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Early cold weather to blame for tree holding onto leaves for winter

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Q: Our red maple did not lose its leaves last fall. It is starting to get new leaves now, so I guess that it will be okay. What possibly could have caused this? Will it happen again?

A: You are quite right in thinking that your red maple will be fine. Trees or bushes holding dead brown leaves all winter are a weather-related phenomenon. So, yes, you could see it happen again some year, on the red maple or another plant. It certainly is not common.

What happens is this: Plants like your maple tree, whose branches live all winter, program themselves to drop their leaves each fall. The first sign of their schedule change is the appearance of fall color in the leaves. The trees gradually decrease the amount of chlorophyll they have been producing. They are preparing for winter sleep. As the chlorophyll layer thins, leaf colors which have been hidden underneath the green (or sometimes dark red) of the summer leaves come out of the green shadows. Woods, lawns, and gardens are suddenly blanketed with yellow, orange, and red leaves.

At the same time, an invisible change has been going on. Each tree has been preparing to close down the chlorophyll factory of the leaves for winter vacation. At the bottom of every leaf stem is a circle, invisible to the human eye because it is only one cell thick. This circle of cells gradually cuts off the circulation to the leaf. It finishes its job like the blades of scissors closing, and the leaf falls.

As you know, the fall weather around here is unpredictable. Occasionally we get a very early cold spell instead of gradual cooling. If we have temperatures low enough to kill leaves before the circulation is cut off, the leaves may stay on the tree. They are brown and dead, but the scissor blades never closed.

Since all trees do not program themselves to drop their leaves on the same date, early cold temperatures may catch some trees but not others. Your red maple had not finished its fall work when a very cold morning ended its program.

Leaves left on trees gradually fall during the winter, usually because winds blow them off. If the leaves are too firmly attached for the wind to whip them away, the tree itself will push the dead leaves off in the spring. The tree is making space for new leaves to start growing.

The opposite, the ultimate in leaf-dropping behavior, is sometimes seen in warmer climates than ours. If a tree finishes cutting off the circulation to its leaves and no fall winds have appeared to blow them off, the leaves just drop straight down. Once the tree has detached them, gravity takes over.

Calm and warm fall days can even result in a tree’s dropping all its leaves at once, making a circle of color on the ground at the base of the tree. Ginkgo trees are particularly known for this behavior. One day the whole tree has golden leaves; the next day the bare branches stand above a gold ring on the grass.


Q: What is the flower called Love-in-a-mist? Is it hard to grow?

A: It is an annual, also great for filling in spaces in perennial flower beds. It is incredibly easy to grow, once you have it started.

You may find it difficult to buy plants, since Love-in-a-mist has a taproot; thus it is hard to transplant. Look for seed packets which call it by its botanical name, nigella. Seeds are usually sold as a color mixture. The plants bloom in blue, white, or rose, with blue by far the most common color. They grow to a foot or so in height and almost that wide.

Love-in-a-mist branches naturally. It needs no pinching to shape it. As a matter of fact, it needs nothing except regular watering to put on its show. The flowers nestle into a delicate collar of leaves, like a green ruff under the bloom. The fine, threadlike leaves give the plant its misty look.

If you remove flowers when the petals wilt, the plants will bloom over a longer season. If you leave the flowers, they will develop into delicate, balloon-like seedpods with little horns on top. The pods are much prized for flower arrangements.

In hot climates, Love-in-a-mist is an early flower. In our cool climate seedpods can take all summer to develop. Best news of all for the gardener is that the pods split and scatter their own seeds. Once started, nigella keeps itself going from year to year without human interference. Nigella does not spread like a weed, but it does start enough seedlings to make thinning them a yearly chore. Thin once to give them space. Thin again when the first flowers appear to prevent blue-flowered plants from overwhelming white and rose. Aside from that, simply enjoy their delicacy, both in the garden and as cut flowers.

Asian greens

Q: What can you tell me about growing Asian greens?

A: I love to add them to my summer salads for their variety of flavors. At this time of year my salads are more Asian greens than lettuce. Other gardeners stir fry or steam the greens. I prefer to eat them raw.

Like radishes, Asian greens are quickly grown and best eaten before they become huge. Many of them seem to make flowers overnight, especially in warm weather. They are a spring and fall crop, not a midsummer one. One exception is the mustard green called Indian or southern giant mustard. It produces lush salad greens even in July and August.

There is great variety in Asian greens; experience will tell you which ones you like best. My personal favorites are mizuna, bok choi, komatsuna, and red and green mustards. Except for bok choi, I sow the seeds in dense patches under floating row cover. I remove the cover when the seedlings appear. Harvesting begins with pulling the first plants when they are two or three inches tall. I thin the patch by continuing to pull the biggest plants every two or three days. I try to eat all the produce by the time that it is six or seven inches tall. Bigger leaves are likely to get tough even before flowers appear.

I start bok choi in six packs, setting out plants six inches apart and harvesting the biggest leaves until the plant decides to flower.


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