Photo by Erica Browne Grivas:: Lettuces are a perfect crop to plant in the chilly spring. These at the Bellevue Botanical Garden are being protected from deer.
Photo by Erica Browne Grivas:: Lettuces are a perfect crop to plant in the chilly spring. These at the Bellevue Botanical Garden are being protected from deer.

You’ve likely heard the adage, “right plant, right place.” It is probably gardening’s golden rule. If you don’t match the plants’ needs for soil, sun, and moisture conditions, it just won’t thrive. 

A corollary, or subset of that rule because it’s really the same concept, just not often talked about, is planting at the right time for a specific plant.

If you’ve gardened for a bit, you’ve noticed that plants follow their own time clock, not ours. Sometimes, they get tricked by unexpected weather blips, but usually their internal barometers know better than we do.

Peas like cool weather, we are told, but if you plant them too early, when the ground is saturated, they may rot before they can germinate. “Plant peas on Saint Patrick’s Day” may be a good rule of thumb where you garden, but it may not.

Some seeds and plants, like many half-hardy annuals such as poppies and calendula, can overwinter in our chilly, wet soil, but plants that like it warmer would rather have a toasty soil bed to slip into before growing.

So, what’s the answer? If there is a plant you really want to grow, you may need to become a weather detective. Start noticing the microclimates in your yard.

I have dahlias and daffodils all over, but they come up first where the soil warms up fastest, often in front of a heat-reflecting wall. Do your research, pore over the seed packet instructions, and check them against the real-time conditions happening in your yard. For instance, tomatoes. Yes, it always comes back to tomatoes with me. But as they are America’s favorite crop, and as we are past Mother’s Day (another one of those axiomatic rules), Seattleites are itching to plant, so it makes sense to discuss them. Tomatoes like the air temperature to be regularly over 55 degrees Fahrenheit — even at night — and over 60 in the soil. 

First, our evening temps have been in the low 40s, and even our daytime highs were barely passing 50 degrees during the week leading up to Mother’s Day.

For more data, I bought a soil thermometer this year, which looks identical to a candy thermometer I bought for making Insta-Pot yogurt, but I haven’t compared the readings. In any case, if it is correct, my soil is warmer than expected. I also learned my raised bed, which is “supposed” to warm up the fastest, wasn’t appreciably higher than my warmest areas. Last weekend, temperatures throughout my yard were hovering around 60 degrees, while they were more like 47 a month ago.

Because of the air temperatures, though, I’m still babying my seedlings and starts in the house under lights and likely will plant around the first week of June. Even then I’ll probably add some external temperature control in the form of season extenders (marketed as “Wall o’ Waters”) or frost-cloth fabric wrapped around the tomato cages.

The reason for that timing is you want to allow a week or so to “harden off” or acclimate your indoor plants transitioning outside. This goes for the florist hydrangea or jasmine you were gifted or your houseplants you’d like to give a summer vacation.

Fear not — you can plant tomatoes here through mid-June and still get a great harvest if you choose varieties that mature within 55 to 75 days.

If you have a raised bed or open space, you can give that soil a head start by covering in plastic — clear, red or black — for the next couple of weeks. Another idea is surrounding plants with milk jugs filled with water, or bricks or rocks, which act as heat storage overnight.

Other annual plants that like it hotter than we’ve got it right now are squash, beans, eggplant, peppers, melon, sunflowers and zinnias. This is still a perfect time to plant cooler crops like peas, potatoes, lettuce, beets, spinach and kale.