Ask the Gardener: Amid climate change, this is the best time to plant grass seed

Plus, can these river birches be saved, and here’s why you should not be bagging your leaves.

Christopher Habermann
Grass seed must stay slightly but constantly damp until it sprouts, which takes about 10 days.

What to do this week Trees use the nutrients in your soil to produce leaves, which every autumn drop to earth and decompose back into soil. This is nature’s perfect recycling. But we break this cycle and deplete our soil when we collect and bag our leaves to be hauled away. Why do we do this? Because we have lawns instead of forest floors, and whole leaves can smother lawns. A less wasteful work around is to use a “mulching mower” to break up the leaves where they fall and allow the shards to disappear into the grass as natural fertilizer. This works when you mow frequently. But if the layer of fallen leaves is thicker than one or two deep or is overlapping paving, we rake or blow it into a corner of the yard, then spread it out for mowing into small pieces. Then we rake the bits into a small pile to compost for a year. By the following fall, the leaf bits have decomposed to the stage called “leaf mold.” This is the best mulch there is because it has no weed seeds and is very nutritious, like organic health food for gardens. You can also make leaf piles of whole leaves, but in that case they will take several years to transform and must be penned in or weighted down so they don’t blow away. Wooded areas can be good places to dump such leaves and leave them to decay.


Q. When is the best time to plant grass seed? I have heard it is either in the spring or the fall. If autumn is the answer, when is the best time?

J.M., Hanson

A. Now through the end of October is the best time of the year to landscape, but first check that your municipality will let you water, because once sown, your grass seed must stay slightly but constantly damp until it sprouts, which takes about 10 days. If the seeds dry out before then, they can die, and then you have to start over. Many people seed lawns in the spring, but with the increasing summer droughts and heat linked to global warming, followed by increasingly mild winters, fall planting is looking like the better option. April is my second choice.

Q. I have six river birch trees in the yard, and on half of them, the leaves are turning yellow and dropping. Is it normal in drought periods that this species defoliates early? I water around the trunk and drip lines a couple of times a week. There are still green leaves throughout the tree, especially on the tops. Is this temporary, or are the trees doomed?


D.A., Plymouth

A. Some trees will drop their leaves early during drought. And with rain levels several inches below normal for the year, we are still in a drought. Do not fertilize the trees, because this stresses them by forcing growth and makes them thirstier. But you can continue to help your trees survive by watering them as long as they have leaves on them (and your city allows it). Once all the leaves drop, the trees enter dormancy, and there is nothing more you can do but wait and see whether they come back next spring. Mature trees in leaf need 30 to 40 gallons per month. But new trees planted less than three years ago need that much water per week. Don’t forget to water municipal street trees in front of your house, too, especially if the poor things are living on a “hell strip” (surrounded by pavement).

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