I’ve been getting quite a few questions this last week or three about why container plants are dying in some areas. And what folks can do about it. I do have a simple solution so…
Let Me Start With Heat
This is a problem in the garden to be sure from two points of view: the first is leaf temperature and the second is soil temperature. When leaf temperatures get over 83F (28.3C) leaf transpiration (leaf activity) pretty much stops.
Some plants have higher thresholds and some lower but generally speaking, the hotter it gets the less energy a leaf is going to produce during the day. The plant produces energy during the day and grows during the night so if daytime energy production is reduced, night time growth and development is reduced.
It’s a bit tougher to identify soil temperature thresholds although last year was clear they’re going on. I talked to more than one nurseryman who had reduced crops and growth because the soil temperatures in both the ground grown crops and the pot crops was simply too high.
So let’s simply say when soil gets too hot, plants don’t do well.
The Myth of Watering To Cool
There’s some mythology out there that says you can water to cool down your plants. Well, you can mist water over the leaves to cool them down (we used to do that in the greenhouse) but that’s a short lived thing (like a few minutes unless you repeat regularly) but watering a plant’s soil isn’t going to cool down the leaves. It may cool the soil short-term but here’s the problem.
If you overwater trying to cool a plant down, you’ll rot it out instead. Water when the pot soil is dry, not before. It’s a tricky balancing act when there’s a lot of heat and you’re trying to grow heat sensitive plants.
Why Are My Container Plants Dying?
That’s what I’m hearing about now- why isn’t my tomato growing? Why is it dying? Why are my container plants dying?
- The air temperature is too hot.
- The soil temperature is too hot.
- There’s too much water being applied.
- Way too much stress on the plant.
- The solution to this is shade.
Simply move your container plants out of that hot midday sun.
You’re SOL if your plants are in a garden unless you install a shade cover. (see below for resource)
Southern gardeners know they can put Northern full sun plants in the shade and they’ll get a decent plant. But Northern gardeners don’t know this yet – and we don’t have enough experience at these hot summers yet (but we will as this trend continues) to adjust our plantings.
Bottom line – you have to figure out a way to reduce leaf temperatures and/or soil temperatures if you want decent growth. Figure out a way to shade those plants a bit if they’re in the soil or move containers to slightly less brutal spots.
But there’s nothing you can add to the soil or to the plants to fix excessive heat although I’m hearing a lot of you are trying. I’m not going to list what you’ve used this week but let me say no additive to the soil or plant is going to fight too high heat.
A Second Related Issue
And yes, sorry to say but this is going to lead to all manner of tomato fruiting problems. A variable soil water problem is going to lead to excessive blossom end rot and no – epsom salts or calcium additions aren’t going to solve this no matter how many times you read it.
The variability in water and temperature swings are the issue.
If this keeps up in main harvest season, we’re going to see a lot of cracked tomatoes and insects such as earwigs and ants taking advantage of the cracks to get moisture – the problem again isn’t controlling earwigs (they are major garden predator good guys) or ants but rather the temperature and watering issues.
It’s not soil – it’s cultural.
So you fix the culture (air and soil temperature) and you fix the problem.
Get some shade. Move containers out of the brutal sun. Build it, get shade fabric, put umbrellas over small plots, do whatever it takes if you want to reduce that leaf temperature.
If you need more container gardening ideas, click here
Welcome to Southern summers.
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As An Aside For Cold Springs
Overwatering in cold seasons does pretty much the same thing – puts stress on the plant. The plant will slow down growth (because of the cold temperatures) and also the overwatering puts stress on the plants.