Here’s the deal on watering in the heat. So there’s been a heat wave and some inexperienced gardeners see their garden plants wilting and assume it’s a lack of water.
Before you water a wilting plant – put your finger on the soil to see if that soil is damp a few centimeters below the surface!
Plants wilt because they’re losing more moisture than they can pick up from their roots.
If there is adequate soil moisture, adding more isn’t going to make it any easier for the plant to survive, in fact it is only going to make the plant’s job harder. It’s called soil water saturation and this leads to root rot. And more wilting.
If there is adequate soil moisture, the appropriate action is to take a deep breath and allow the plant to recover on its own in the evening. A thick layer of mulch will help the soil temperature stay cool during heat spells and this in turn will keep the plant healthier
This is particularly true of container plants. Always finger-test the soil here before you water, particularly if you see wilting and during periods of high heat.
Overwatering creates root rots and wilting isn’t always a sign of a lack of water in the soil
High nitrate concentrations in vegetables (particularly if the vegetables are subject to low-light conditions, such as in winter greenhouses) pose possible human health risks and are therefore subject to regulatory limits in Europe.
Researchers in Lithuania developed a way to reduce nitrates in leafy vegetables: short-term (three-day, round-the-clock) exposure immediately before harvest by narrow-bandwidth red light provided by light-emitting diodes (LEDs).
LED light before harvest resulted in significantly lower (by 44-65%) nitrate concentrations in lettuce, marjoram, and green onions relative to the concentrations in control vegetables. (under regular high-pressure greenhouse lighting) LED light also boosted carbohydrate concentrations. In some cases, vitamin C concentrations were raised or lowered by LED light.
If you’re growing leafy vegetables in hydroponic conditions during the winter months, it might pay you to add some extra red LED lights for the last three days before harvest.
Reference: Giedre· Samuolene·, et al., “Decrease in Nitrate Concentration in Leafy Vegetables Under a Solid-State Illuminator,” HortScience 44(7), December 2009, 1857-1860. (American Society for Horticultural Science, 113 S. West St., Suite 200, Alexandria, VA 22314-2851.)