November 3, 2026

Watering tomato plants by how dry the bed reads

Water tomato plants when the soil around their roots begins to dry, then water deeply enough to wet the whole root zone. No fixed schedule fits, because heat, wind, rain, and your soil all change how fast a bed dries. A deep raised bed in a wet summer can go long stretches without the hose. A pot on a hot patio can dry out in one afternoon.

Why tomatoes need even moisture

A tomato carries calcium from the soil to its fruit in the water that flows up through the plant. Calcium rides that flow and barely moves once it's in place. When the soil dries during fruit set, the flow slows and the fast-growing tip of each young fruit runs short. Those cells collapse into the dark, leathery patch called blossom end rot.

Splitting comes from the opposite swing. After a dry spell, a heavy soak pushes water into ripening fruit faster than the skin can stretch, so the skin cracks. Soggy soil causes its own trouble, because water fills the pore space and roots run short of oxygen. A bed that stays evenly moist avoids most of all three.

What our tomato bed read through fruit set

We transplanted tomato seedlings into raised bed 2 in our own garden on May 18. From July 13 to September 10, its soil moisture probe read between 36% and 57%. That window took in our hottest day of the year, 97°F on August 5.

Rain did much of the work. July brought 10.89 in and August brought 6.56 in. September had brought only 1.35 in, and the bed hit its low of 36% on September 6 as the rain fell off. We picked 30 tomatoes, 1.7 lb in all, between August 17 and September 7.

In those weeks, the shallower ground bed ranged between 32% and 62%. It holds 8 in of soil against 24 in for the raised beds. Less soil holds less water in reserve, so it dries and refills faster. A shallow bed needs checking more often than a deep one.

When rain lets you skip watering

Rain that soaks the root zone counts as a watering. The watering guidance on the Today screen is free and works for the whole garden. A forecast of 5 mm or more across today and tomorrow turns the watering guidance on the Today screen to hold. Rain of 5 mm or more in the last three days turns the watering guidance to covered. With neither, it says water.

Those signals cover the garden as a whole. A bed under eaves or a dense tomato canopy can catch less of a light shower than open ground. Treat covered as a cue to check that bed before you reach for the hose.

How to check the bed before you water

Push a finger or a trowel into the soil near the base of the plant, below the dry surface crust. Dry soil crumbles and feels warm. Moist soil holds together and feels cool, because water evaporating from it draws off heat. Our guide to setting up a raised tomato bed with a sensor covers where a probe goes.

On Pro, a soil probe mapped to a bed sends a dry alert when the two most recent readings are both below 25%, or both above 60 cb on a Watermark probe. Requiring two readings keeps one stray reading from setting it off. You get at most one dry alert per bed per day. Siltwell tells you which bed is dry and leaves the watering to you.

Suppose your tomato bed reads 28% on a hot afternoon with no rain in the forecast. No alert has fired yet, but the bed is heading toward dry. A deep soak the next morning keeps it from swinging low while fruit is setting.

A probe reads the soil around its tines and nothing else. Set it beside a drip emitter and it reports the wettest spot while the far end of the row dries. The 25% line is also a fixed number that knows nothing about your soil type. In our raised beds the readings stayed above it from July to September.

Watering in hot weather

Heat speeds up how fast leaves lose water. A tomato can wilt at midday in moist soil because its roots can't keep pace with its leaves. If the soil is moist and the plant recovers by evening, hold off. If the soil is dry and the leaves stay limp into the evening, water deeply that day.

Water early in the morning so the leaves dry in the sun, which gives leaf diseases less wet time to take hold. Our guide to the best time to water your garden goes through the timing. Soil with plenty of organic matter also holds moisture more evenly, as our guide to the best soil for tomatoes explains.

If you run drip line, check the soil at root depth before a run and again an hour after. Lengthen the run until the reading rises across the root zone, then let the bed dry back toward its low end before the next one. Our guide on drip tubing run frequency shows how to set run length from the soil.