Is it Bad to Water Plants On a Hot Day? + When is a Bed Dead?

Episode Overview

• In this "Thurrapy" session, Farmer Jesse answers Patreon questions about managing frost-damaged crops and the nuances of watering during hot weather.
• The episode explores the difficult decision of when to pull damaged crops versus waiting for recovery, highlighting the tension between potential yield and efficient use of farm space.
• Jesse delves into the physiological reasons why watering in the heat of the day can be less effective, offering strategies to optimize plant health and water use.
• The discussion includes a look at "buttoning up" in brassicas after a frost and practical advice for filling gaps in direct-seeded beds.

Key Concepts

• Managing Frost Damage: When crops like cauliflower or broccoli suffer severe frost damage, they often "button up," meaning they recover but only produce very small, unmarketable heads. In market gardening, it's often a better business decision to pull severely damaged plants and replant with a quicker, more reliable crop rather than wait for a subpar harvest.
• Filling Gaps in Beds: Spotty germination or minor crop loss shouldn't always result in scrapping an entire bed. Having quick-growing "filler" crops on hand (like lettuce heads, scallions, or radishes in trays) allows farmers to plug gaps and maintain the productivity of the bed space without starting over completely.
• Watering in the Heat: The common advice to avoid watering in the heat of the day is partly about evaporation and waste, but also about plant physiology. When plants are extremely hot, the Rubisco enzyme often stops fixing carbon (in C3 plants), meaning the plant isn't effectively photosynthesizing or utilizing the water applied to the soil.
• Cooling the Plant System: To improve water uptake and photosynthesis during hot weather, it's more effective to cool the plants and the soil. This is why watering in the morning or evening is preferred, and why misting or using shade cloth can help lower the plant's temperature, allowing it to function and utilize water more efficiently.

Quotes

• At 3:28 - "When broccoli/cauliflower get hit that hard with a frost, they will often do what we call buttoning up, meaning that they may recover and grow fine, but then make a very tiny head." - Explaining the physiological response of brassicas to severe stress and why patience might not yield a marketable crop.
• At 4:50 - "When it does happen, I like to have like a lettuce head tray or green onion tray or something on hand to fill the gaps... That way I'm not losing three quarters of a bed of carrots." - Providing a practical strategy for maximizing bed space and mitigating losses from spotty germination or minor damage.
• At 10:48 - "If plants are hot, they won't be utilizing any water that you put on the soil really well because the Rubisco enzyme tends to stop fixing carbon in C3 plants... In other words, photosynthesis slows down when it's super hot." - Clarifying the biological reason why watering hot soil isn't always effective, moving beyond just the issue of evaporation.

Takeaways

• When deciding whether to pull a damaged crop, assess the likelihood of a profitable yield; if it's low (like buttoning brassicas), cut your losses and replant with a fast-growing alternative.
• Keep trays of quick, adaptable transplants (like lettuce or scallions) ready to fill gaps in direct-seeded beds, ensuring you maximize the productivity of your garden space.
• Optimize watering during hot weather by watering in the cooler morning or evening hours to ensure plants are physiologically able to utilize the moisture.
• If you must water during extreme heat, consider misting to cool the plant foliage or using shade cloth, rather than just soaking the hot soil.