Back in May, I noticed that some of the leaves on my tomato plants were turning yellow. Entire branches were shriveling up and falling off. I knew I was watering my plants plenty, so the leaves weren’t drying up because the plant was thirsty.
It must be a fungus, I thought to myself. When I purchased my seedlings, the salesperson at the garden center had said it was likely to be a cool summer. “Watch out for fungus on your tomatoes,” she said.
I Googled “tomato fungus” when I saw the yellow leaves and identified a likely culprit: early tomato blight. Then I outlined in this post exactly why my plants had early blight. The clincher in my mind was this: The plant leaves started turning yellow right after it had been cool and rainy for three days, which was the perfect environment for fungus to spread.
I pruned my tomatoes of the dying leaves and sprayed fungicide, but nothing seemed to work. I kept watering my tomatoes, but halfway through the summer, I essentially gave up. I was tempted to rip up the plants, but instead I let them be, half-heartedly watering occasionally.
When my zucchini finally kicked the bucket in August, I dug it up to plant something new. I reached deep into the earth to pull out all of the zucchini’s roots, and was shocked to encounter very wet dirt. Not just moist, but muddy. I dug all the way to the bottom of the container and snapped a photo for documentation. It was so wet there was almost standing water. The clouds parted and I had a moment of clarity: All this time, I had been over-watering my tomatoes!
I knew I needed to have drainage holes in my wine barrels; I may be new to the world of container gardening, but I’m not that dense. Clearly, however, there weren’t enough holes. While the dirt was dryer near each hole, even a couple inches away, it was muddy.
When I watered my containers, water also drained out the bottom, and I thought that indicated my barrels were draining properly. Apparently those three drainage holes weren’t sufficient.
Three weeks ago I wrote about the promising new growth on my sad little tomato plant that had been struggling all summer. I welcomed the new shoots but had no idea why they were growing. I know now this new growth coincided with the abandonment of my tomatoes a couple weeks earlier. All they needed was for me to stop actively drowning them and they started to recover. Now new shoots are springing from many different formerly barren branches.
Back when I was drowning my tomatoes, I was checking the moisture in the soil level before watering. I only stuck my finger an inch or two into the soil, however. Tomatoes have deep root systems, and I wasn’t going nearly deep enough. Now I’ll use a skewer to test the moisture level, and water once a week, at most.
It’s counter-intuitive that an over-watered plant’s leaves would turn yellow and fall off. This happens because the mud basically suffocates the plant’s roots, so it can’t take up any water or nutrients. The plant kills off some leaves to keep others healthy.
This experience is a perfect illustration of the dangers of confirmation bias. I never did a thorough examination of why the leaves on my tomato plant were turning yellow. If I had Googled “yellow leaves on tomato plants” I would have seen this page as the No. 1 result. The post emphasizes that yellowing leaves are likely due to watering problems.
Instead, I believed I had a problem with a fungus (hence the search term “tomato fungus” not “yellow leaves on tomato plants”). I found confirmation in my mistaken fungus belief when pictures of early tomato blight pretty closely matched what my tomatoes looked like. It didn’t matter to me that one of my gardening books said early blight “is seldom a problem in containers.” I had my diagnosis, and nothing was going to change my mind.
There is still time for my tomatoes to recover. Plus, I know the first thing I’m doing before planting next year’s tomato crop: Drilling more holes.