Notes from the ever-wise, Linda Gilkeson, on how to beat the heat!
After this cool, dim, rainy June leaves of plants are very soft and lush so a sudden change to extremely hot, bright and dry weather will certainly injure soft leaves, fry seedlings and tips of soft shoots. So just be aware of that and provide shade at least in mid-day and do it before the heat wave damages the leaves. After 4 or 5 days of getting used to heat and brighter sunlight, leaves should harden off, but don’t neglect to keep shading and watering tiny seedlings as you sow crops over the next month for next winter’s eating.
After the May heat wave, gardeners saw injury showing up on leaves for weeks afterward so it really pays to be careful right now to avoid damage. See some examples of heat damage of my photo database (scroll down to pg. 175): http://www.lindagilkeson.ca/disorders.html
If you haven’t been mulching so far, this would be the weekend to get that done to keep the soil cooler and retain moisture. Roots will be very close to the surface with all this rain and will be easily fried so will appreciate the insulation of mulch.
Unlike in May, people will now have tomatoes in flower. Tomato pollen is sterilized at temperatures over 32 degrees Celsius (90 degrees F), which means that flowers of plants in greenhouses and tunnels could easily get too hot. Do what you can to cool, ventilate and shade the plants this week, but if you lose some flowers (they just drop off), it will only be those opening during the heat. New blossoms will be OK when the weather cools. To see a photo of heat sterilized tomato flowers scroll down to page 176 on the disorders link (above).