Tomato Red Face: Photosynthesis Fail

When I started this blog, I figured I was a better-than-average tomato grower. I’d picked up a lot of tricks over the years, I said. I also said that tomatoes are super resilient and hard to ruin – which is kind of true. You can do a lot of things wrong and still get some tomatoes, but they may not be very good tomatoes, or the plants may not produce to their full potential – and it’s pretty clear that this is what happened to me this summer.

As I mentioned I’ve been taking some classes through the U of S’s Prairie Horticulture Certificate program and having multiple “eureka” moments about what I may have screwed up this summer, usually based on common but bad advice. While this is embarrassing for me, someone who thought they were so good at growing tomatoes that I could have a whole blog about it, I owe it to you, my 11 or so readers, to talk about the practices I used that were not based in sound science. These posts focus on four specific topics I didn’t understand very well (photosynthesis, plant hormones, nutrient uptake, root development) and why my well-intentioned but misguided practices may have led to my 2020 gardening woes.

Regarding sources – unless otherwise specified, the majority of general plant science information in these posts is based on what I learned in the University of Saskatchewan Prairie Horticulture Certificate courses HORT 13 Applied Botany and SLSC 14 Soils for Horticulture.

I may be most embarrassed about this one, but simple Google searches on the subject turn up so much conflicting and downright incorrect advice that I suppose I need not be. I mentioned having issues with tomato flavour this year, and while I can’t diagnose the cause for certain, I can talk about how some of the practices I employed near the end of the season probably didn’t help.

We all remember our photosynthesis unit from middle school science, right? Plants! Green! Sunlight! We can easily recall the flash card vocabulary, but what about the actual science? Having not taken a biology class since high school, it’s safe to say I didn’t understand how to apply this incredibly important concept to the plants I was growing.

Photosynthesis is simply a chemical reaction performed by plants, which takes carbon dioxide and water and turns them into sugar (technically glucose), water, and oxygen. The sugar is food the plant needs to grow; it also gets stored in the plant’s fruit (making the fruit delicious ensures animals will eat it and spread the seeds). This process CANNOT take place without light, which plants absorb through their green parts. This does not mean the plant is absorbing green light – again, go back to Grade 7 science, and recall that if you’re seeing a colour, that object is actually reflecting said colour back at you. Plants absorb red and blue light, the wavelengths that power photosynthesis, through their green leaves. Plants cannot make sugar without proper light.

If you have been reading this blog all summer, you are probably beginning to recognize where I inadvertently limited my tomatoes’ ability to perform photosynthesis.

If photosynthesis is what makes sugar, then photosynthesis is critical for ensuring our tomatoes have good flavour. In order to try and “speed up” my immature August tomatoes, I did two very dumb things: I covered them up in red plastic, and cut off a bunch of the green parts (i.e. leaves).

The only photo I have of this plastic is from the beginning of the season – you may recall I noticed the plants struggling and removed it, but assumed that late season plants didn’t need light so it was safe to use in August.

Gimmicky products abound for how to “hack” sunlight for better plant growth, but the biggest “duh” moment I had in my Applied Botany class was realizing that if a plant needs direct sun, the best way to ensure it gets direct sun is… give it direct sun. There is simply no need to try and to filter specific wavelengths or bend the light underneath the leaves or whatever the salesperson wants to tell you. The best light for tomatoes, which are a plant that requires copious amounts of direct sun, is definitely not light that has been filtered through red plastic (which would actually be reflecting some of the red wavelengths AWAY from the plant, as well as creating shade).

So not only did I block my plants’ access to direct sunlight when they needed to be making delicious sugar… I also further limited their ability to absorb the light that did get through the plastic by cutting off some of the largest leaves. Because “they weren’t doing anything” and “the plant needed to put its energy into growing fruit.” Insert facepalm emoji.

Just like people, plants need food for energy! They can’t make their food (sugar) without photosynthesis! They can’t do photosynthesis without absorbing light on their green parts. Let the stupidity of my actions, and my audacity for having an actual blog about tomatoes when I thought these were good ideas, wash over you.

But wait – sugar is plant food? Then what do we bother fertilizing for, if photosynthesis does all the work to feed the plant? Fertilizer is still necessary, because it provides essential nutrients for the plant – but nutrients are not food. To continue the “just like people” analogy, you and I cannot survive on vitamins and minerals alone – we need calories. Plants do make all their own food, but they don’t conjure their own vitamins and minerals in the process. While people can efficiently take in nutrients via our food, plants don’t work this way, which is why they need to take up nutrients through their roots.

Hopefully we’re now pretty clear on what NOT to do to try and make tomatoes grow or ripen faster. The question remains – is there anything you can do if your tomatoes are super late? Stay tuned!

While I’m not proud of any of this, I’m excited to be able to learn from these mistakes. I’m writing this down for myself a) (of course) to fulfill the requirements of my Applied Botany class but also b) so I can identify and remember the bad practices I used so I don’t repeat them in the future. And I am sharing it with you, even though it is a bit humiliating to do so, in case it is helpful for anyone. If you followed any of my bad advice this summer and similarly screwed up your tomatoes, I hope that the hours of effort that I’ve put into these posts might also serve as a sufficient apology.

Let’s grow some better tomatoes in 2021!

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