Tomato Science

I’m incredibly lucky to have some dedicated roof space. One of the primary activities I had planned for it is to grow some of my own food, particularly tomatoes. Tomatoes are very easy to grow, come in a lot of varieties, and home grown tomatoes are infinitely better than store bought tomatoes. Last year, I had a pretty successful harvest overall, but thought that some of the plants produced less than others, though it was hard to tell if the plants which produced a small number of large tomatoes were really outdone by the plants which produced a large number of small tomatoes. I was also curious to track more closely when the growing season started and ended. Putting all of that together, this year I decided to measure the harvest daily, to understand growing and total production patterns.


Growing Methodology

Starting from seed

Last year I bought a variety pack of tomato seeds from Amazon, so this year I used all of the leftovers from those endeavors. I didn’t take any care to store the seeds in any particular way, so they were probably a bit degraded from where they started off last year. Last year, I started them in tiny piles of dirt in egg cartons, but found that difficult to water consistently. This year, I started them in hydroponic root starter plugs, and 3d-printed a little holder to keep them in some spare Akro-Mils bins. Unfortunately I can’t find the CAD file or STL for the little 3d-printed stand, but if if you want it, drop me a note and I’ll make it again.

This method for getting the seeds started worked incredibly well, as I could easily tell how much water was sitting in the bin and top it off as necessary. After about a week or two, I had a good number of sprouts.

Early Growing

By about mid April, the sprouts had easily outgrown their seed starter tray, so I transferred them to 6” pots. I wanted to keep them mobile in case the weather got really cold or there was heavy rain predicted, either of which are possibilities for NYC in April.

The tomatoes lived in the 6” pots for a few weeks while everything warmed up, then I transferred them to a planter box permanently outside on May 8th.

In late May, I went on a vacation and then went to London for two weeks for work, so I made a diagram of all of the plants and got a friend to water them - they needed watering about every 2-3 days at this point.

For whatever reason, the hot peppers that I started from seed at the same time as the tomatoes took quite a bit longer to sprout, it wasn’t until late June that they were finally big enough to go in the planter box. I’ll try to remember to start them much earlier next year.


July 2nd was the first day we had a tomato ripe enough to harvest. It was a plum tomato and weighed 19g. My plan from here was to record the weight of produce produced by each plant every day that we harvested anything. From there, things started ramping up pretty quickly.

NYC had a particularly hot summer, and the tomatoes definitely suffered from it. I watered them daily for a while, relatively huge quantities of water, but what they really could have used was a bit of shade cloth. The roof also got much warmer than the ambient ground temperature, which was another reason I wanted to do my Home Assistant / weather station project.

Of course, we also made some things with all of those tomatoes - they were all delicious.


First, the data is all available for download if you’re curious (CSV format, values are grams of produce for each day). I stopped recording on Sept 9 because I got lazy, and also the amount of produce we harvested after this date was relatively small and low-quality.

The total tomato harvest was 5495g (12 lbs 1.8 oz), and the total pepper harvest was 610g (1 lbs 5.5 oz). The most productive plant was the plum tomato, at 1644g (3 lbs 10 oz), closely followed by the red cherry tomato, at 1450g (3 lbs 3.1 oz). Online resources suggest 8-10 lbs per plant isn’t at all unreasonable, so I’m clearly underperforming here. I would attribute the underperformance mostly to a relatively short and hot growing season, compared to a more temperate climate. I also didn’t really do much about fertilizer, just sprinkled some Osmocote something-or-other on about halfway through the season when I remembered, as well as some Cal-Mag, since I’d experienced some fruit rot last year.

In case any of those interactive links ever stop working, here’s also some rendered images of the graphs:

Next year, I’d like to get the weather station + soil temperature monitor working, and I’ll make sure to remember to start the peppers earlier.

Anyway, thanks for reading :)

Tags: #engineering