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Archive for November, 2013

Fall leaves cover the lawn

This past weekend I spent several hours blowing the oak leaves out of our front perennial beds and off the front lawn and into the woods beside the house. The leaf cover in the back yard was much lighter so I used our mulching mower to chop them up and then used the lawn sweeper to collect the chopped leaves. These shredded bits of oak and hickory leaves were added to our compost pile. Good stuff for the garden next summer.

Deciduous magnolia broken in an early fall snowstorm.

Deciduous magnolia broken in an
early fall snowstorm.

This whole process got me thinking about the science behind leaf drop in autumn. It’s a rather fascinating story. Can you imagine what it would be like if the leaves on our deciduous trees didn’t drop off in the fall? Many have first hand knowledge of the destruction that can take place when snow and ice storms occur in the early fall before the leaves have fallen from the trees. Definitely not healthy for the trees!

Leaves are the food factories of plants. The green color that you see in most leaves comes from a plant pigment called chlorophyll which is responsible for absorbing sunlight to initiate the process of photosynthesis; a chemical reaction that converts carbon dioxide and water into simple sugars. These simple sugars are then converted into more complex carbohydrates. Photosynthesis is quite possibly the single most important chemical reaction in nature as it provides the ultimate source of food for most organisms.

The tender young foliage of this tree peony is red from anthocyanin

The tender young foliage of this tree
peony is red from anthocyanin

Most people know about chlorophyll but there are two other groups of pigments found in the leaf; the carotenoids, which include carotene (orange pigment) and xanthophyll (yellows and tans), and the anthocyanins which are primarily reds and purples. While the carotenoids are found in the leaf throughout the growing season, the anthocyanins are mainly present in the leaf during the spring and fall. Anthocyanin is responsible for the brilliant reds and purples in the fall and the reddish tint commonly seen in newly emerging leaves in the spring. It is thought to function similar to a “sunscreen” for these tender young leaves – an interesting tidbit of knowledge!

As the chlorophyll breaks down in this hickory, the yellow xanthophyll shows through.

As chlorophyll breaks down, the yellow
xanthophyll begins to show through.

Throughout the spring and summer, high levels of chlorophyll in the leaves normally mask the colors of the other leaf pigments causing the leaves to appear green. In the fall, as the days get shorter and the intensity of the sunlight decreases, changes begin to occur in the leaves. Photosynthesis slows down and chlorophyll production ceases. As the chlorophyll breaks down, the other pigments begin to show through. This is when we start to see the colorful changes in the leaves.

Oak branch in fall. Note the buds that will sprout new growth in spring.

Oak branch in fall. Note the buds that will sprout new growth in spring.

In actuality, it’s the longer nights of fall not the cooler temperatures which are the main trigger for these physiological changes in the leaf. As the nights become longer, a layer of cells (the abscission layer) begins to develop where the leaf petiole (leaf stem) joins the branch. The growth of these cells begins to restrict the movement of sugars out of the leaf and the flow of water and minerals into the leaf. This is the beginning of the end for the life of the leaf! It is slowly being cut off from the main part of the tree – its usefulness is basically over.

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By autumn, the leaves have fulfilled their task of producing food and supplying it to the buds, branches, stems, and roots. The buds for next year’s leaves have been produced and will survive the winter because they are protected by tough bud scales.

Fallen oak leaves cover the ground.

Fallen oak leaves cover the ground.

The leaves of deciduous trees become a liability in winter. Trees lose a lot of water through their leaves – water that would be hard to replace in the winter when the water in the ground is frozen. If the leaves were retained, the tree would slowly die from dehydration. Besides, these thin, tender leaves can’t withstand freezing temperatures anyway, so – they are shed from the tree. Eventually the abscission layer completely blocks off the leaf, weakening the junction between leaf and branch, and the leaf falls; either under its own weight or when wind or rain knocks it off.

Snow falls through leafless trees

Snow falls through leafless trees

An added benefit of the autumn leaf drop is that, without their canopy of leaves, these trees do not hold heavy amounts of snow after a storm. Snow tends to fall right through the bare branches with very little accumulation. If the leaves were still on the trees … well, you know how that ends up!

But what about evergreens, you ask. Why don’t they lose their leaves? How do they survive the freezing temps?

Interesting questions with equally interesting answers!

Flexible evergreen boughs bend under the weight of snow preventing heavy accumulation

Evergreen boughs bend under the
weight of snow to reduce accumulation

Evergreen leaves/needles survive the winter because they are protected by a thick, waxy cuticle. This heavy coating also helps to reduce water loss from the leaves. In addition, rather than the thin, watery sap that is found in the cells of deciduous leaves, evergreen leaves have a kind of “antifreeze” in their cells that protect them from freezing. Cool, huh!

