inches deep, starting four inches away from the trunk of the tree, and extend that mulch four feet out all around the tree.”
• Aycock seconds that mulching motion, with an added tip: “Mulching is very critical, it helps keep the roots cool. Although we will recommend full sun for quite a few of the varieties, we will tell you to plant it away from the house so there's no reflective heat. You're better to have it out in the open rather than up against a hot wall.”
• Don’t fertilize a suffering Japanese maple in the heat of the summer. The best season for a single application of fertilizer for Japanese maples, according to Paris, is spring. “Japanese maple trees are not greedy,” says Paris. “But maples resent quick-release ammonium sources of fertilizer. Apply in early spring and not more than once a year.” All-purpose, slow-release organic fertilizers, usually with nitrogen, phosphorus, and potassium content in the single digits, are widely available. Remember, too, that as the mulch layer around your Japanese maple tree breaks down, it is feeding the soil, too.
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Fred Hoffman is also a University of California Cooperative Extension Master Gardener in Sacramento County. And he likes to ride his bike(s).
Japanese Maples vs. the Heat of Summer