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garden:infrastructure:lowtents:temps

Temperatures

Extended growing

I use the low tents to extend the growing season for suitable plants-those that have some cold tolerance but which might be killed or stunted by a hard frost. In 2015 I grew mostly lettuce, chard and bunch onions in the tents. Lettuce transplanted on April 3 did remarkably well. We harvested for the Food Pantry throughout June.

I put plastic on the tents in late March and keep it on until temperatures warm enough and the threat of frost is gone, through May. I put the plastic back on in late September and leave it on until the plants are done.

What's this for?

I don't live where some of my low tents (and hoop house) are. So I need to anticipate conditions and do needed actions in a short visit.

I collected the following data to answer some important questions about growing in the low tents:

  • When do I need to open the tent to the outside environment to avoid baking the plants (given a forecast for clear skies and an expected temperature)?
  • Given a forecast low temperature, what actions do I need to take to avoid frost-killing the plants?

So the exercise described here wasn't an abstract science experiment, but an attempt to find successful growing parameters in the low tents.

I collected temperature (as well as humidity and solar radiation) data outside with a nearby weather station and inside by a Tempo Environmental Monitor inside the tent. I choose readings every 30 minutes for the average temperature during that period.

I collected similar data for the hoop house, but I haven't summarized it in the same way, mainly because during the part of the season I'm growing in the hoop house (May through August) I have less need to guard against freezing, and I don't have much control over high temperatures other than opening doors and rolling up side panels.

Soil temperatures

In November 2015 soil temperature outside the tent was 54 degrees about the same as in late September.

Inside a tent without row cover the soil temperatures was 57 degrees. Soil temperature under the row cover was slightly warmer (after one week) at 58 degrees.

Typical differences

The low tent traps the sun's rays during the day and the temperature inside increases, up to more than 15 degrees in the fall season. On a clear day I would open the tent in early afternoon and then close it around 3:00 to avoid a temperature greater than 90.

The tent's plastic is not insulation so at night the inside temperature is generally only 1 to 2 degrees warmer than outside, except under additional row cover laid over the growing plants.

This graph compares the outside temperature with the temperature inside the tent. Generally the difference is greatest when the sun is shining.

Temperatures over a 28-day period from September through the end of October

Row cover

Over this period a row cover was used in addition to the low tent. This cover close to the ground added from 3 to 7 degrees to the temperature around the plants but only during the night. The cover appeared to retain more of the ground heat than the low tent by itself.

The row cover mitigated the effect of sunlight during the day slightly reducing the warmth around the plants. Notice on the morning of 11/5 the temperature under the cover was 7 degrees warmer than the outside temperature, which was 33 degrees.

Under cover

This graph shows typical temperatures of November weather from sporadic sunshine with rainy, overcast days.

Temperatures over an 8-day period in November

Average difference

During the Fall of 2015 the average outside temperature was 53.9, the average inside temperature was 57.2. That is for every half hour over that time.

With little sun

I had two low tents in the garden that receive all the sunlight that there is - they are not shaded.

At home I had two raised beds that received sunlight for only about 3 to 3 1/2 hours, when the sun shined.

Growth of plants at home was markedly slower than at the garden. I had cabbage in the tent at home and cabbage in the open at the garden. At home the cabbage was spindly and not forming heads after a month, while at the garden they were a bit stockier and just starting to form heads. It is clear, however, that growth with limited sunshine is greatly retarded. (No surprise, but I though maybe the cabbage in the low tent might keep up with those at the garden in the open.

garden/infrastructure/lowtents/temps.txt · Last modified: 2020/06/28 21:12 by davidbac