Hi John,

Welcome to the Oklahoma Forum, and I hope you'll feel free to pop in and visit anytime. We have a lot of veggie growers here and we're fairly experienced at dealing with both extreme heat and drought.

With regards to your sweet corn issue, the problem is the heat. While drought stress also plays a role, more often than not the failure of crop to properly complete the pollination cycle is linked to heat stress. It is difficult for researchers to study heat stress and drought stress separately in the real world because the two occur together much of the time. Also, for research to be most valid, you have to factor in the moisture levels and those can fluctuate wildly as well. What I have noticed out here in the real world is that if you irrigate heavily you can produce beautiful plants in the heat but you still cannot make them pollinate properly once temperatures hit the upper 90s.

My 2012 early corn, which matured in late May from a late March planting, produced pretty well despite some very hot weather during its growth cycle. My mid-season corn that produced in June produced moderately well, and my late-season corn that "matured" (laughing at myself for using that word because there were almost no ears) in July was a total failure. Well, not totally, I did get two full ears and one half-ear. Most of the late corn plants tasseled in high heat and had no pollen, which was mostly irrelevant because a lot of them didn't even silk, or the silks appeared but failed to elongate. All of these are common summer problems because our summers are always hot, and usually insanely hot. The way we get around those issues here is to plant as early as we can without subjecting the young plants to frost or a late freeze in spring. It also helps to plant a short-season corn that produces fast enough to beat the onset of high heat.

Having said that, in some very hot and dry years, I have gotten a great harvest from an old heirloom variety called Texas Honey June. I got the seed from Southern Exposure Seed Exchange. Thus, I think there likely are a few varieties that tolerate heat better than others, but there's no guarantees. Texas Honey June was my late corn this year and didn't perform well, but in 2009 or 2010 it did produce great in pretty hot weather. In my mind I already had decided that it was too hot for the THJ to produce ears that summer, but then it surprised me and produced very, very well.

With sweet corn, the magic number at which pollination issues seem to occur is roughly 95 degrees. The effect of the heat is magnified if the nighttime temperatures are staying high as well. Then, to add insult to injury, very low relative humidity values makes the issue even worse. You might see a lot more pollination issues, therefore, with hot days, hot nights and low RH values than you would with hot days, cool nights and moderate to high RH values.

When the heat is affecting pollination, you can see the effects in many ways. Sometimes you don't even get tassels, or you get tassels with no pollen or you get tassels and pollen but the pollen is sterile. You sometimes see strange tassels that are malformed, or bizarre silks that look strange and behave even more strangely. Even the silks can be affected. Often, they fail to elongate properly. In some bad drought years, I've seen some corn plants do all of the above and often all at the same time. I don't know why one plant will tassel and another won't, or why one will silk but not tassel or tassel but not silk, but it happens.

I haven't grown popcorn in a long time, but in the years when I grew it, it didn't seem to be affected as badly by the heat as sweet corn is affected.

I rarely even attempt a fall corn crop any more because the heat hangs on far too long most years and it usually is too hot to get good pollination in fall. If I wait late enough in summer for the temperatures to be cool enough for proper pollination, then an early frost or freeze (like we have here this morning) catches the crop and damages it before the ears can mature.

I'm going to link what I consider an excellent description of heat stress-related and drought stress-related corn pollination issues that goes into a great amount of detail.

Is there hope for the plants that haven't yet tasseled or silked? That's a tough one and any answer I offered would be just a guess. Based on my experience here when trying to grow fall corn, I'd say you won't get many ears. Often the heat has had an effect on the plant that causes it to produce sterile pollen or no pollen even on the plants that tassel and silk somewhat later than the main crop.

If you have any more questions, feel free to ask.

Dawn

Here is a link that might be useful: Effect of Heat Stress on Corn Production

Hi Dawn, thanks for all the good information. I'll definitely be planting corn early next year, but also looking for a variety that might handle the fall heat. Right now it's pretty clear that my Kandy Korn is a complete bust, not one tassel looked normal, not one ear (of the few silks that appeared) filled out. You were right about the popcorn, it did slightly better, putting out one normal looking tassel, and a few tassels that were half normal looking. There are a few ears that look like they are filling out, but still a lot of missing silks and strange looking tassels. I'll be happy to get a few ears of Japanese Hulless popcorn, just so I can see if it's really hulless.

This was a particularly long hot late summer and fall, they aren't always like that here...so I'll try again next fall, but maybe with the Texas June Honey.

One other corn question I have...on irrigating: I was watering every other day, sometimes everyday, even when the ground was still damp looking. This goes against my instincts, but the corn seemed to handle it and might even have benefited from all the watering. Is this normal, to water even when the surface is still wet?

John

John,

I wouldn't do it. I'd be afraid of fostering disease, besides the expense of the water. Even when I've had unlimited access to water I have generally watered deeply and then waited to water again until the soil was pretty dry, several inches down. This promotes deeper roots and healthier plants.

George
Tahlequah, OK

Hi John,

You're welcome.

I was afraid your corn would be a bust, based on my experiences in drought years. Maybe next year the weather will be more normal.

I agree with George about the watering. Just because corn will tolerate a lot of moisture, that doesn't mean the moisture is good for it. When corn plants stay too wet, all sorts of disease set in, including some that are fungal in nature.

Like other edible crops with a large water content in the edible portion of the plant that we eat, excessive moisture also can water down the flavor significantly.

I'd give the corn only enough water and not too much, and it may take a few years of growing corn and understanding, first hand and in your own specific soil and climate, exactly how much moisture it needs.

Also, file this tidbit away for future reference in drought years: while you can water heavily to compensate for a lack of raindall, you cannot water enough to make the plants produce ears if the temperatures are too high. All you'll end up with is lush, beautiful green plants that don't produce ears....and a big water bill.

