Some Like it Hot; Most Plants Do NOT!
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Q. With rain being scarce and the city rationing water, I'm hoping you can help me select some drought resistant veggie varieties. Last summer especially, it seemed like the soil moisture was just steaming away, so I would also appreciate any watering tips. And do I need to partially shade plants that would normally be considered "full sun"?
---Brianne in Oklahoma City
---Jan in Oklahoma City
The last two seasons, it seems we've had about two weeks of Spring and then brutally hot Summer weather until Thanksgiving. Are there vegetables that can survive our hot long Summers? Thanks; love your show!
---Sam in Oklahoma City
A. If current global trends continue, more and more gardeners will face similar problems in seasons to come—so folks who have suffered through any unusually long hot, dry spells in the past will want to play close attention, regardless of where they live. Many of the tricks and techniques I'm about to describe will benefit them as well.
Now, I looked up the average monthly temperatures for the Oklahoma City area, and Sam is correct; but Spring is always going to be brief where the AVERAGE daytime high in March is in the 60's. And, unfortunately, the numbers also say that July and August days are always going to average in the mid-90's—meaning that the pollen of temperature sensitive crops like tomatoes, peppers and sweet corn should be expected to fry for those 60 days. (At least with most varieties of those crops; more on this in a bit.) So while for some of us, this kind of weather is 'the new normal' (like me in PA who just gardened through the hottest summer in our recorded history), it's also the old normal for our OK listeners.
So growers in predictably hot climes might want to treat July and August like Northerners treat January and February. And you can—your warm Springs allow you to put plants in the ground a month or two ahead of a Pennsylvania gardener. Put good sized plants of short season (60 to 80 day) tomatoes outside on say, April 1st, and you'll have 90 days of ideal growing time before the Gates of Hell open up. Same thing on the back end—put out good sized plants around September 1st and you'll get another 90 days or close to it.
And you can extend both those seasons deeper into the middle with a trick that professionals use—shade cloth. Yes, shade—we often think of a lot of our summer plants as 'full sun', but that expression means different things in New England and New Mexico. In a Northern climate it often means what it says, but in predictably hot, hot, hot places it means "get me out of this full sun after 2 pm or I'll burn to a crisp!"
It's always a good idea to locate a hot climate garden in a spot that gets afternoon shade; but if you can't do that, consider building a hoop house-like frame structure that you can run shade cloth over. The specialized fabric provides a surprising amount of solar reprieve.
I would also advise everyone who gardens where water is scarce to invest heavily in rain barrels—or even cisterns if you grow on a large scale. Oklahoma tends to get the most rain in May and June, so collecting gutter water then could easily spell the difference between a Garden of Eatin' and a depressing shot in a Ken Burns documentary in August. Elevate these as high as possible, so that gravity will feed the water to your plants. And be sure that they're screened against mosquito breeding and/or add BTI to the water on a regular basis to prevent such breeding.
You should investigate grey water systems as well; wherever legally possible, you should attempt to re-use your shower, tub and even washing machine drain water. (See this previous Question of the Week for more grey details.) Harvested or grey, feed the water into drip irrigation lines. Covered with mulch to prevent evaporation, drip lines are the most efficient way to water.
And there should always be a two inch layer of mulch on the soil surface to keep moisture in the ground. (See this previous Question of the Week on mulching choices.) Early morning is always the best time to water. And always water at the base of the plants. In hot and dry climes, the air eats up half the water from an impact sprinkler; and in hot and humid areas (Hello, St Louis!), overhead watering makes disease woes much worse. (See this previous Q of the Week for lots more 'wise watering' advice.)
I'll add that a 1993 ORGANIC GARDENING magazine story found that all cherry tomatoes do well in the heat. For full sized fruits, hot weather growers were urged to try the "heat set" tomatoes, like Solar Set, Heatwave and Surefire—all bred to produce viable pollen in hot temperatures.