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Are the ‘Dog Days’ of summer taking their toll on your flowers?

The mid-summer malaise can hit plants as the heat rises.  Learn how to help you plant thrive despite the heat.

Contributors: Rick Schoellhorn


If I was sitting in a room with no idea what month it was, I could probably come pretty close to guessing the month simply by the kind of questions we get from gardeners. In late summer gardeners start asking why the magic stopped in their containers and baskets - plants have stopped flowering and are just sitting. Each year we try to diagnose each case as it comes along, but there are some common themes that crop up over and over from one year to the next. Rather than type the same info over and over again, we thought a simple article detailing with the common things to think about might help answer questions and solve problems.

What you often see in the heat of summer, and moving into fall is a combination of factors: soil drying out, fertilizer running out, high temperatures exhausting the plants, and sometimes the accumulation of old flowers, or seed. Each of these things builds up over time and causes the plant stress. For example, each time a plant dries out to the point of wilting, it hardens the plant a little bit, like hardening arteries in people. The stems get thinner, the water has a harder time getting through the thin stems and slowly the plant loses its ability to really power out new flowers and new growth. The same is true when the fertilizer runs out, or the temperatures are extremely high, or the plant starts to set seed… they all cause the plant to lose strength.

Some tips to help your plants cope with the summer doldrums:

  1. Try to make sure plants are always moist (not soggy but never wilting). For many folks, a drip irrigation system can do this and can be set up on a simple timer to water your plants each day. It is simple to install and simplifies your life. This is a tough thing to pull off, but is certainly a worthy goal.
  2. Try increasing your fertilizing frequency as we pass the midway point of summer. Give the plants a little extra food to help them deal with summer temperatures and conditions. A slow release fertilizer is good, but I think the instant energy of a water soluble is even better.
  3. The potting soil by this time of year frequently begins to pull away from the sides of the pot, which is bad news because it means more of your water is running around the outside of the root ball instead of percolating down through it. Thoroughly hydrating the soil can mitigate this issue.  Water your container, wait thirty minutes to give the soil time to soak up water, then water again.  Repeat a few times. Alternately, put six or so inches of water in a tub, sit the container in the tub for a few hours and let it soak up water until the soil is rehydrated.
  4. If things become stressful for the plant it may try to make seed. That seed sucks up a lot of energy and removing it (or deadheading) can really help send more energy into new flowers and new growth. Trim them off with a pair of sharp scissors.

Temperature - obviously depends on where you live, but late summer temperatures can also reduce flowering, most traditional summer annuals do not like temperatures above 90F during the day, or night temperatures much above 60-65F. When temperatures get too high (especially high night temperatures) it makes it very hard for the plant to rest and build up strength and store up any food. If the heat is making you really uncomfortable, many of your plants are likely uncomfortable too. So, each day begins and the plant is working on a food deficit from the day before. In truth, there is little you can do when temperatures get very high, except choose plants that are more heat tolerant, like Luscious® Lantana, and Blue My Mind® Evolvulus. So, if you live in the desert southwest or the deep southeast or if you’d like to see plant suggestions by climate zone – we have suggestions. Choosing plants that are well adapted to your summer conditions is the best way to keep your garden beautiful all summer long.

Pot size: I have moved away from 8-10” diameter hanging baskets. They are the torture chamber of the garden - a tiny pot hanging outside in the wind, being cooked all day by the sun, and not enough soil for the plant roots to find a place to grow all season long. Many times, the roots of the plants have filled the pot when you buy them in spring, where can they go from there? The answer is nowhere. Think about buying larger hanging baskets and then transplanting your smaller pots after you buy them each spring. Be careful that whatever you hang them from is strong enough to hold the weight of the wet basket, nobody wants to pull hooks out of the soffit, or have a large container fall. You should be able to find baskets that are 14, 18, or even 20 inches in diameter. Larger pots with more soil volume won’t dry out so fast, they need less feeding, and they generally do better all season than smaller pots.

Potting soil with fertilizer in it: Potting soil that claims to contain fertilizer, does have fertilizer, BUT it is not enough to last all summer. This initial fertilizer is meant to help a plant become established and doesn’t last much past the first few weeks. We recommend liquid feeding every week, especially if it is raining or you are watering heavily to keep the planters hydrate. The rain (and regular watering) rinse fertilizers from the soil rather quickly. Consider using a slow or controlled release fertilizer since they continuously release fertilizer for a couple months. Proven Winners® slow release fertilizer is excellent and contains extra iron for stronger plants. Osmocote®, Dynamite and Nutricote® are other common brands. Yes, the slow release fertilizers are more expensive, but if you are a lazy gardener (like many of us are!) they make up for it in being so easy to use. Store the fertilizer in a tightly sealed container and put it in a dry place, like a storage shed or cabinet, and the fertilizer will last indefinitely.

Plants are like us. Everything they have been through shapes the way they perform in the future. Few of us can provide the ‘perfect’ environment all of the time, but by making a few changes here and there, we can help our gardens continue to perform through the dog days of summer.

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Anonymous's picture
Anonymous Thu, 08/24/2017 - 8:41am

My plant problem is that they grew TOO LARGE. I have coleus and petunias in three pots, petunias and verbena in another and just petunias in another. They are huge. I've pinched back the coleus all summer long but they are still enormous. And now the petunia stems are too long and are hanging down unattractively. I've been tempted to cut everything back but think it may be too late in the season for them to rejuvenate. Next year I won't fertilize as much I guess. Any ideas?

Kerry Meyer's picture
Kerry Meyer Wed, 10/04/2017 - 3:30pm

Trimming back earlier in the year would help keep the plants under control.  It is pretty late to cut them back at this time. Slowing down on fertilizer would also decrease the rate of growth, but you don't want to completely stop fertilizing.  You calso look for less vigorous plants in the spring as well.  Coleus come in wide range of sizes, so choosing something that doesn't get as big would make maintaning them much easier.  Lastly, you could always consider moving to larger planters, which will better accommodate the larger plants better and make keeping them well watered easier as well!

Anonymous's picture
Anonymous Mon, 08/14/2017 - 12:44pm

As if the heat of summer isn't enough, then come the Japanese beetles. They are still destroying marigolds I have planted in pots!

Sarah Geoghegan's picture
Sarah Geoghegan Tue, 08/15/2017 - 8:34am

You could try Neem Oil on your marigolds for those pesky beetles.
Hope this helps!
Proven Winners

Anonymous's picture
Anonymous Fri, 08/11/2017 - 7:29am

Excellent article and reminder of the basics. Here in Indiana we can see all sorts of summer conditions. This summer started very wet, now is very dry. My plants have not thrived as they normally due, especially the ones in containers. I realize after reading this it's back to basics of appropriate watering and fertilization and perhaps different choices of plants for next season. Thank you!

Anonymous's picture
Anonymous Sat, 08/12/2017 - 7:05am

Great article! We have flowers in pots, baskets & large containers around our clubhouse & by mid July they're looking really sad. This article will be very helpful next Summer when we do this all over again!

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