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Ask the Gardener: Why some trees didn’t drop their leaves

Ask the Expert Gardening
Japanese-Maple-Leaves-Fall
Leaves of a Japanese maple tree in full color in a Pembroke front yard. John Tlumacki/Globe staff/File

What to do this week: Start seeds for annual flowers and vegetables indoors. Clean up yard debris. Pull back mulch and snip off last year’s dead leaves from the crowns of emerging new perennial growth. Remove burlap wrappings from evergreens. Cull, clean, and sharpen garden tools and oil the sharpened blades to prevent rust. Put up bird boxes for nesting. One and a quarter to 1½ inches is the best diameter for entry holes, and there should be no perch. (They just provide a landing platform for larger predators to attack nestlings.) Spread gardens with a layer of compost on top.

Q. We have a 15-year-old dwarf Japanese maple, and most years it is a beautiful red in the fall, but in the past two years, the leaves have turned a light brown and stayed on the tree. I have noticed others in the neighborhood have the same problem. What is causing this?

P.H., Belmont

A. One possibility is that the warmer autumns we have been experiencing may be preventing some kinds of trees such as oaks, beech, and your Japanese maple from dropping their leaves. These are all trees that take a long time to prepare for winter. They drop their leaves relatively late in the fall. The wacky warm weather may be throwing off their timing, so they do not finish forming the abscission layers between the twig and the leaf stem that is necessary to release the leaves from the tree. There is a name for this: “marcescence.’’ The good news is that it doesn’t injure the tree. If winter winds haven’t removed them, new buds will push them off in the spring, when the old makes room for the new.

 

Q. A local farm is offering free composted manure to gardeners. I have covered my raised beds with 3 to 4 inches of the compost, which is made from cow, goat, and sheep manure, plus the sawdust and straw that the farmer used to keep the bedding dry. Do I need to add anything, such as more lime, to “temper’’ the compost? Should I till it in or just leave it as is? It appears to have broken down quite a bit, but you can still make out some of the straw and see the color of the sawdust.

W.K., Yarmouthport

A. I also have gotten such a mix from a local farmer, and it is typically about 20 percent manure and 80 percent bedding. The problem is the sawdust. This takes several years to break down, during which time it is sucking nitrogen from the soil and starving your plants. So you should treat the entire mixture as a mulch to suppress weeds and lock in moisture. Spread it on top of the soil between (but not touching) plants. NEVER till it into the soil. These days people are turning away from digging and tilling and instead just layering soil amendments on top of their gardens. This doesn’t rip up beneficial soil fungus that helps plants grow. Also, tilling soil can release stored carbon into the atmosphere, contributing to greenhouse gases. The new attitude is that soil should always be covered, either by growing plants or by mulch, and never left exposed to the air. I would sprinkle lime on top of the farmer’s gift, and also some 10-10-10 fertilizer according to package directions to counteract the acidity of the sawdust and manure and add supplemental nitrogen. If you can get bedding that includes just straw but not sawdust, that would be better. Hay often contains seeds, but straw usually does not, so it is better for gardens though usually more expensive. I would not buy sawdust, but “free’’ is tempting. Handle it with care.

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