May 10, 2023: First heat wave alert

From Linda Gilkeson:

As we move into the El Nino weather pattern this summer, here comes the first heat wave of the season. Over this weekend, forecasts show highs of 26-28oC [about 80oF] on Vancouver Island and coastal areas and up to 34oC [93oF] further inland and up the Fraser Valley. Every time I check the long range forecast, it shows higher temperatures! I have sent out heat alerts so many times in the past that I know most of you know the drill, but there are a lot of new gardeners that might need a warning: These temperature would be too hot for tiny seedlings, newly sown seed beds and plants that have been transplanted recently. No matter how well beds are watered, a bare soil surface can get so hot that seedling roots fry because they are close to the surface. Heat waves this early can also damage the new leaves of perennials and overwintered plants because their leaves have been used to cool, moist conditions and leaf cells have not yet adapted to hot weather. SO, start heat proofing your garden right now:

Hold off on new plantings: If you were planning to sow more seeds this weekend, just wait and do it later in cooler weather. Veggie starts in flats might be better off held in deep shade over the weekend rather than being planted out, especially if you don’t have the means to shade them well.

Shade seedbeds: If seeds haven’t come up yet, use burlap, old beach towels, bedsheets or cut open empty compost bags and spread them white side up, over the beds. Check morning and evening for signs of tiny green shoots, at which point, you must remove opaque covers and replace them with shade cloth or other sun screens.

Shade vulnerable plants: Especially important to protect are cool weather crops (peas, lettuce, leafy greens, any young plants in the cabbage family) and newly transplanted starts. Plants with large, soft leaves (squash, beans) could also experience sunscald injury, especially at the highest temperatures. Use horticultural shade cloth (get a fabric that provide 30%-50% shade, but not more) or use wooden or woven latticework covers (cedar lath panels are available at lumber yards). You can turn plastic lattice-work seedling trays upside down over small seedlings. These options let in enough light that you can leave the shade material in place until the heat wave is over. You can also use opaque materials, such as old bed sheets or any kind of lightweight fabric, lace curtains, lace tablecloths. These don’t let in enough light to be left in place for long so if the heat wave goes on more than a couple of days, deploy the covers by mid-morning and uncover plants in late afternoon so they have some time for photosynthesis in the cooler parts of the day. You can use floating row cover by folding it over several times to make it more opaque and propping it up on stakes so there is good air circulation under it (it was designed to trap heat so don’t cover plants tightly with it) . If you have installed floating row cover or insect netting over carrot and cabbage family seed beds to protect again root fly attack, leave the cover in place and lay shade cloth, curtain material, etc. on top of the insect cover.

Protect plants in greenhouses: Temperatures likely will get far too high without shading so cover greenhouses and tunnels with shade cloth. If that isn’t possible, then shade the plants inside the greenhouse using any kind of shading you can devise. Open vents and doors wide, increase ventilation, use high speed fans to dump heat.

Mulch as much as possible: Spread mulch right now on established plants, such as peas, cabbage family, new strawberry plants, onion seedlings. Mulch plants in greenhouses, too.

AND don’t forget to water: Most of us haven’t been thinking about irrigation yet, so don’t forget to check the soil for moisture and keep plants watered accordingly.

Harvest before the heat: Overwintered spinach, cauliflower, purple sprouting broccoli and other plants are quickly shooting up and this heat will accelerate that. For best quality you might want to harvest before the weekend. The last of my winter cauliflowers are nearly ready so I will cut them before heat causes the curds to separate and lose the sweet, mild flavour.

For more detail, see info in last month’s message (April 21) and my June 24, 2021: Linda Gilkeson || West Coast Gardening || Gardening Tips

Republished with permission from Linda Gilkeson’s Gardening Tips. See Linda’s website to sign up for her newsletter, purchase books, access free presentations and identify pests and diseases which may affect West Coast gardens.