Beating the Heat in your Urban Garden by John

John Reinhardt is an urban planner, writer, photographer, and urban gardener. An avid cook, John is interested in the intersection of urban design, sustainability, and food systems planning. He currently resides in Washington DC and works for the American Planning Association. He currently writes Grown in the City, a blog about urban gardening and food systems planning.

So it’s June already.  If you’ve been following this feature on Thursdays, perhaps you’ve already built yourself self watering planters or planted an herb garden. If you started early, perhaps you’ve even been able to harvest early producers like lettuce, radishes, snow peas, or zucchini.  But now it’s June and it’s getting hot.  Very hot.  This week saw three scorchers and today is no different – and the summer is only beginning.  So it’s fitting that this column focuses on dealing with the heat.

Washington is known for its hot, muggy summers – but how does this influence your gardening?  For starters, it becomes more important to make sure that your plants have enough water.  When plants begin producing fruit, they become water hogs, (most fruits and vegetables are largely water). Since I water from the bottom using self-watering planters, I check for water levels once in the morning. For the past week, I’ve had to add about half a gallon to each planter, each day.  Keep in mind that smaller planters, such as the yogurt container herb planters, will require more frequent watering.

How else might the heat change your plans for a lush, productive garden?  When the temperature rises above 90 degrees, many plants do not tolerate it well.  A whole bunch of things can happen – lettuces, spinach, and herbs can bolt.   Zucchini can drop flowers (which several of mine did, much to my dismay), and tomato pollen can become infertile leading to dry, dead flowers that don’t bear any fruit.

The plants on my balcony are large, because my balcony often gets hotter than the ground temperatures from the reflected sun.  This was great in March and April, when my little seedlings needed the warm temperatures.  Now, it seems like the poor things are baking.  With a week of 90 degree temperatures, I’m a bit worried about a whole round of fruit will not set.  K-State has a great article with more information on “flower drop,” but here’s some quick tips for city dwellers.

1.      If you can, bring the containers inside or put them in the shade.  This doesn’t work for me, as I don’t have a sun room or screen porch.  However, I do have the luxury of moving some of the more heat-sensitive plants into the shade of the shelving unit I put out on my balcony.  The sensitive plants go right to the bottom, where they get the least sun.  The sun lovers, like the lettuce, go on the top shelves.  Because the plants that I keep on the shelving are in small containers, I can move them around if they need more or less sun.

2.      Choose drought tolerant varieties.  For example, Burpee, one of the large seed companies, sells “Heatwave” lettuce, which I am currently using on my balcony.  I sowed this variety a few weeks later than the “gourmet mix”, knowing that it would be hotter when the lettuce matured.  Some varieties of tomatoes and peppers love the heat, as do herbs such as rosemary and oregano, which grow in dry, warm Mediterranean climates.

3.      Pollinate before you have blossom drop, and pinch off any bolting!  If you get to plants such as tomatoes before the heat gets to them, you may be able to pollinate them by hand.  This website has some great information on pollination.  And if you’re growing lettuce, basil, or other leafy vegetable, be sure to pinch off any bolting (when a shoot sticks up and grows flowers).  The bolting of basil may be pretty, but it’s nature’s signal that the plant is in stress or the growing season is coming to a close, and the plant better make seeds to carry on its genes!  Smart, eh?  If you pinch of the stem, however, you can trick the plant into continuing to produce more edible leaves.

If you follow these tips, you can survive a hot DC summer.  Anyone else have any good tips for beating the heat?

12 Comment

  • I always water at night. Despite the risk of appearing to be burgling my own house with a gun (hose nozzle) in hand.

    • You’re feeding the gremlins by watering at night.

      The best time to water is at dawn or early morning so that your plants can thrive and better endure the harsh Summer sun.

      You don’t want to water and nourish the bad guys in your garden both bad bacterial and bad insects. This undesirable growth then has all the night hours to thrive without the sun to dry out.

      Water in the morning.

  • Beating the heat? Yes, a spiked lemonade on a porch. Not for the plants.

  • wow. water in the morning… i did not know that watering at night was a problem. good to know.

  • There’s a trade-off to morning watering. It’s great if you have bottom-watering planters, or if you have time to pour the water directly at the base of each individual plant. However, spraying water over the plants will leave beads of water on the leaves, which will magnify the sunlight and burn the leaves. Do this often enough and you can kill your plants.

    • This is definitely true. I was thinking that most would water with a watering can (do this at the soil level or using a bottom waterer) or with a drip hose. Even if you’re using a spray hose, you can water at the soil level. As WDC mentions, drops on leaves can magnify and cause leaf burn. This is mostly a problem when you water mid-day, when the sun is the hottest though. (People often see a drooping plant, spray it, and end up burning the leaves. If you see a drooping plant, water from the bottom if need be)

  • I just got two new planters for the east-facing front porch. 10″ X 14″ by 30.” They were planters I had been hunting for that many people who’ve lived a long time in the neighborhood have. So I’m excited, but now am planning on putting something in there just as it gets HOT and HUMID here in DC. What I plant will get moderate to high sun exposure there.

    What can I put in there now that won’t croak due to the heat stress? Can I start now and grow anything edible in there over the summer?

  • Nice planters, Andy! Congrats. There’s plenty of things you could still probably grow. Tomatoes, peppers, eggplants, and zucchini would all probably thrive for the next three months. When you do plant, however, do it in the evening after the sun has set – and (although I said always water in the morning), give the soil a nice soaking (not the leaves) right after transplanting. This will give the plant some time to get adjusted. If you transplant in the morning, it’s more likely to go into head shock. Herbs will also do really well.

    Once things get a bit cooler in late August, you can plant lettuce, spinach, snow peas and other cooler-weather crops that will get you through to October!

  • Leaves are a plant’s solar panels.

    Focus and concentrate on the life of your plants’ leaves and you will do well.

    Whether an ornamental or a fruiting plant, in horticulture there is nothing more important than good healthy plentiful green leaves. There are no flowers or subsequent fruit without leaves.

    The refrain, “As right as rain” aptly describes how well your plants respond to rain. Collect some if you can. No irrigation of municipal water is as good as rain.

    I do not subscribe to this long held idea that water droplets on leaves somehow harms a plant. Natural rain has fallen on our plants for time in memorial, they have well survived -and so have we by resulting seasonal harvests !

    Here’s a good text by Linda Yang:

    The City and Town Gardener,
    A Handbook for Planting Small Spaces and Containers

    Random House, 1995.

    So, PoP, where are this year’s pictures of bunched and braided leaves from spent Spring bulbs ?

    • Great points, anonymous. I think most of the “leaf damage” comes when people are spraying things such as miracle grow on the plants in the hot summer sun. This is not a good combination. As you mention, rainwater is best! Ever notice how well the plants look after a thunderstorm, with all that rainwater and nitrogen in the air?

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