35 studies, every one cited on the page where it is used. A tomato plant is run by soil, water, light and temperature. Every process inside it — germinating, growing, setting fruit, colouring, building flavour — has its own window on each of those four, and the windows do not line up. Stack the five in-season temperature windows and the band where all of them are at their best at once is about four degrees wide. Outside it the plant does not die. It quietly switches off one function at a time, and each one leaves a mark you can learn to read. That is why a tomato can look magnificent and set nothing, or swell fruit that never turns fully red. This is a field manual to those four dials, with the study behind every number. What is in it - The nine-day rule — high temperature damages pollen about nine days before the flower opens, so the heatwave that cost you the truss is last week's, and by the time you see bare flowers the weather has changed and nothing looks wrong. - Why blossom-end rot is not a calcium deficiency. Calcium deficiency is a *result* of it, adding calcium to soil does not reliably fix it, and the blossom end of each fruit is served by only two thin xylem strands for its first two weeks. It is a water management problem. - The temperature at which red stops. Above about 30 °C on the fruit surface lycopene synthesis is inhibited and the plant makes orange carotenoids instead — which is the real argument against stripping leaves off your trusses. - Daily light integral explained from scratch, with the odd fact that tomato is one of the few crops injured by too much light: past about eighteen hours a day the leaves go chlorotic and the yield stops rising. - Crop coefficients and vapour pressure deficit — how many litres, when, and a computed VPD table you can read your own greenhouse off. - The measured exchange rate between yield and flavour under deficit irrigation, from a meta-analysis of 25 studies, so you can decide rather than be sold a slogan. - Cracking, and why hard thinning and generous watering — two things people do out of care — make it worse. - Soil pH, EC and containers, including why half of all "deficiencies" are a pH problem in disguise. And the part that makes it usable A lag table giving, for every symptom, how many days back the cause was. A fault finder arranged by what you can see rather than by disease name. Five faults that are always misdiagnosed. Three printable worksheets — your site, your season log, a fault trace. And every number in the book on one printable page. What it is not Not a pest and disease manual and not a variety guide. Not medical or dietary advice. Where a figure comes from field trials on commercial crops, the book says so, because a number measured on hectares needs translating before you apply it to six plants in pots. Where no measured figure exists, it says that too, instead of filling the gap with something plausible. Formats: PDF (US Letter, laid out page by page) and reflowable EPUB for Kindle, Kobo, Apple Books and phones. Both included. Instant download, nothing ships. Plain English throughout. Metric first, imperial in brackets. International by default.