And as far as retaining heavy amounts of snow, evergreens (at least the needled evergreens) tend to have a conical shape with flexible boughs that quite easily shed heavy accumulations of snow. When the snow melts, the branches spring back up.

Ain’t nature wonderful?

Happy Thanksgiving everyone!

Until next time – Happy Gardening!

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Winter squash

Well, not too many vegetables compare to vine ripened tomatoes in the summer but summer is over and the winter veggies rule now! Winter squash, cabbage, kohlrabi, kale, yummy root crops like carrots, beets, and parsnips …

Potato harvest

Potato harvest

I just dug the last of the potatoes in our vegetable garden this past weekend. I got a pretty good haul but one of the rows suffered from the excessive rains we had in June. It was the lowest row which stayed pretty soggy for a while. Most of the potatoes in that row seem to have rotted over the summer.

The white Kennebec potatoes did especially well – the Yukon Gold’s not so well. At least we got lots of Kennebec’s which are my favorites!

While I was digging the potatoes, Eric picked the rattlesnake beans that he had left on the vines to dry.

Rattlesnake beans are a delicious heirloom pole bean - my favorite.

Rattlesnake beans are a delicious
heirloom pole bean.

We will use some of the dried beans in soup and save some to plant next spring. That’s the nice thing about the heirloom varieties; you can save the seed from year to year which saves having to buy new seed every spring. Check out my blog post about heirloom vegetables vs. hybrids. There are loads of delicious heirloom veggies and we have started growing more of them in our garden – especially tomatoes. ‘Kellogg’s Breakfast’ is my new favorite for Swiss cheese and tomato sandwiches – my stock lunch during tomato season! Yum!

Winter squash harvest

Our winter squash harvest

While he was rummaging around the garden picking beans, Eric discovered a few butternut squash that he had missed when he harvested the winter squash back in early October. We got a whole cart full of winter squash back then. Most were butternuts but we also harvested some acorn squash, ‘Delicata’, and small hubbard squash. Normally we would have left them in the garden a few weeks longer, but the woodchuck was showing signs of activity in the vicinity of the garden and we didn’t want to share our squash with that crazy varmint!

While I had the digging fork in hand, I also decided to harvest my carrots and beets. The beets were pulled up without digging but the carrots pull up much easier if you loosen the soil around them slightly with the fork. I could have left them in the ground for a while longer but decided I didn’t want to risk having them chewed on by some critter.

Lynne's carrots covered with shredded leaves

Lynne’s carrots covered with
shredded leaves

Many of the root crops like carrots, turnips, rutabagas, and parsnips can remain in the ground through the fall and into winter as long as they are protected from freezing temperatures. The benefit of leaving them is that when these vegetables are kept growing during the cool nights of fall, they begin to accumulate more sugar in the roots. This results in crisp, sweet carrots, yummy “snips” (as Grampa would call parsnips), and delicious rutabagas and turnips.

The important thing is to cover them with straw, leaves, blankets, or anything that keeps the roots and soil from freezing while leaving just the green tops exposed. Since beets often push up above the ground as they grow, it is important to cover them with soil before covering with the mulch. If the “shoulders” of your carrots or other root crops are exposed, be sure to cover them with soil, too, before mulching them.

Even after temps dipped down to 16, the soil was still nice and workable.

Even after temps dipped down to 16, the
soil was still nice and workable.

My sister Lynne is doing this with her carrots in her vegetable garden in Vermont. Just before the first hard freeze, she piled about 6″-8″ of chopped leaves on top of her carrots leaving just top of the greens exposed to the sunlight. Chopped or shredded leaves are less likely to blow off with fall and winter winds. Another trick is to simply  surround your root crops with bagged leaves to keep them from blowing away. Be sure to leave the green tops exposed so they can continue to photosynthesize and produce sugar which will be stored in the roots making them nice and sweet.

So far it has gotten down into the mid-teens up there and her carrots are still nice and cozy under their leafy blanket. The ground has remained loose and unfrozen and her carrots are becoming sweeter by the day! As it gets colder, she will increase her leaf covering to about 12″ to keep the ground from freezing. Here’s what she wrote me yesterday:

The difference in taste from the ones I just dug and the ones still in the fridge from before we had these really cold days is marked – these are so much sweeter. And they are so crisp and nice!

She is planning to leave some of them in the ground for a Thanksgiving and maybe even a Christmas treat. I can’t wait to enjoy some at Thanksgiving in a few weeks! Better save me some Lynne!

Until next time – Happy Gardening

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