Garden Plot: Tree planting and leaves on the lawn

Is it still tree planting time?

Jane in Woodbridge, Virginia, keeps it simple. She writes:

“Is it too late to plant new trees?”

No, Jane — the only bad time to plant new trees is in the summer, when they struggle with transplant shock in the heat. The BEST time would have been back in September, with early Spring a close second, but wintertime is fine as long as you can dig the hole.

That said, I would wait until the middle of next week, when we’re expecting a warming trend (Highs in the fifties! Break out the sandals and shorts!).

If the long-range forecast is correct, the absolute perfect day would be Thursday. The soil should be nice and warm by then and the weather-guessers are calling for rain on Friday, which is ideal. Even at this time of year, it’s important to keep newly installed plants well-watered.

How to plant a tree

When planting time arrives, dig a wide hole, not a deep one. If the tree is ‘balled and burlaped’, remove and discard all the wrappings. If it’s in a pot, pull it out and remove soil from the top until you can see the root flare — the spot where the trunk meets the top of the root system.

Place the tree in the planting hole; if it looks like a lollipop, add dirt to the bottom of the hole and try again; you want the top of the root flare to be visible above ground.

Do NOT pile mulch up against the trunk of the tree. Mulch should be spread an inch or two deep beginning six inches away from the trunk. Really.

Why you should plant a tree the way I just said

The dormant period is a fine time to install new trees and shrubs, but do it correctly. To explain the advice above:

  • The planting hole should NOT be amended with compost, perlite, potting soil or any other nice stuff. You want your tree’s growing roots to have to deal with the soil you have, and that crappy soil is all that should go back into the planting hole.
  • Plant high, not low. I know its counterintuitive, but trees that look like lollipops are much more prone to falling over than trees where you can see the root flare — the area where the top of the root system meets the trunk — above.
  • And finally, do NOT volcano mulch your trees! This decorative disaster leads to a short and unhappy life for the poor tree. No mulch should ever touch a tree. The reason you mostly see the opposite? Horticultural ignorance of the most foolish degree.
  • PS: If you ever see a tree in nature with a blankie rotting the bottom of it’s trunk, let me know.

Will mowed leaves harm a lawn?

Doug in Adamstown, Maryland, writes:

“What’s your feeling about the leaves on my lawn? Rake and compost? Or mow into the lawn? I get about an ankle-deep layer of leaves, which I previously just mowed into the lawn with my mulching walk-behind mower. After a few hours, the shredded leaves settle into the lawn, out of sight. The trees are: Elm, Pin Oak, Maple, and a flowering Cherry. But I’ve noticed, after many years of doing this, that the grass does not grow well around the oak. Could the acidity of the leaves (Doug’s assumption) be affecting my soil, and should I apply lime in those areas?”

Not without a soil test, Doug. As trees mature, grass typically does not grow well directly beneath them. And if a soil test does show that the area is acidic, yes — apply lime or even better, ash from a hardwood stove.

More about leaves and lawns

Mulching fallen leaves back into the lawn provides a wide range of nutrients and helps break down any thatch that’s present. Get a soil test, and if the result is below 6.5* you can apply lime — although ashes from a hardwood stove do just as good a job while providing added nutrients.

And be aware that as trees mature, grass will always struggle to grow beneath them.

The pH scale is a measure of acidity vs alkalinity. The number seven is both lucky on the first roll of the dice in a crap game and for the majority of plants as seven is neutral — neither acidic nor alkaline. A pH level of 6.5 is just as good, as most plants do well in a soil that’s mildly acidic. But numbers lower than six will cause many plants to struggle — the exceptions being the ‘acid-lovers’ like blueberries, azaleas, rhododendrons and a few others; they require a pH of six or lower to thrive.

For other plants — like lawns — you want to get back up to 6.5 or seven, and to do so you add lime or wood ash to raise the pH. Numbers above seven (alkaline) are rare in our area and are almost the result of overuse of lime.

Do NOT lime without a soil test!

Mike McGrath was editor-in-chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated public radio show “You Bet Your Garden” since 1998 and WTOP Garden Editor since 1999. Send him your garden or pest control questions at

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