WICHE: Don’t rush the summer vegetable garden

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Want to start planting those tomatoes? Better slow down a bit.

I am heading to Boulder, Colo., for a Slow Money National Gathering Conference, and at writing they are melting a record April snow fall. A warming trend occurs before my arrival, thank goodness. Our cold spring met with a blizzard in my destination that is the one opportunity I have to get away for some continuing education this year does not sit well.

While there is much to be done in the spring garden and our surrounding landscape, the cool season has helped to slow the sometimes frenetic pace. I am so not ready to get any summer vegetables in because it is simply too cold. Plus, we must consider the soil temperature, summer crops will not germinate by seed nor will their roots thrive in cold soils.

Hold off on the tomatoesa bit longer if you do not want them to languish.

Two things that can set you back in the vegetable garden from the start: poorly prepared soil and seedlings set out too early. Soil temperature has a great deal to do with how well your crops germinate, establish and produce.

Because we don’t live in the soil (for some of us I suppose this could be debated), we are not as tuned in to the importance of soil temperature. Sure, we know ambient air temperature and once it is above 65 degrees, something in our brains is triggered, and we want to start our vegetable garden straight away – be patient for some crops.

Cool season crops are out: potatoes, onions, leeks, and some greens. But it is still too early for tomatoes, cucumbers, beans, squash and other summer crops.

The fact of the matter is that certain seeds simply will not germinate until soil temperatures reach 70, 80 or 90 degrees.

Because tomatoes are likely the most popular summer vegetable (and the one that typically gets planted too early in some gardens) this example may be useful. Tomatoes are picky about soil and ambient air temperature. Research conducted by the USDA-Agricultural Research Station in Urbana, Ill., revealed some interesting facts: Anything below 55 degrees screws up the circadian clock of the plant.

Once the circadian clock is discombobulated the tomato’s ability to photosynthesize during the day and process the starch into sugar at night is delayed within the regular 24-hour cycle. The photosynthetic metabolism of a plant that has been subjected to nighttime temperatures below 50 degrees starts to photosynthesize later in the day, and the processing of the starch starts later in the night, and the whole cycle gets displaced to the point that the plant languishes.

One sign of cold stress for a tomato plant is purple-tinged leaves. I have had plants with purple tinged-leaves. They look robust and healthy, but they never produced much. It seems, too, that temperatures below 55 degrees also renders the pollen of a tomato flower useless (high heat will do this, too). No fertilization of the flower, no tomato.

The reality is that gardeners are excited to get gardening in the spring, so how do we effectively get everything we want: an early start, healthy plants and a good harvest. There are ways to plant early and ensure that you keep your plants warm.

Heat the soil, first, by putting down black plastic. Use a cleverly constructed cold frame system out of some household items. You can create your own “wall-of-water” heating device by filling gallon jugs with water and lashing them together in a circle around your plants (or you can buy the pre-made plastic “wall-of-water” device).

The water will heat during the day and release the warmth overnight, keeping your tomato plant warm.


Check out gardening columnist Jeneen Wiche’s work at www.SwallowRailFarm.com. You can find her columns also at www.SentinelNews.com/agriculture. She answers questions once a month in SentinelNewsPlus. To submit a question, send an E-mail to jwiche@shelbybb.netand type “Sentinel-News” in the subject field.