Q: What is the best temperature for growing tomatoes?

Between 21 and 25 °C. That is the narrow band where five separate processes — vegetative growth, root-zone uptake, pollen development, fruit set by day and lycopene synthesis — are all simultaneously at their published optimum. Outside it the plant does not die; it switches off one function at a time, and each one leaves a different visible mark.

Q: Is blossom end rot a calcium deficiency?

No. Calcium deficiency in the fruit is a result of the disorder rather than its cause, and raising soil calcium does not reliably raise fruit calcium or reduce the rot. The blossom end of each fruit is served by only two thin xylem strands for its first two weeks after set, and delivery depends on steady transpiration. It is a water-management problem.

Q: Why will my tomatoes not turn fully red?

The fruit is too warm. Above roughly 30 °C at the fruit surface, lycopene synthesis is inhibited and the plant builds orange carotenoids instead; by about 35 °C it has stopped. That is the argument against stripping leaves off a truss to expose the fruit to sun — the leaves were providing the shade.

Q: What format is The Science of Growing Tomatoes supplied in?

Two files, both included in one price and delivered as an instant download: a 54-page PDF laid out page by page for US Letter, and a reflowable EPUB for Kindle, Kobo, Apple Books and phones. Nothing ships and there is no subscription.

Q: Does this guide work outside the United States?

Yes. It is built on temperatures, daily light integrals, crop coefficients and pH rather than on planting dates, so nothing in it depends on a hardiness zone or a hemisphere. Metric units are given first with imperial in brackets throughout.

Why do tomato flowers drop without setting fruit?

Usually heat about nine days earlier. Pollen is built before the flower opens, and high temperature damages it during that build — sustained days around 31 to 32 °C, or nights over 24 °C. By the time bare trusses are visible the weather has changed, so the useful move is to look back nine to fourteen days rather than at today.

Move the slider

What is the best temperature for growing tomatoes?

Between 21 and 25 °C — but only because that is the narrow band where five separate processes are all at their published optimum at the same time. Outside it the plant does not die. It switches off one function at a time, and each one leaves a different mark. Drag the slider and watch which ones go.

23°C

Air temperature in degrees Celsius

Five published temperature windows, drawn from the figure on page 13 of the book. The pale bar is the range in which the process runs at all; the red bar is its optimum. Sources for each row are cited on the page itself.

The lag

Why is my tomato problem not caused by this week’s weather?

Because you never see a cause. You see a symptom, and by then the weather that caused it has changed. High temperature damages pollen about nine days before the flower opens, so the heatwave that cost you the truss is last week’s and nothing looks wrong today. Every symptom has its own lag.

Pick a symptom. The answer is one row of the book’s lag table — five of the eleven rows are shown here.

What you can see

9–14 days

Look back

At which dial: Day and night temperature

From The lag table, chapter thirty-one. The full table carries eleven symptoms, each with its sources.

Straight answers

Three things this book says that your usual advice does not

Is blossom end rot a calcium deficiency?

No. Calcium deficiency in the fruit is a result of the disorder rather than its cause, and raising soil calcium does not reliably raise fruit calcium or reduce the rot. The blossom end of each fruit is served by only two thin xylem strands for its first two weeks, and delivery depends on steady transpiration. It is a water-management problem.

What to do instead: make the water supply monotonous — the same amount, at the same time, without the dry-then-flood cycle that most people water on. The book gives the method, the VPD band to aim at, and the root-zone temperature that has to be right for any of it to work.

In the book: chapter seventeen, and fault 1 of five that are always misdiagnosed. Every claim carries a numbered source.

Why do my tomato flowers drop without setting fruit?

Almost always heat, about nine days ago. Pollen is built before the flower opens, and high temperature damages it during that build. Sustained days around 31–32 °C, or nights over 24, and the flower opens with pollen that cannot do the job. By the time you see bare trusses the forecast looks fine and you are treating the wrong week.

What to do instead: look back nine to fourteen days at both day and night temperature, and protect the flowers that have not opened yet. Fruit set is the narrowest window the plant has, which is why the book ranks it first in its decision procedure.

In the book: the nine-day rule, chapter four — and the lag table, which gives the look-back for ten other symptoms.

Why won’t my tomatoes turn fully red?

The fruit is too warm. Above roughly 30 °C at the fruit surface, lycopene synthesis is inhibited and the plant builds orange carotenoids instead; by about 35 °C it has stopped. That is the real argument against stripping leaves off a truss to “let the sun at it” — the leaves were the shade.

