Most growing zones begin and end with cooler weather. Sandwiched in the middle is the warm weather of summer. We growers are always looking for ways to push the boundaries of our growing zones to get crops in the ground sooner and extend our harvest into the late fall.
Growing in high tunnels, using heaters, and row cover can help us protect early-season crops. Heck, some may even tolerate a light frost and low temperatures. But tender and extra-tender annual crops have a zero tolerance for temperatures below a certain degree and will perish if they come into contact with frost, even for a short time. Extreme stress during early developmental stages can have lasting negative effects if the crops survive.
Spring can be exciting, and we’re all anxious to start our gardens. If you want to get started early, stick to cold-hardy crops. Here’s a list of nine tender crops you should wait to plant.
Sweetie Pole Cherry Tomatoes
Sweetie Pole Cherry Tomato Seeds
Sugar Baby Watermelons
Sugar Baby Watermelon Seeds
Sweet Bell Blend Sweet Peppers
Sweet Bell Blend Sweet Pepper Seeds
Tomatoes
Starting tomato seeds indoors with proper care and lighting ensures strong seedlings.
I’ll begin with tomatoes because I haven’t met a gardener who doesn’t feature a variety or two in their space. They’re a staple of most homesteads and gardens, and getting the timing right to sow seeds and transplant is crucial to their success. Depending on the variety, type, and growing region, tomato plants take 65 to 90 days to mature, but some can take up to 130 days. ‘Days to maturity’ refers to the date from sowing. Subtract a few weeks from the timeframe for seedlings, given the head start of being started indoors.
I highly recommend starting seeds indoors with heat mats, lots of TLC, and the best lighting you can provide. Slowly harden them off properly on a partly cloudy to cloudy day when outdoor temperatures are safe. Select the healthiest and strongest seedlings to transplant for the best success.
Tomatoes are tropical fruits, born to bask in the summer sun and thrive in the heat. However, be prepared to provide lots of water, support, one to two inches of deep watering per week, and shade cloth as needed. Space plants several feet apart so airflow is ample and disease pressure remains low. Provide support to taller varieties and prune often.
Watermelon
Harvest ripe watermelons when tendrils near the stem turn brown and dry.
April is the perfect time to sow your watermelon seeds in most zones. Since the juicy fruit is cold-sensitive, sow seeds indoors four to six weeks before your last frost date in cell trays or containers about a ½ inch deep and cover with growing medium. Set them on a heat mat in cell trays at around 85°F (29°C), they like it hot. Don’t let the seeds dry out.
Prepare garden beds with lots of well-aged compost or manure. Large watermelon varieties should be spaced six feet apart to vine out and ensure proper nutrients are received. ‘Sugar Baby’, a home gardener favorite, matures quicker and produces smaller fruit but still requires lots of space.
Watermelons can be transplanted from mid to late May through July, zone and region dependent. Soil temperatures should be 70 to 80°F (21 to 27°C). Provide full sun and cover them with insect netting until they flower to protect them from pests that could stunt their growth. Their vigorous vines will create ample shade as they branch out. Fruits will be ready for harvest in 80 to 100 days from sowing. A brown, dried tendril near the stem will indicate a ripe watermelon.
Eggplant
Plant eggplants alongside suitable companions like dill and marigolds.
This versatile summer vegetable thrives in the hottest and driest summers. Popular in Mediterranean and Indian dishes, this nightshade deserves a place in your garden, but don’t plant it too early!
Start eggplant seeds indoors six to eight weeks before your last frost date. Sow them in strip trays or shallow flats and set them atop a heat mat between 80 and 90°F (27 to 32°C).
Keep moisture consistent, but don’t allow the soil to become soggy. Step them up into larger containers until it’s safe to harden them off, about a week before transplanting them. Allow them to acclimate to cooler temperatures, but they won’t appreciate 60°F (16°C) or below. Cold spells will decrease yields and possibly stunt the plants.
Eggplants are heavy feeders, so give them plenty of space and only plant appropriate companions like dill, marigolds, and onions nearby to ensure access to proper nutrients. Ensure the soil is well-draining, and don’t compact around them too much when transplanting. Scout early for pests like the Colorado potato beetle.
Peppers
Optimal germination for peppers requires controlled conditions like a germination chamber.
Peppers are your retired great-aunt Hilda, who loves the beach, has a super dark tan all year, and wears a parka if it’s under 70°F (21°C). Aunt Hilda thrives in heat, and so do peppers! Sow seeds indoors around the same time as your tomatoes or a little after.
Germination rates will be best if you use a germination chamber, humidity dome, or a heat mat. Seeds will sprout in 5 to 21 days, depending on variety and growing conditions. Set the mat between 70 and 95°F (21 and 35°C), ideally around 80°F (27°C). Step peppers up into larger containers when they have at least two sets of true leaves. Allow them to grow indoors under ample light until they’ve been properly introduced to outdoor temperatures and the soil reaches 70°F (21°C). Most sweet peppers will mature in 60 to 90 days, and hot varieties a bit longer.
