Monday August 19, 2013 | 09:15 AM
Posted by David Epstein

It wasn’t a beach day across southern Maine yesterday as a frontal system just offshore allowed clouds to hold tough for much of the afternoon.  I kind of like days like that as they tend to slow me down and also allow me to work outside without the heat we can experience in mid-August.

I'll be updating the details of the weather and the best places for leaf peeping on Twitter at @growingwisdom Please follow me there. Feel free to comment or ask questions too.

The weather this week looks quite fabulous with abundant sunshine and warm temperatures.   I expect many of us to reach the 80s today through Thursday.  You will notice more moisture in the air this week, especially Wednesday and Thursday.   

We will transition to cooler less humid weather for the weekend when highs will only reach the 70s with abundant sunshine.  I don’t see any significant rain in the forecast for perhaps as long as 10 days.

All this dry weather is going to start to cause minor issues with lawns and some other plants which might need more regular rains.  However, it has been such a wet summer a major drought is unlikely. As long as we don't get too dry, this may also help with our next big tourist event, leaf peeping!

Fall Foliage Preview

The cool nights and warm days of the past couple of weeks may have been a contributing factor in bringing some early color to a few trees.  Generally, trees and shrubs that show color in early to mid-August are under some sort of stress from disease, heat or insects that brings on the change in color.

Remember, the purpose of the leaves on plants is to make food (simple sugars) for the plant to survive the winter and leaf out again next spring.   The transfer of food from the leaves to the branches and roots of a tree takes place from the time they leaf out in spring until sometime in late summer and early fall. 

Additionally the roots are taking up nutrients from the ground and sending it to the leaves to make chlorophyll.  Chlorophyll needs to be constantly replaced during the spring and summer. The chlorophyll is what take in the sunshine and continually make more food to get your favorite shade tree through the upcoming winter.

Over the next few weeks a layer of cells, called the abscission layer, will rapidly grow and basically damn the flow of sugars from the leaves to the rest of the tree.  The layer not only block to the flow from the leaves downward, it will also block the flow of nutrients from the tree into the leaves.  As this happens, that green pigment, the chlorophyll, can no longer be manufactured.  Without the Chlorophyll the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season.

This is different than the red and purple pigments which come from anthocyanins. In the fall anthocyanins are actually manufactured from the sugars trapped in the leaf.  In most plants anthocyanins are typically not present during the growing season.  

The best weather for great color for September and October will be generally dry, but not too dry.  A wet second half of August and September will not be good for fall color.  We also need to have cool nights, but not frosty nights for optimum color this fall.  So far, we are on track for a great season ahead, but of course it could all come crashing down with one big early season storm.

Gardening this week Tomato and corn season is upon us here in New England and the produce is wonderful. My own tomatoes are now coming to maturity and the video below is an update to one tomato plant I rescued last fall from a sidewalk at Framingham State. The plant was growing in the crack of the concrete and I kept it alive all winter. I'll be updating the details of the weather on Twitter at @growingwisdom Please follow me there. Feel free to comment or ask questions too.

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About the Author

David Epstein has been a meteorologist for more than 25 years. He spent 16 years in Boston and currently freelances at WGME13 in Portland.

In 2006, David founded, a business producing educational and marketing videos for the green industry. He currently is a professor at Framingham State College, teaches Jan Plan at Colby College and owns Bloomscapes Inc., a landscape design business.

David authored "Gardens Of New England" and his work has been published in Grolier's Science Annual for 10 years. He lives in South Natick, Mass., and has a summer home in Harpswell.

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