When it comes to growing vegetables, timing is everything. Peppers planted early, when the soil is still cool, tend to languish, while lettuce seedlings set into the ground too late quickly turn bitter and go to seed prematurely. Learning when to plant the vegetables you like to eat takes a bit of trial and error. Here are a few things to consider as you plant your garden:
IMAGE: Planting lettuce
Find Out Your Last and First Frost Dates. Vegetable crops can be divided broadly into two categories: those that survive frost and those that do not. Common crops that are damaged or outright killed by frost include tomatoes, peppers, eggplant, tomatillos, and squash. It is important to plant these crops after the last frost date in your area. The term last frost refers to the average date in spring when the likelihood that a frost will occur is less than 50% (likewise the term first frost is the date in fall when the likelihood of a frost occurring is more than 50%). Mark that date on your calendar and plan on planting frost sensitive crops at least two weeks after that date. The United States Department of Agriculture (USDA) has a handy searchable map of first and last frost dates.
IMAGE: Measuring soil temperature
Measure Your Soil Temperature. Vegetable roots live in the soil, so it makes sense that the temperature of the soil (not just the air temperature) influences how well they grow. I recommend geeking out and purchasing a simple soil thermometer. This allows you to monitor the temperature of your soil and plant at exactly the right time. Some years the soil warms up slower than others, and that can influence when you should plant. For instance, peas germinate in soil that is 45 degrees F, but I find that they germinate faster and grow stronger when planted out when the soil is at least 50 degrees F. Also, it is important to wait and plant seedlings of warm season crops (like tomatoes and squash) when the soil warms up to 60 degrees F. If you're new to the idea of soil temperature, check out Territorial Seed Company. They include optimal soil temperature information on their seed packs.
Consult a Regional Planting Guide. Seek out regional vegetable gardening resources and books that include planting information for your climate. Ask at your favorite nursery or call your county extension service to see if they can recommend a specific resource for a local planting calendar. For instance, I live in Portland, Oregon, and keep my copy of Seattle Tilth's Maritime Pacific Northwest growing guide close at hand. This month-by-month gardening lays out what to plant when in my climate.
As you plan your planting calendar, don't stress out too much! If you don't plant something at the right time this year, you can always adjust the planting date and try again next year.
Willi Galloway is the author of Grow Cook Eat: A Food Lover’s Guide to Vegetable Gardening, and she writes about organic vegetable gardening and seasonal cooking on her blog, DigginFood.