Hotcaps are covers used to protect individual plants from suboptimal temperatures. Temperature, solar energy, photosynthetic photon flux (PPF), and tomato (Lycopersicon esculentum Mill.) transplant development were compared for three hotcap designs: 3.8-liter, opaque plastic jugs (PJs); 24-cm-tall wax paper (WP); and Wall-O-Water water-filled plastic teepees (PTs). The average solar energy inside the hotcaps was 57.3%, 67.6%, and 28.9% of full sun at midday and PPF was 44.7%, 49.7%, and 43.8% of full sun at midday for WP, PJs, and PTs, respectively. The rate of temperature decline in a growth chamber was fastest for PJs and slowest for PTs. In the field, air and soil temperatures inside hotcaps were higher than ambient during sunny periods and essentially the same during cloudy weather. The overall mean and mean maximum daily soil and air temperatures for all hotcaps were higher than ambient. PTs had the highest minimum daily soil and air temperatures—2.0 and 1.9C above ambient, respectively. The meantime to first ripe fruit was reduced by 10.7 days for PTs, 6.7 days for WP, and increased by 5 days for PJs compared to noncovered plants. Plants grown under hotcaps weighed less and produced fewer fruit on the first cluster. PJs could not maintain night air temperatures above ambient and were not effective hotcaps.
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