Let’s talk tomato plants and stress

…and the stress I’m referring to is mostly that of the owner of said tomato plants.

I have been seeing a whole heap of anxiety on social media over the last few weeks around tomato plants and the growers worry about how their plants fair against others. You know, the whole pressure of social media thing. So I thought it might be useful for me to use my little corner of social media to try to help alleviate some of the anxiety out there. Because, whether I had intended it or not, I do seem to be one of the causes for some people. The most common comment on our youtube channel recently has been something around the topic of “my tomato plants are really small compared to yours” or “I’m worried that my tomato plants aren’t doing well, they are so much smaller than EVERYONE else’s”. So I’m going to use one of the positives of blogging to explore this, the positive being that I can go into much more depth on the subject than in videos where the preference is for short-form content. I’ve embedded the video at the bottom of this paragraph for the folk who want to go nosey and see my tomatoes, so everyone should be covered 😀

So let’s chat about my tomatoes, because yes, they are much bigger than most folks’ plants at this time of the year. However, that’s not necessarily a good thing. I started mine very early. Very early – back in January which was a mistake. They have also been grown indoors under grow lights. Now I said it was a mistake to sow my seeds back in January. Simply because very quickly I had huge tomato plants, far too big for the house but it was still too cold to put them out into the garden or to keep them in an unheated greenhouse. Putting them out when the temperatures fall to below 10C can cause problems with their growth – won’t kill them necessarily but can stop their growth or worse, can cause problems. So that’s what I want to chat to you guys about today, because one thing I’ve noticed is that people are focusing on the size of other folks plants and not on how healthy they are. Mine, have a wee issue…

Just a quick note also on the fact that I had tomatoes and peppers growing indoors under lights. The plants were VERY happy and if I could I would have kept things this way as long as possible, however, I wasn’t happy with this setup. I had things set up in my office which meant me working in there with the grow lights running… unfortunately, given my sensitivities to light, things got pretty horrible and I was struggling with horrible headaches and feeling queasy and dizzy. So we had to come up with a solution. But let’s jump to what’s happening now.

How the cold has affected my tomatoes

So I am lucky, my tomatoes are now out in the greenhouse because my greenhouse is heated. Obviously, this isn’t perfect because it costs to heat the greenhouse whereas the house was being heated anyway, but… swings and roundabouts… the greenhouse gets plenty of natural light and the house doesn’t and therefore I had to run lights just for the plants. So heating in the greenhouse, hurrah! Well sort of, I’m trying to keep the heating to a minimum and not just heat the greenhouse up to proper summer temperatures. So I have a thermostat controlling the heater so that the plants are kept at a safe temperature overnight. I don’t heat during the day as the general daylight heats the greenhouse to a suitable temperature. But boy oh boy have I had to rig up a complicated system in there to control things.

Basically, I have a really good, calibrated thermometer which connects to my phone, so I have been using that for the past year to monitor temperatures in there. The downside though is that it doesn’t connect to the heater so I can’t control the heater using that. Instead, I’ve got a digital thermostat that switches the power to the heater on and off as required. Phew…..

But… it turns out that the digital thermostat (fancy pants one designed for plants and the greenhouse) isn’t calibrated properly and doesn’t calibrate. So it was actually 7 degrees different from my proper bluetooth thermometer. And it took me a few weeks to notice, meaning the greenhouse wasn’t at the temperatures I thought it was at night.

So this has meant that the tomato plants and other plants in there were showing signs of stress due to the cold. Now there are a few different signs of stress due to the cold, the most common being cold shock. This is where you get white patches on the leaves of a plant, usually starting at the tips. It’s unsightly but usually, you can take off those leaves and as long as the plant doesn’t experience those cold temperatures again, it will be fine. However, my leaves were showing signs of purple.

What does purple on the plant leaves mean?

So as I said, it wasn’t just my tomato plants that were showing this purpling, which was in its own way a good thing. It meant I could say that the problems weren’t specific to the tomato plants so I could rule out some of the usual culprits of stress like overwatering, under watering, problems with the soil, etc, and instead could be pretty sure the problem was more general to the environment. Luckily I had also research problems with tomato plants in previous seasons so I was aware of colour changes in the leaves and stem and what they could mean.

So purple… what I was finding was happening was that the leaves were changing colour, firstly they were going a very dark green.

Then I noticed the veins in the leaves were going quite purple, followed by a slight purple tinge on the actual leaves themselves which spread from the tips. Finally, the leaves faded and went yellow and eventually died. Obviously, this all happened over the course of a few weeks.

Now, I know for a lot of us, this would instantly be a worry, hence why I wanted to talk about it. Discoloured leaves are generally the tomato plant telling us something is wrong so that we can try to help. It is usually a while before unchecked, the plant will actually die. So in this case, the purple veins and leaf discolouration is a sign that the plant needs phosphorous.

It could be for one of two reasons, firstly, the simplest, maybe the plant needs a feed. Phosphorus is an important element the plant needs, especially once it starts flowering and fruiting. But, it is unlikely that your soil is deficient. Therefore the second cause could be simply that the plants are too cold. This was in fact the issue for me. I have already mentioned the problems with getting my greenhouse temperatures settled, well this is the issue that is causing my plants stress.

So basically, remembering that tomatoes are a warm-weather crop, originating in the much sunnier, warmer climate of Mexico, you can see why a cold April here in Scotland might not be its favourite spot. Tomato plants like to be well above 10C. Now don’t get me wrong, under 10C for a while won’t necessarily kill them, it will just stunt growth and mean you have a slightly sickly plant. They would much prefer to be above 15C and up to 20 – 25C if you can. Especially in terms of ripening the fruit. But if your plant spends any prolonged period below 10C (like in the cold Scottish nights recently), this can actually cause the plant to stop taking up the nutrients from the soil. Hence the lack of phosphorous. There was plenty there, the plant just couldn’t access it because the soil and therefore its roots were too cold.

The good news being that now that I know there was an issue (the plants told me) I can now work to resolve this. So hopefully in a couple of weeks time, I will have some good news about my little tomato plants.