Normally, we're all about the tips for gardening in the cold and extending the season. But with a week or more of 90-plus degree temperatures, we decided to investigate the best tips for heatwave gardening. The forecast for the Twin Cities calls for temperatures in the 90s through Thursday—with similar highs throughout the state, with the exception of the North Shore. That will be a full week of above-90 temps in the Twin Cities.
The good news about heatwave gardening is many plants will not need any special care other than a bit more watering. Established trees, shrubs and perennials may look a bit bedraggled, but will be fine. New plantings, annuals (especially those in containers) and vegetables will need more care.
What should a gardener do during a heatwave?
Water Early, Water Deeply
With hot weather—especially if it's windy—plants will be losing moisture through evaporation. To make sure they get the most from your supplemental watering, water early in the day. Watering before the temperatures get really high will guarantee your water goes into the plants, rather than evaporating into the air. Direct the water at the soil and the roots of the plants for maximum hydration. Be sure to water deeply rather than just dampening the soil.
You can help roots stay cool and hydrated by adding compost, grass clippings or a wood chip mulch over the ground. Thickly planted areas—so called living mulches—will also help keep the soil cooler and protect roots.
Don't Worry about Blossom Drop
When the weather gets above 85 degrees in the day or 70 at night, fruiting plants such as tomatoes or peppers may drop their blossoms. This is a survival technique. The plant is focusing on keeping itself going. New blossoms will form as soon as temperatures return to more normal ranges and your crop should not be diminished significantly.
Add Some Shade
Some cool season vegetables may benefit from shade. You can drape shade cloth, row cover or other materials over hoops to keep the vegetables protected. It also helps to harvest what is ready to harvest to take the stress off plants. I harvested a lot of my lettuce as the warm weather hit rather than have it remain in the garden getting bitter.
Care for Containers
Heat is toughest on plants in containers, and many times your annuals will let you know exactly how much they are suffering by wilting up and fainting in their pots. Most containers will need daily watering during times of high heat and small containers or dark colored ones may need watering twice a day. Even when annuals look almost dead, a good watering usually will revive them.
What Not to Do
Your plants are already stressed, so now is not the time for pruning or fertilizing. Pick flowers to enjoy inside (especially all those peonies that opened up over the weekend) but otherwise leave things alone and wait for a cool down.
Here are some additional heat wave gardening techniques from one of our favorite Youtube vegetable gardeners.