Help Your Plants Keep Their Cool!

a photo of a water sprinkler in a lawn

By Steffie Littlefield

(This article was first published in The Gateway Gardener August 2007 issue)

a photo of a water sprinkler in a lawnCustomers and clients often ask, “what’s hot this season?”  Well, in St. Louis in August, the weather is what’s HOT!!! So the biggest task during these months is to keep your new plants alive through the “Dog Days of Summer.”

If you already know I’m going to talk about watering you are probably not going to roast your annuals in their pots, have shriveled astilbes or crispy brown hostas.  There is no great mystery to watering–the key is doing it diligently. Ok, so that’s an oversimplification. Yes, there are tricks to good watering and ways to avoid bad watering.

First, we should note that much of the St. Louis area is different than any other gardening area when it comes to watering. We have hot, rainless days, but with so much humidity the ground may stay damp even as the temperatures rise, and it may rain but never soak the ground. If this reality scares you, get a moisture meter because the next worst thing to too little water is too much. If you are new to gardening or St. Louis, use your calendar, note when it rains and how much, keep track of when you watered each section of your garden and when those hydrangeas started to wilt. Please… take your gloves off and feel the soil, use a trowel and check beneath the mulch. If the ground is wet 8” deep and the plant is still wilted 2-3 hours later, turn off the hose, it is over watered.

How much water is enough? The experts advise us that most plants need an inch of rain/water per week. This may not sound like much but it can take hours with a slow soaker hose to get the ground saturated. The good news is, if you did finally get that dry cracked soil wet deeper than 8 inches, it will take days for it to dry out, and in the mean time your garden plants will grow lush and full. The deeper the covering of mulch the longer the ground will retain moisture and the cooler your plant roots will be.

Rotating, impulse or oscillating sprinklers are best for covering large areas of lawn, but waste a lot of water through evaporation, and can also add to disease problems in perennial borders and rose beds. Soaker hoses put the water where it is needed most, in the ground and not in the air. To determine how long to let a soaker hose run, monitor the lowest point and note when water starts to run out of the area. This could take 1-4 hours depending on length of hose and water pressure. In really hot, dry weeks, I will let the water just lightly trickle into my soaker hose over night for a really deep soak.

Heavy clay soils percolate water slowly, so the surface may reach a saturation point before deep soaking occurs, causing wasted water in runoff. If you notice this in your landscape, you may have to water for a shorter period of time, shut the water off for a few hours to allow percolation (water penetrating deeper into the soil), then water again to obtain deep saturation.

When is best time of day to water? Anytime your plants are wilted! Otherwise, morning is really best, especially for lawns. This is when a water meter is helpful, because you can turn it on in the morning and it will automatically shut off when the timer tells it.

Please note that newly planted beds may need more water than established areas, since the soil has been disturbed and may not have settled, making drainage occur faster than in other areas, and water may not be retained as long. Check these new plantings daily when the weather is hot and dry. Container plantings may also need daily watering especially if the pot is smaller than 12” in diameter. Amendments such as Soil Moistâ can help by holding moisture in the soil and making it available to plant roots. If your plants are wilted, slowly apply enough water so that the ground can absorb the water, the plant can take some up and when the plant has revived, the soil is still damp. A watering wand with a rain shower head will make daily watering easier on you and the plants.

Steffie Littlefield is a horticulturist and garden designer at Garden Heights Nursery. She has degrees from St. Louis Community College at Meramec and Southeast Missouri State, and is a member of the Gateway Professional Horticulturist Association.