Did you know the heat of peppers depends on the level of a compound called capsaicin? Capsaicin causes a burning sensation when ingested and it’s present in the membrane down the inside center of each pepper and the seeds. Levels are affected by rise in temperature, plant age, the placement of fruit on the plant, soil conditions, and soil nutrients, among other factors.
Summer Squash and Zucchini
Protect squash and zucchinis from extreme temperatures for optimal growth.
Summer squash and zucchini prefer soil temperatures between 60 and 85°F (16 to 29°C). When transplanted into cold, wet soil, they will experience transplant shock, and growth may be stunted. If you live in a northern region, wait until several weeks until the last anticipated frost date to be safe. Sow seeds indoors on heat mats to improve germination rates. Be gentle when transplanting, as they don’t like their roots messed with.
Plan to protect them from possible cool nighttime lows. They will not tolerate a frost and don’t like temperatures below 65°F (18°C). On the other hand, if you live in a southern region, plant these guys early enough and beat extremely high temperatures, which may cause flowers to abort or fail to produce.
Pro tip: Protect cucurbits with insect netting in anticipation of the first generation of cucumber beetles and squash bugs. If you provide them with food, they’ll stick around all season and wreak havoc.
Sweet Potatoes
Ensure sandy, well-draining soil when planting sweet potatoes successfully.
Sweet potatoes are typically grown from slips which are seedlings farmers and nurseries create from harvested sweet potatoes and sell by the bundle. They include a long root and may or may not have leaves on them. Don’t be alarmed if they look dead, they’re just dormant. Unpack them upon arrival and rehydrate them by placing them into clean water. Plant them as soon as you can, ensuring conditions are ideal.
Their specific temperature and humidity requirements get them a bad rap, but if you’ve ever had a homegrown sweet potato, you’ll agree the extra work is worth it. Northern growers can warm their soil by covering garden beds with black silage tarps for several weeks before transplanting the slips. You can safely do this about four weeks after your last frost date when overnight temperatures exceed 55°F (13°C). Sweet potatoes prefer sandy and well-draining soil that helps them develop a deep, strong root system. Consider raised beds, containers, or fabric grow bags if your soil is rocky or clay-like. Access to full sun is a must. Transplant slips on an overcast day if possible.
Plant the slips deep enough to cover all the roots and let the remaining slip flop over. Nodes will form and strengthen the plant. They’ll look wilted for some time, but don’t worry; it’s all part of the process. Add hoops to the garden bed and cover the slips with a row cover to keep them warm as they get established. Water daily to help roots develop and provide a liquid fertilizer high in phosphorus. They take 90 to 120 days to mature.
Basil
Start germinating basil seeds indoors using heat mats before moving them to warmed soil.
Don’t risk losing the main ingredient for your future pesto and caprese salads by planting it too soon. Basil will not tolerate a frost. Leaves become discolored, and plants suffer greatly when temperatures dip below 40°F (4°C). Basil performs best when outdoor temperatures are around 70°F (21°C).
Start seeds indoors on heat mats four to eight weeks before your last frost and step up as needed until transplant. Allow the soil to warm to at least 50°F (10°C) before transplanting, using a black silage tarp if desired to speed up the process. This delicious herb can be grown in pots, containers, or fabric grow bags.
Consistently prune and harvest basil plants to keep growth healthy, plants strong and bushy, and to prevent bolting. Provide shade when the sun is harsh, or temperatures are over 85°F (29°C). Take advantage of their ability to get along with other garden members.
Sweet Corn
Consider growing sweet corn microgreens for a quick taste of summer.
Humans have been growing sweet corn for thousands of years. Its sweetness, versatility, and humble nature have continued to earn it a spot in our gardens.
When growing corn on a small scale, I recommend transplanting it to decrease the risk of a hungry critter swinging by and eating the seeds you’ve sown. Don’t allow the seedlings to become rootbound, and transplant them within two weeks of sowing. Use the blocking method for the best pollination results.
If you can’t wait for that sweet, juicy flavor, grow sweet corn microgreens for a real treat! They take just a week from sowing to harvest, and it might satisfy your sweet corn cravings while you wait for summer to arrive.
Cucumbers
Germinate cucumber seeds indoors 3 to 4 weeks before transplanting outdoors.
I’m rounding out this list with the ultimate summer vegetable, the cucumber. There are so many to choose from, they are fairly quick to mature and thrive under ideal conditions, and in my opinion, no salad is complete without the sweet, juicy crunch of a cucumber.
Cucumbers germinate and grow into seedlings quickly. Sow seeds indoors three to four weeks before transplanting them outdoors. Germination rates will be best at temperatures between 70 to 85°F (21 to 29°C) and will drop severely below 50°F (10°C). Place them in an area with access to light away from cold, drafty air.
Transplant cucumbers into a hole you’ve created with your hand or a trowel. Fill in the hole and gently tamp it down, careful not to disturb the roots. Deeply water about an inch per week and cover as needed to avoid breakage from wind and rain.
Final Thoughts
Spring is an exciting time in the garden, but don’t rush these popular garden staples. They’ll suffer greatly if they experience cold stress and will not tolerate frost. Waiting a few weeks longer will increase germination rates and yields, decrease disease and pest pressure, and sustain long-term plant health. Happy spring planting!
