Is it too hot to plant veggies? How to help Oregon gardens through hot spring weekend

Spring has been cold, but the heat has finally arrived. Brooke Edmunds, Oregon State University Extension Service community horticulturist, has these tips for seeing your garden through the hot weather expected this weekend.

If forecasts are correct, Portland and Willamette Valley temperatures will have swung from lows in the 40s last weekend to highs in the 90s this weekend. What plants will be stressed by that temperature swing?

New transplants and recently seeded garden beds will most likely be stressed by the heat. New transplants are usually already stressed by the move from a protected greenhouse growing to outdoor living. So, the heat stress will add to that. Transplants don’t have an established root system that extends deep into the soil so can’t take up water as easily.

Also, most hobby greenhouses will overheat and could see temps much higher than the predicted 90′s. That can severely damage plants inside the greenhouse.

What should gardeners focus on this weekend? Priority should be to keep a close eye on all newly transplanted plants or transplants still in their containers. Also, any beds that were newly seeded. Container plantings will also dry out quickly.

If you already put out veggie starts this month, what should you do to help him through the heat?

• Make sure transplants and newly planted seeds stay well-watered. Check every day and water if the soil is dry more than an inch below the surface.
• Add a 1- to 2-inch layer of organic mulch to help keep the soil insulated and hold moisture.
• Use temporary shade cloths to protect transplants from the late afternoon sun. This can be shade cloth fabric purchased from a garden center or even a bedsheet or piece of cardboard.

Will it be too much of a shock to plant tomatoes and other veggie starts this weekend? If not now, when? Next weekend is looking much better for transplanting into the garden. Overcast and highs in the upper 70′s.

Given our wet spring, how much do we need to worry about watering plants through the heat? What’s the best strategy? Focus on 1) newly transplanted and newly seeded beds and 2) plants growing in containers which dry out quicker than in ground. Established landscape plants likely won’t need watering at this point since there is moisture deeper in the soil where their roots are.

Any other advice for gardeners confused by this wacky spring? Luckily, the heat wave is coming early in the season. So, there is still time to replant vegetables if they don’t pull through.

— Oregon State University Extension Service