Give it a Grow: Watermelon & Corn Growing Tips for NM Gardens

Southwest Yard & Garden by Dr. Marisa Thompson

Figure 1. New Mexico growing zones, average number of frost-free days, and average date of last frost. Adapted from Climatological Data, Annual Summary—New Mexico 1982, National Weather Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce.

Question:

Do you have any tips for growing watermelons and corn?

-      Sally C., Albuquerque, NM

Answer:

The best time to plant watermelon seeds or set transplants depends on which part of the state you live in, according to the NMSU Extension Circular 457-B, “Growing Zones, Recommended Crop Varieties, and Planting and Harvesting Information for Home Vegetable Gardens in New Mexico” (http://aces.nmsu.edu/pubs/_circulars/CR457B.pdf). For Albuquerque and other areas with between 150 and 180 frost-free days on average (Figure 1), it is recommended to plant in May. In warmer parts of the state with more than 180 frost-free days each year, like Las Cruces, Roswell, Deming, Carlsbad, and Alamogordo, the watermelon window recommendation is for early April. That doesn’t mean you can’t grow watermelons this year, you’re just starting to push the limits because many watermelons need between 75 and 90 days before they’re ready for harvest, and the average first frost dates in some parts of New Mexico are as early as the end of August.

Knowing the average number of frost-free days and your average last and first frost dates is a significant first step when picking vegetables and specific cultivars (aka “varieties”) that will have enough time to fully ripen during the growing season. By now, the dangers of a late frost are pretty much behind us in all parts of New Mexico. (Knock on wood.) So the worry shifts to when the first fall frost might be, even though it is hard to imagine with temperatures in the 90s across much of the state, and the worst heat yet to come.

Thorough pollination is needed to get corncobs with full kernel set. Sweet corn is wind pollinated, so pollination is enhanced by planting the sweet corn in blocks, rather than one long row so that the plants can easily transfer pollen. Pollination is also reduced during periods of extreme heat. Poor pollination, or drought stress while the kernels are filling out, are the two main causes of poor kernel set in sweet corn.

Days to harvest for sweet corn range from about 60 to 100, depending on the cultivar, but they have a larger recommended planting window than watermelons: May to June in colder parts of the state and late March to July in warmer areas.

Knowing precisely when to harvest is key. For sweet corn, the optimal time to pick is when the silks are brown and dry, the corn grains or kernels are plump, and the liquid inside is milky colored. If the liquid is more watery, it may still be too early. Ripe roasted sweet corn is delicious, so if you can, stagger your corn plantings over a few weeks or plant cultivars with different harvest times so that they aren’t all ready to be picked on the same day.

Many people pick their watermelons too early (including myself). I know how it goes: they get big, and you get nervous and think, “I don’t want it to split or rot!” But after the size maxes out, there is still sweetening up to do. Without accidentally snapping the vine, turn a debatable watermelon over and take a look at the underside that’s been touching the ground. If it’s white, it’s not done yet. Wait until that white area turns to a colorful yellow.

An additional indicator of ripeness is the tightly coiled tendril that grows opposite of the fruit. A bright green and succulent tendril indicates that the fruit is not ripe. A dried, brown tendril suggests the watermelon is ripe, as long as the tendril had not been damaged (Figure 2).

Figure 2. Unripe watermelon with curly, green tendril (photo credit S. Walker).

Lots of other fruits and vegetables grow well in New Mexico. Check out the Extension Circular 457-B, mentioned above, for planting dates of various backyard crops as well as recommended distances between plants, seed depths, and approximate yields. For even more detail, search for Guide H-223, “Home and Market Garden Sweet Corn Production” (http://aces.nmsu.edu/pubs/_h/H223/), revised this March by NMSU Extension Vegetable Specialist Dr. Stephanie Walker. Of course, there are guides available for all sorts of crops. For example, Guide H-231, “Commercial Pumpkin Production for New Mexico” (http://aces.nmsu.edu/pubs/_h/H231/welcome.html), also revised by Dr. Walker, was just released last week.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, Ph.D., is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.