PPDL Picture of the Week
April 16, 2018
Check Soil Temperatures before Planting Cucumbers in a High
Wenjing Guan, Assistant Professor, Department of Horticulture and
Landscape Architecture, Purdue University, Southwest Purdude Agricutural
Growers start to plant tomatoes in
unheated high tunnels around the end of March in southern Indiana. Around that
time, there may still be a few light frosts, or even heavier ones, like the one
we just experienced in the past week. With additional help from row covers
inside of high tunnels, temperatures normally can be maintained above 32°F.
Tomatoes typically do not have problems with the short-term low temperatures.
However, this may not be the case for cucumbers. Although they are both warm
season crops, Cucurbits (cucumbers, cantaloupes, and watermelons) are much more
cold sensitive than Solanaceous crops (tomato, pepper). From a temperature
perspective, this article discusses important considerations for deciding the
time for planting cucumbers in a high tunnel.
The best condition to grow cucumbers
is when soil temperatures are above 70°F. This situation may not happen until
the middle of May inside of the high
tunnels, according to our recorded soil temperatures in high tunnels located in
Vincennes, IN. After the middle of May, there is no doubt that
cucumbers can grow very well, but growers may lose the opportunity to sell
cucumbers with early-season premium prices.
Planting cucumbers before the
middle of May in an unheated high tunnel is reasonable in southern
Indiana. But it is important to be aware of a few important threshold
temperatures. Studies have found that the growth of cucumbers increases
steadily as temperatures increase from 63 to 70°F. Below 63°F, cucumbers
do not grow. In such conditions, plants sit in the soil and become
susceptible to damages caused by pests in the soil. With that said, check soil
temperatures and be sure they are above 63°F before planting cucumbers.
What would happen if cucumbers were
planted with soil temperatures below 60°F? The answer is that you may lose
cucumber seedlings even without pests in the soil. This is because roots of the
young cucumber seedlings lose the function to uptake water under low
temperatures. Without water uptake, plants wilt and eventually die.
This year, we challenged the
cucumbers by planting them in end of March. Wilt was observed following a night
with average soil temperature about 55°F. Soil temperatures continued to drop
to 48°F on the following day that eventually killed all of the cucumber
plants. In another situation, we lost 90% plants following two nights with
average soil temperatures at 58 and 54°F. Checking soil temperatures is not
difficult. Soil thermometers are easy to find at local horticultural supply
shops, and they are not expensive at all. When measuring the soil temperatures,
insert the probe to about 4-6’’ depth and record the temperatures in the
This article was also published on Vegetable Crops Hotline Newsletter (https://vegcropshotline.org/)