How Far Apart Should You Plant Tomatoes?

The question comes round every spring, usually with a tray of young plants in hand: how far apart should tomatoes go? You want one number, something you can measure off a string line. The answers you find vary by a factor of two, and for good reason: each one answers a specific situation without saying which.

Tomato spacing is not a constant. It is the outcome of a calculation with three inputs, and until those are settled, no number means anything.

Why there is no single number

Spacing plants means deciding how much room each one will occupy at full size. But a tomato plant has no fixed size. It depends on what the plant is genetically capable of doing, and on what you allow it to do. Two gardeners planting the same variety on the same day can end up, by August, with one narrow two-metre (6 ft) column and one sprawling bush covering a square metre of ground.

So a single number cannot be right. What can be given is a set of working distances for the common cases, along with the reasoning that lets you move them up or down.

Variety habit: cordon or bush

The first variable is printed on the seed packet, sometimes in small type. Indeterminate varieties (cordon or vine types) grow continuously for as long as the season allows: the main stem keeps extending, and it needs support and training. Most classic garden tomatoes work this way. Determinate varieties (bush types) stop growing at a set height and form a compact plant that sets and ripens its fruit over a shorter window.

The two habits occupy space differently. A trained cordon occupies mostly vertical space; its footprint stays modest, so it can sit closer to its neighbour in the row. A bush type spreads sideways, often without support, and needs a more generous footprint even though it stays low. This is counter-intuitive: the taller plant is not the one that needs the most ground.

Dwarf and patio varieties are a third case with their own figures, usually given by the grower on the plant label.

Training: how many stems, and what you do with side shoots

The second variable is entirely yours. On an indeterminate tomato, every leaf axil produces a side shoot, or sucker, which if left in place becomes a full stem with its own foliage and its own trusses.

Growing a plant on a single stem, pinching out every sucker, gives a narrow, legible plant that can sit closer to the next. Running it on two stems roughly doubles its leaf volume, and in practice you should allow something approaching the space of two plants. Not pinching at all, which is a perfectly defensible choice, produces a wide bush that has to be spaced accordingly.

The classic mistake is to adopt a spacing you read somewhere for single-stem training, then decide in June to let the suckers run because there is no time to pinch. The spacing becomes wrong retroactively, and the row closes over.

What spacing actually protects: airflow and drying time

Spacing is often explained in terms of root competition for water and nutrients. That competition is real, but it is not the deciding factor, and it can be partly offset by watering and feeding.

The real issue is above ground. Late blight, the main threat to outdoor tomatoes in temperate climates, needs persistent moisture on the foliage to establish. Anything that shortens the time leaves stay wet reduces the risk; anything that lengthens it raises the risk.

That is precisely what spacing governs. Crowded plants form a mass of foliage that air moves through poorly. After rain, dew, or a careless watering, that mass dries slowly: the leaves stay wet through part of the morning instead of drying within the hour. The question is not only whether the plants have enough soil, but whether air can move between them and carry the moisture away.

This also gives you the rule for adjusting. An open, breezy, outdoor site allows tighter spacing. A sheltered corner behind a hedge or wall, and above all a greenhouse or polytunnel, where air stagnates and humidity climbs overnight, calls for the opposite: open the spacing up.

Working distances, and how to adjust them

Here are the figures most commonly used. They are starting points rather than measured values, and they assume open ground with reasonable sun.

For an indeterminate variety, supported and grown on a single stem, 45 to 60 cm (18 to 24 in) between plants along the row is the usual range. On two stems, it is wise to move to 60 to 80 cm (24 to 32 in). For a determinate bush variety left untrained, allow 60 to 80 cm (24 to 32 in) as well, and more for the most vigorous ones. An indeterminate left unpinched as a bush needs at least as much.

These ranges shift. Under glass or plastic, take the top of the range as a matter of course, or a step beyond it: that is the setting where blight and mildew are least forgiving. On a windy site with soil that drains and dries quickly, the bottom of the range is fine. A variety known to be vigorous, with heavy foliage, should be treated as one step above its nominal habit.

Between the rows, and in a small garden

Row spacing is the part most often neglected. Gardeners get the in-row spacing right, then set the rows 50 cm (20 in) apart and cancel the benefit: two close rows together form a wall of foliage, with exactly the same effect on airflow as a row planted too tight.

Somewhere between 80 cm and 1 m (32 to 40 in) between rows is a reasonable outdoor benchmark, and more under cover. That is not wasted ground. It is the access that lets you harvest without brushing the foliage, water at the base without wetting the leaves, and inspect the underside of the plants, which is where the first blight lesions show.

Then there is the small-garden temptation. When space is tight, you squeeze the row to fit one more plant in. The reasoning sounds solid and rarely is. The extra plants shade one another, photosynthesis drops in the lower layers, foliage stays wet longer, and the first outbreak of blight spreads from plant to plant with nothing in its way. The mechanism is easy to follow: every plant you add takes light, air, and water from its neighbours, and raises the disease risk for the whole group.

In a small space, the better trade is a different one: fewer plants, grown on a single stem, properly supported, with real access between them. Three healthy plants crop for longer than five crowded ones that defoliate together in the first humid week of August.

Where Marmanda fits in

Marmanda lays your crops out on the space you actually have, holding to the spacing each variety and training method requires, rather than leaving you to judge it by eye. The data it uses is shown with its source and its limits, including where a figure is a common working range rather than a measured value.

The useful question, in the end, is not "how far apart?" but "which plant, trained how, and grown where?". Answer that one, and the distance follows.