I don't water my corn much at all most years.

More important than watering is planting on time in your region so the plants can grow and then tassel and silk before the temperatures are high enough to impede pollination. My average last frost date is March 28th, and I plant my corn anywhere between March 20th and March 31st most years, depending on the soil temperature and the weather forecast. I don't want to plant it so early that a frost will freeze and kill the young plants as soon as they've sprouted, but I also know that the later I wait to plant, the greater the chance the weather will get too hot too early for good pollination, so I tend to plant earlier rather than later. I also hedge my bets by planting 2 or 3 varieties because sometimes one variety will perform better than another. I always grow "Early Sunglow" as my early variety because it is highly dependable. A planting of Early Sunglow seeded into the ground at the end of March consistently gives me a corn harvest in late-May before the air temperatures get insanely hot in June.

Good luck with next year's crop,

Dawn

Dawn, I've always waited until the weather was warm before I planted corn seeds. If you're planting right after the last frost, what's the minimum soil temperature you look for? The ground must be pretty cold when you plant.

About watering, I didn't start watering a lot until I saw signs of water stress in the corn leaves...and one time I actually had some droopy plants when I didn't water for 4+ days. It seemed that even when the ground looked moist, the plants would sometimes show initial stress signs in the leaves (the leaves look crinkly and have longitudinal striations)...and when I saw that I watered regardless of what the ground looked like. And the plants always picked up after being watered. I tried to water deeply, put down an 1/2-1" of water, let it soak in. I would do this three times. Does that seem like enough water for corn?

John,

LOL. I am the conservative one. At least I wait until just after the last frost date. My best gardening friend who lives just a short distance from me often plants his corn a week before the last frost date, or sometimes in a warm spring, two weeks before.

The soil temperature is what determines if and how quickly the corn seed will sprout. With standard sweet corn (NOT the pickier supersweets) I plant after the soil temperature at planting depth is at or above 50 degrees for at least 3 consecutive days. With the extra-sweet varieties, I wait for 60-70 degree soil.

Our late-winter and spring weather is very erratic here with wild temperature swings all over the place. We occasionally have a very warm winter or early spring day in the 80s or 90s even while we're still having freezing nights. If the soil temperature is in the right range, and there's not a big cold front out there in the 7-10 day forecast models, I can plant easily in March for old-fashioned regular sweet corn, and in April for the newer supersweet hybrids.

I've lost sweet corn to a late freeze only twice since moving here in 1999, and that was before I started using Agribon floating row cover to keep plants warm on an occasional cold night, so I feel like the risk of losing it is relatively small. In both of those years the corn froze, we had an abnormally late freeze/frost in the first week of May in an area where our average last frost date is near the end of March. Planting early is a risk I'll gladly take because often we get so hot so early that I'll have pollination issues with corn planted "late'. The last two summers we've had that kind of heat arrive in May instead of in July, so planting early to beat the heat has become more important to me than ever before.

How much water your sweet corn needs varies a huge amount depending on your soil and how well it holds moisture. Most of my soil is heavy clay (though well-amended with compost in the garden beds) so it holds water a long time. This past summer I grew some in a sandier area and had a really hard time getting it enough water. Of course, we were in the midst of horrendous drought so in that sense, it wasn't a fair test of how well corn would grow in that area in a more normal year. In the drought, the corn planted the earliest performed the best and the corn planted later produced very few ears.

There are times when good moisture is extremely important. The most important time is when the plants are young and small. During the first three weeks or so after the corn plants emerge, it is important that they have good soil moisture to enable them to establish good, strong root systems. The other critical period is the time between the appearance of the tassels and the time you harvest. Once the corn is tasseling, it is critical that it receive adequate moisture so that the ears will be well-filled with nice, filled-out kernels. If the plants are too dry at and after tasseling you can have poorly filled, small ears.

In between those two periods, corn is pretty tough and can handle less moisture.

t lot of this discussion of moisture is relative to what is normal for your area. I live in an area where our average rainfall is about 38-39" a year, with much of that falling in late winter through late spring, and not much of it falling in summer. However, we've had years with less than 18" of rain and years with about 54" of rain. That's another reason early planting is helpful here---it lets you take advantage of this area's rainfall pattern. The last two years we've had about 27" of rain per year, so I've had to water more than usual. If you are in an area that averages 15" ir 20" of rain a year, you'd have to water a lot more in an average year than I do, although if you had good sandy soil that lets great root systems develop, you might not have to water as much as I do if you sand is a sandy loam that holds moisture well.

With corn, just try to keep it pretty moist during those two critical periods, and then try to keep it more or less moist, but not sopping wet, the rest of the time. I have a lot more trouble with my corn in a wet year like 2004 or 2007 than in an average year.

There is no set formula for watering anything. There are too many variables, including how well your soil does or does not hold moisture, how dry or humid your air is, how windy the weather is, etc. You just have to watch the plants and water when they look too dry. Remember, too, that is is always best to water so that the soil is moist 6-8" down. One mistake new gardeners often make is they water briefly---only enough to wet the soil an inch or two beneath the surface--and they water very often. When a person waters shallowly and often, it encourages the plants to form shallow root systems near the soil surface, and these shallow root systems do demand almost daily watering. Plants that have good deep soil moisture send their roots down deeply to reach that moisture and, consequently, they are happy with less frequent irrigation or rainfall. It is much better to water deeply less often so you'll have deeper, healthier root systems on your plants. In a dry year, I try to water my corn once a week to a depth of 6-8" and I use drip irrigation to do so, which keeps the moisture off the foliage. In a wet or even average year, I hardly water the corn at all.

Dawn