What to do instead: shade the fruit, not the plant, and treat colour as reversible — every hour under 30 °C is an hour of lycopene. The book ranks colour second in what to protect when the weather is outside the corridor, because partial protection genuinely helps.

In the book: chapter six, with the measured inhibition thresholds and what they mean for leaf cover.

Look inside

Four real pages, not a mock-up

Every figure in this book was drawn for it from the numbers in the source cited beside it. There is no stock photography and no illustration that is not made of data. Tap any page to read it full size.

What is in it

Six parts, 54 pages, and a back section you will actually use

Part one

Temperature

Germination, growth, truss formation, the nine-day rule, colour and the root zone — then all five windows stacked into one corridor and one decision procedure.

Part two

Light

Daily light integral from scratch, how much your own site gets, and the eighteen-hour ceiling past which the leaves go chlorotic and yield stops rising.

Part three

Water

Crop coefficients, a computed VPD table, blossom-end rot, cracking, and the measured exchange rate between yield and flavour under deficit irrigation from a meta-analysis of 25 studies.

Part four

Soil

pH 6.0 to 6.8 and what happens outside it, EC, structure and air, why containers are a different planet, and a soil test you can act on.

Part five

The season

Six stages in one table, stage by stage, the same plant in three climates, and what to do when you cannot change the weather.

Part six

Reading it backwards

The lag table. The fault finder arranged by what you can see. Five faults that are always misdiagnosed. Three printable worksheets. Every number on one page.

Before you buy

What this book is, and what it is not

It is

A field manual to four measurable inputs, with the study behind every number.
Plain English. Metric first, imperial in brackets. International by default.
Honest about its limits: where a figure comes from field trials on commercial crops, it says so, because a number measured on hectares needs translating before you apply it to six plants in pots.
Explicit where no measured figure exists, instead of filling the gap with something plausible.

It is not

A pest and disease manual.
A variety guide.
Medical or dietary advice.
A book of rules of thumb. If you want “water deeply, twice a week” with nothing behind it, this is the wrong guide — it will tell you the crop coefficient and let you do the arithmetic for your own site.

About the author

Abdelmounim El Moussaddar

An engineer, and an avid reader and researcher. These guides come out of a habit rather than a profession: reading the primary literature on something ordinary, finding that the widely repeated advice and the measured evidence disagree, and wanting the disagreement written down somewhere useful.

Every number in The Science of Growing Tomatoes was taken from a named source and carries a superscript to the reference list. Nothing was rounded into confidence. Where the evidence is thin the book says so. If you find an error, it is an error, not a simplification — corrections are welcome and get made.

Questions

Reasonable things to ask before spending money

What exactly do I get, and how?

Two files, immediately, as a download: a 54-page PDF laid out page by page for US Letter, and a reflowable EPUB for Kindle, Kobo, Apple Books and phones. Both are included in the one price. Nothing ships and there is no subscription.

Will this work where I live?

Yes. The book is built on temperatures, light totals, crop coefficients and pH rather than on planting dates, so nothing in it depends on a hardiness zone or a hemisphere. Metric is given first with imperial in brackets throughout. The one thing you supply is your own site, and there is a worksheet for measuring it once.

Is it for greenhouse growers or outdoor growers?

Both. The four dials are the same either way; what changes is how much control you have over each. Part five walks the same plant through three climates — a cool maritime summer, a hot continental one and a glasshouse — and the chapter on what to do when you cannot change the weather is written for people growing outdoors in pots.

I have grown tomatoes for years. Is there anything new here?

The book is aimed squarely at the gap between what is commonly repeated and what has actually been measured. Five faults get a chapter of their own because the standard explanation for each is wrong and the standard treatment therefore does not work — blossom-end rot as a calcium problem, purple spring leaves as a phosphorus shortage, blossom drop as today’s weather, splitting as yesterday’s watering, and a magnificent plant with no fruit as underfed.

Where do the numbers come from?

Thirty-five numbered sources — peer-reviewed horticulture journals, university extension publications and standard reference works — every one of them cited inline at the point it is used, not gathered in a bibliography nobody checks. Where two studies disagree, the book reports both rather than picking the tidier one.

Can I print it?

Yes, and three pages are designed for it: your site measured once, the season log, and the fault trace. So is the summary page that carries every number in the book. The PDF is laid out for US Letter at full bleed with no cropping required.

Tomato Growing Guide - 54-Page PDF + EPUB, 35 Cited Sources - Soil, Water, Light and Temperature - Blossom End Rot, Fruit Set and pH