Hot Summer Grapes

The hot summer is good, to an extent.

While you and I here in South Jersey have been sweating it out for the last few

weeks, the grapes have been thriving. Grapes flourish in the warm weather and can put a

lot of energy into ripening berries and producing new vegetative growth (something that

is not ideal if you want to make wine but there are ways to manage very leafy plants).

Plants will continue to thrive in this weather and harvest will be a little early if this

warmth sticks around for a few more weeks. And one of the biggest bonuses of the

warmth is bacterial disease like Downey Mildew and Black Rot are hindered by above

+90 O F temperatures. Any hotter though and the vines will start to feel the extreme heat


Around 100 O F to 105 O F plants begin to slow down as photosynthesis begins to

cost the plant water. If a plant continues to loose too much water it begins to wilt. To

prevent this, the plant will close its stomata (similar to pores in the skin). With the

stomata closed the plant can not take up CO 2 and photosynthesis grinds to a halt. When

the temperature drops low enough the stomata open and photosynthesis resumes.

Now for those of you thinking, “What happens to plants in hotter climates where

triple digits are common?” There are 3 types of photosynthesis, known as C3, C4, or

CAM. C3, which is the type grapes (V. vinifera) have, is the simplest from an

evolutionary standpoint and suited for cooler climates. C4 and CAM differ but both are

better suited for warmer climates. Sugarcane and cactus are examples of C4 and CAM


-Brian Tomasello 4th Generation Outer Coastal Plain Winemaker Tomasello Winery


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