May is here and we are preparing to plant 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. In 2020, 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. Watching the long-term forecast and having some row covers ready is advisable for early planters.
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° soil. Peppers, cucumbers, melons, and sweet potatoes want at least 60° and eggplants need at least 70°. Planting too early risks seed rotting prior to germination.
You can test soil with a soil thermometer, available at garden shops. Poke the thermometer about 2½ inches into the soil. Since soil temperature will vary throughout the day, a good average is found between 10 and 11 am. It’s good to check the upcoming weather to be sure there isn’t a cold snap on the horizon.
Early 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 summer heat. We are at or near the end of planting time for beets, carrots, broccoli, cabbage, onions, and many greens.
For a detailed list of recommended planting times for vegetables in Hardiness Zones 6a through 8a, check out the Virginia’s Home Garden Vegetable Planting Guide.
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, make note of the good advice in Growing Asparagus in Home Gardens from the University of Minnesota Extension. 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 2⁄3 of the plant below the soil surface. Pull leaves off the bottom 2⁄3 of the plant and either dig the planting hole deep enough to stand the plant up or lay the underground stem section on its side as the illustration demonstrates:
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° temperatures and plenty of water. 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 at the top of the stalk 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. Find more information on VCE publication Sweet Corn.
Keep 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” 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, watch this VCE video.
To control weeds in the garden, destroy them before they develop seeds. Avoid cultivating and hoeing deeply; this can cause damage to shallow rooted vegetables. Also, avoid using mulch or compost that is contaminated with seeds.
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 Garden Shed article “A Fertilization Primer”.
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 save time looking for the main root, and save water as well.
When transplanting seedlings in peat pots, 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, potentially reducing moisture available to plant roots.
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. To absorb moisture, place a desiccant in the container — such as a few layers of paper towels filled with 2 tablespoons of powdered milk and folded up.
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. VCE publication Backyard Composting offers helpful guidance for several composting approaches.
If you are a fruit grower and want to add native plantings to the orchard, 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!
Garden season is in full swing now. Get out there and enjoy it! And let’s talk some more 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/
Featured photo: Strawberries in Bloom. Photo: R Morini
