May is here and we are starting to think about planting summer vegetables. Eager planters enter the lottery of predicting the last frost. Here in hardiness zone 7a, average last frost date is April 15-25. “Average” is the operative word. Take last year for example. After a warm winter and spring we had a couple of surprise frosts in the second week of May, requiring us to scurry around and cover early tomato transplants. Keeping an eye on the long-term forecast is definitely advisable, given the weather variability in our region.
In fact, soil temperature is equally critical for reliable seed germination and transplant health. Cool-weather crops like spinach, lettuce, greens, peas, onions, and root crops need soil temperatures in the 35-40 degree range. Actually, 80 degrees is the optimum temperature for germination but these crops don’t grow well in the heat, so we compromise. Starting seeds indoors and transplanting all except root vegetables (which don’t transplant well) is the most efficient practice.
Warm-weather crops including tomatoes, corn, and beans need at least 55-degree soil. Peppers, cucumbers, melons, and sweet potatoes want at least 60 degrees and eggplants need at least 70 degrees. Planting too early risks seed rotting prior to germination as well.
You can test soil with a soil thermometer, available at most garden shops. Poke the thermometer about 2 ½ inches into the soil. Since soil temperature will vary throughout the day and night, a good average is found between 10 and 11 am. Again, it’s good to check the upcoming weather to be sure there isn’t a cold snap on the horizon.
Eager planters may already be harvesting radishes, peas, and a variety of greens. Good for you! Planting cool-weather vegetables now requires looking at days to maturity. There’s no sense starting crops now that won’t tolerate the warmer weather of summer. We are at or near the end of planting time for beets, carrots, broccoli, cabbage, onions, and many greens intolerant of heat.
For a detailed list of recommended planting times for vegetables in Hardiness Zones 6 and 7, check out Extension Publication 426-331, Vegetable Planting Guide and Recommended Planting Dates.
If you have a mature asparagus patch, you are likely harvesting fresh spears now. If want to start to grow asparagus, it’s too late to plant this year. To be sure you get it right next year, check out the good advice in Growing Asparagus in Home Gardens from the University of Minnesota Extension and make a note for next year. Keep in mind that the Virginia Piedmont is about 2-3 weeks ahead of Minnesota for planting and harvesting, but the rest of the advice is right on.
Other tips for May vegetable gardening in our area:
Tomato transplants are ready to be placed in the garden when they have 5-7 leaves. When transplanting tomatoes, place two-thirds of the plant below the soil surface. Pull leaves off the bottom two-thirds of the plants and either dig the planting hole deep enough to stand the plant up or lay the underground stem section on its side. Tomatoes will add roots underground and build a stronger root system if planted this way. When choosing your tomato varieties consider determinate types that ripen within a narrow time period if you are a canner and want a single harvest. Indeterminate varieties will provide a steady supply of ripening fruits until frost, if well cared for.
Eggplants like 80 to 90 degree temperatures and plenty of water. It’s best to water them thoroughly twice a week during dry periods.
Speaking of moisture, beans, peas, and other legumes that fix soil nitrogen produce fewer, smaller root nodules when water stressed. It is important to keep them well-watered.
Extend your harvest season by planting sweet corn and beans every two weeks through the end of June. An alternative with corn is to plant early-, mid-, and late-maturing varieties at the same time.
Missing corn kernels on your corn ears? This may be the result of poor pollination. Sweet corn is wind-pollinated. Pollen from the corn flower has to reach every strand of silk on each growing ear to develop fully-kernelled mature corn ears. Block planting in short rows (3-4 rows or more) will pollinate more successfully than 1 or 2 long rows. For more information on growing sweet corn, take a look at Virginia Cooperative Extension Publication 426-405.
Keep your potatoes covered. The skins of potatoes exposed to sunlight will turn green. This green color comes from the pigment chlorophyll which is produced as a response to sunlight. “Green Potatoes” will often develop a bitter taste and may even become toxic. This can be prevented by covering the exposed potatoes by hilling-up dirt over them or covering them with straw mulch. For additional information on growing potatoes, see Virginia Cooperative Extension Publication 426-413.
To control weeds in the garden, destroy them before they develop seeds. Refrain from cultivating and hoeing deeply; this can cause damage to the shallow roots of your vegetables. Also, avoid using mulch or compost contaminated with seeds. For additional information on controlling weeds in the home garden, see Virginia Cooperative Extension Publication 426-364.
Fertilization is an important element in maximizing garden output. There are problems with over- and under-fertilizing, different impacts from synthetic and natural fertilizers, and soil health issues to consider. If you would benefit from more insight into fertilizer use, check out the article “A Fertilization Primer” in the April 2021 Garden Shed.
When watermelons, muskmelons, squash, and cucumbers are planted in a hill, place a stick upright in the middle of the hill and leave it there. Later in the summer when the hill becomes hidden by the vines, you will know where to water. You’ll not only save time looking for the main root, but you’ll save water as well.
When transplanting seedlings in peat pots, gently tear off the top inch of the pot; the upper edges of the pot should be covered with soil to avoid wicking water away from the soil surface. Wicking may reduce the amount of moisture available to the roots of the plant.
If you are growing Cole crops, including cabbage, broccoli, cauliflower, kale, collards, or other greens, May will likely bring a variety of cabbage worms that can decimate your crop. Options for control include hand-picking, using an organic pesticide like Bt (Bacillus thuringiensis), or row covers. I have also had luck hanging decoys of cabbage moths above that area of the garden. The decoys appear to discourage territorial moths from laying their eggs in that location. For more information check out Garden Shed articles “OMG What’s Eating the Broccoli” and “Row Covers: a Gardening Season Extender with Benefits”. If you choose to try the non-chemical row cover technique, act quickly to get them in place before the cabbage moths arrive.
To preserve leftover seeds, store them in a sealed container and refrigerate them. Place a desiccant, such as a few layers of paper towels with 2 tablespoons of powdered milk folded up, inside the container to absorb moisture.
R Morini
This is also a great time to start a fresh batch of compost. The warm temperatures will speed up decomposition if you keep the pile moist and aerated. Grass clippings and kitchen scraps become available as we begin mowing lawns and eating seasonal fruits and vegetables. If you’ve saved some leaves from last fall, you have what you need to create a good compost batch that will be ready for use this fall. Refer to Garden Shed article “Backyard Composting with Practical Tips from the Pros” for more details on composting.
If you are a fruit grower and want to add native plantings at the same time, give pawpaws a try. There is good advice for growing and eating pawpaws in the Garden Shed articles “Pawpaws: Resilient and Delectable Natives” and “Yummy Recipes With Pawpaws.” Go native!
An ironic benefit of COVID restrictions has been a surge in edible gardening interest, for reasons ranging from food insecurity to relaxation. Let’s hope those who started gardening in the past year have good luck and stay safe. Thanks for checking in and we will see you next month!
Resources:
“Vegetable Planting Guide and Recommended Planting Dates.” Va. Coop. Ext. Publication No. 426-331, http://pubs.ext.vt.edu/426/426-331/426-331.html
“Sweet Corn,” Va. Coop. Ext. Publication No. 426-405, http://pubs.ext.vt.edu/426/426-405/426-405.html
VA Cooperative Extension: May Tips: Vegetables https://albemarle.ext.vt.edu/content/dam/albemarle_ext_vt_edu/files/hort-tip-sheets/5-14-veg.pdf
Soil Temperatures by Vegetable, K-State Extension: https://enewsletters.k-state.edu/postrockdistrictfcs/2021/02/23/soil-temperatures-and-vegetables/
Cover photo: “Spring 2009” by sshreeves is licensed under CC BY 2.0
