WICHE: Roller coaster of wet, cool, dry and hot

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By Jeneen Wiche

According to our weather forecasters, it looks like we are getting ready for another swing in our weather.

The cool, wet weather pattern was great for my peas, greens and potatoes; but I am starting to think maybe I should have waited one more week before putting the tomatoes and peppers out.

Our roller-coaster ride from hot and dry to cool and wet and back again is good news for some and bad for others.

So how do precipitation and temperature affect plants? Well, in every way possible.

Excessive precipitation, especially in poorly drained soils, can restrict oxygen intake by roots. Oxygen is critical for all other processes to occur that impact growth and vigor.

In years where we have experienced excessively wet springs we typically see stunting and yellowing in herbaceous plants. The rain is great for woody plants and new spring growth, but it can put them at a disadvantage later in the season.

Wet springs encourage feeder roots to development closer to the surface of the soil (where they can get more oxygen), which means that they may be more susceptible to drought stress if the summer turns dry.

All the important plant processes react to temperature, as well: photosynthesis, transpiration, respiration, germination, and flowering. How temperature affects these processes depends on the plant, of course, some like it hot; some like it cool.

Most of us can make a distinction between cool season crops like spinach, Brussels sprouts and peas. And warm-season crops like green beans, cucumbers, corn, peppers, eggplant and tomatoes.

The origin of these plants has much to do with their physiology. For example lettuce becomes bitter and begins to bolt as temperatures increase. The same cool temperatures lettuce likes will actually cause tomatoes to experience a chemical reaction that slows photosynthesis during the day and delays the breakdown of starch into sugar at night.

Cool nighttime temperatures for plants that like it hot can cause them to stop growing and arrest root development and flowering.

On the other hand, cool night temperatures may be just what your potatoes need to have the best yield ever.

Researchers in Alberta, Canada have discovered that potato plants respond positively to cool night temperatures, increasing yield and quality. Should be a good new potato harvest early this summer, at least!

In some instances, low temperatures require less energy use by a plant while an increase in sugar storage occurs. This means that root crops like beets, parsnips and carrots may be sweeter then ever at first harvest this summer; they become less sweet as the heat rises.

And, interestingly, parsnips are best left in the ground until we have had at least three hard freezes to sweeten them up before harvest.

So it seems that, if you are from a warm place originally, you will not respond well to unusually low nighttime temperatures. But if you are from a more temperate climate it is just what you need to be a perfect plant.

When our weather flip flips so frequently it is hard to please everyone, but it is an argument for being patient about getting your summer crops out.

You can also focus on the cultural health of you garden by improving your soil tilth and drainage (using composted manures) and use a chunky mulch that allows good oxygen penetration.

This will offset yellowing and stunting of herbaceous perennials that may other wise get waterlogged.

If you have some summer crops in a stunted state, consider warming them up on cool nights with a min-greenhouse, bucket or a circle of water-filled milk jugs as insulation.

That works well enough until the heat is upon us.

And I concede that each season is a balance of sorts…when it comes to plants some will thrive some will not. I’ll take what I can get either way.