It must have been the yellow rose I’d been examining, and then the yellow purslane, followed by a glance at the yellow lilies, because as I pottered about the garden the other day, I found myself singing the words to Mellow Yellow (Donovan from way back). I should point out that I don’t really sing — I simply know the first line to a million songs. Even then, anyone in range would assume they were hearing a coughing goat.
Regardless, as I was pottering and singing, and feeling mellow, it occurred to me that although yellow might be mellow, it sure isn’t when you discover the leaves on a plant have turned that colour overnight. One day they’re a lovely, rich green then one sleep later the jaundice has set in. That’s when the singing stops. In my case it was the lower leaves on a tomato plant in a container on the deck that were fading fast, but why?
I had moved the container the day before and may inadvertently have caused physical damage, but a close examination didn’t reveal any broken stems. Had it only been the odd leaf, I wouldn’t have been concerned, but something was obviously wrong. Yellowing leaves, also known as chlorosis, is a symptom of trouble on any plant, but what was the reason?
As far as tomatoes go, it could be a viral, fungal, or bacterial disease; insect damage, lack of nutrients, lack of water, too much water, sunburn, or possibly, though perhaps not likely, deep rooted psychological problems. The list of possible reasons is so long it really needs a House (popular show) in the garden when it comes to diagnosing a specific cause.
The tomatoes in my raised beds were doing fine; it was just the one container plant that was suffering. I checked over and under the leaves for insects or insect eggs and found nothing, and besides, the problem was spreading upwards from the lower leaves, which made insects the less likely culprit. There were no spots, irregular markings or leaf curling to indicate a disease, so that left an environmental or nutritional reason. I doubted the latter as the plant was in good soil, the same soil as other plants, none of which were suffering.
So was it environmental, specifically the weather, more specifically rain, and lots of it? I’ve been rejoicing in the regular rainfalls we’ve had this spring, but too much and trouble can arise here and there, particularly where there’s poor drainage.
This, I believe was the problem. Because the container was sitting tightly on the deck, the drainage holes were sealed, and with excessive rain this resulted in waterlogged soil. I’ve since set the pot on three or four pebbles (my own advice that I sometimes forget to follow), and I also took a thin twig and carefully poked a few holes into the soil. This improved drainage considerably. I can’t do much about the yellow leaves, other than pull them off, but there shouldn’t be more. Meanwhile, there are lots of tomatoes forming on the plant.
It isn’t easy to diagnose plant problems. If an insect pest is the culprit, they’re usually a little easier to spot, but diseases and ailments caused by nutritional deficiencies are harder to identify. As in humans, prevention is the best policy when it comes to good health. Think of plants as people. Give them a healthy balanced diet, sufficient clean water, and plenty of fresh air. Exercise is essential too, but don’t force a workout on your plants, just spend some mellow time with them.