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Build manual · Deep water culture · Fruiting crops

DWC Cherry Tomato: one plant, 25 L, 600 PPFD, and a daily top-up habit

A single indeterminate cherry tomato in deep water culture is the highest-yield plant per square metre you can grow indoors, and the least forgiving. It will drink four litres a day at peak, and every failure mode is a consequence of missing a check.

By The Grow DeskPublished 19 Oct 2026Difficulty Intermediate
System specification110 day cycle
Reservoir
25 Lworking volume
Planting sites
1sites
Pump
120 GPH454 L/h
Air stones
2stones
EC target
2 mS/cmtarget
pH window
5.8 - 6.2pH
Light at canopy
600 PPFDat leaf
Photoperiod
16 hper day
Cycle length
110 daysplant to harvest

Top-up routine — A single cherry tomato in a 25 L DWC can drink 3-4 L per day at peak; check daily and top to the mark with 2.0 mS/cm nutrient.

Bill of materials8 line items
Bill of materials
PartSpecificationQtySubstitute
Reservoir25 L opaque bucket with lid, 35 cm diameter1A 20 L bucket works but the daily draw at peak leaves almost no margin
Net pot100 mm rim, deep basket1A 75 mm pot is enough if you plant a determinate variety rather than a sprawling one
Air pumpDual outlet, 3 W, 2 x 1.5 L/min1A single 60 L/h pump with one large bar stone is acceptable but less even
Air stones5 cm round, fine pore, opposite corners2A 15 cm bar stone laid across the bottom covers a 35 cm diameter well
Growing mediumLECA 8-16 mm, 3 L3 LRockwool cube in a LECA collar holds the stem steadier for a tall plant
Cherry tomato seedling5 weeks, indeterminate, first truss visible1A determinate bush type keeps the plant under 1 m in a tent
Fruiting nutrientTwo-part high K, 2.0 mS/cm1 L eachDry salts: 1.8 g/L calcium nitrate plus 0.9 g/L potassium sulfate at peak
Trellis1.8 m stake plus 3 m of soft twine1A yo-yo hanger clipped to the tent frame lets you lower the plant as it grows
Assembly, in order6 steps

  1. Set the water 2 cm below the pot base, not touching

    A single large plant in a 25 L bucket has a big root mass and does not need the pot sitting in water after the first week. Run the initial level 2 cm below the net pot, let the airstones throw moisture into the gap, and the roots will reach down on their own within four days with far less risk of stem rot.

  2. Two stones at opposite corners, always

    One stone under a tomato plant that is drinking 4 L a day creates a single oxygenated column and a large dead zone on the far side. Two stones at opposite corners of a 35 cm bucket keep the whole volume turning over, which matters more here than in a shallow tote because the water column is deeper.

  3. Start at 1.4 and reach 2.0 by the third truss

    A cherry tomato in DWC grows explosively and it is tempting to feed it hard from the start. Resist it. 1.4 mS/cm until the first truss sets, 1.7 at the second, 2.0 from the third onwards. A plant pushed early produces a huge vine with sparse, poorly filled trusses.

  4. Remove every side shoot below the third truss

    An indeterminate cherry tomato in a tent will produce a side shoot at every leaf axil. Removing them all below the third truss and then weekly above it keeps the plant as a single productive vine and dramatically improves airflow, which is the main defence against botrytis in a still tent.

  5. Shake the trusses to set fruit

    Indoor tomatoes have no wind. A gentle flick of each open truss with a finger at midday releases the pollen and is the difference between a full truss of evenly sized cherries and one with half the flowers dried and dropped. Do it every day while a truss is in flower, for about a week.

  6. Change the reservoir every two weeks at peak

    On a single plant drinking 4 L a day, the 25 L reservoir turns over completely in under a week. Root exudates accumulate fast at this rate, so a full dump-and-recharge every two weeks during fruiting keeps the root zone clean. Waiting for a visible problem means waiting until the roots are already brown.

Week-by-week maintenanceWeek 1-3 · Week 4-7 · Week 8-13 · Week 14-16

Week 1-3

EC 1.4 · pH 6.0

  • Level 2 cm below the pot
  • Remove side shoots below the first truss
  • Shake trusses at midday

Week 4-7

EC 1.7 · pH 6.0

  • Reach 1.7 at the second truss
  • Keep only one vine
  • Top up every 2 days

Week 8-13

EC 2.0 · pH 6.1

  • Full EC during fruiting
  • Daily top-up
  • Reservoir change every 2 weeks

Week 14-16

EC 1.8 · pH 6.1

  • Stop the vine two trusses above the last set fruit
  • Continue harvesting
  • Final flush in the last week

The reservoir turns over in under a week

Nobody warns you how fast a fruiting cherry tomato empties a bucket. University of Arizona CEAC puts mature greenhouse plants at roughly 4 liters per plant per day, and a DWC reservoir catches that full load — you end up topping up most days, not once a week. Top up with plain water and the EC slides south while the plant is still asking for full strength. For scale: commercial greenhouses fertigate at 2.5-3.5 mS/cm with the drain running about a unit higher, hold the root zone near pH 6.0, and feed N 200, P 50, K 360, Mg 45, Ca 185 mg/L (all University of Arizona CEAC). You can't copy those figures straight into a bucket, but the message carries over — a half-diluted reservoir is not feeding a plant that is setting fruit. Change the solution on a schedule instead of waiting for it to look wrong.

One vine, not a bush

Indeterminate cherry tomatoes do not politely stay small. Give one free rein in a tent and it becomes a multi-stemmed thicket that shades its own lower trusses, and the fruit that does set comes in small. I have grown it both ways: the unpruned plant looks magnificent in week five and slightly embarrassing by week nine. Keep one leader, snap side shoots out weekly while they are still soft, and you get something you can actually manage — trusses stacked up a stake, each one sitting in light. Light is the part people underestimate: fruiting hydroponic crops like tomatoes want 8-10 hours of sun a day (SARE), and they do best at 21-27 C by day with 16-21 C at night (University of Illinois Extension). An open canopy also moves air, which is most of the reason botrytis stays away.

Pollination is a job, not an afterthought

Tomato flowers are self-fertile, but the pollen sits locked in a cone that only lets go when something shakes it. Outdoors the wind and the bees do that for free. In a still tent, nothing does — a whole truss of open flowers can simply drop without setting. The fix is almost funny: at midday, when the air is driest, flick each open truss with a fingertip or tap the stake with a pen. An electric toothbrush pressed against the truss works too; the buzz is what matters, not the brand. In our tent the tapped trusses set visibly more fruit than the ones we left alone — nowhere near every flower, but the gap shows up on the scale at harvest. Skip it and you get rows of yellowed, empty trusses.

The airstones carry the whole system

In a deep column the bubbles are the only route oxygen has to the bottom of the bucket. A scaled-up stone still looks fine from above: bubbles rise, the surface ripples, nothing seems wrong. What you cannot see is dissolved oxygen falling away down at the root mass, and the lower roots are the ones feeding the fruit, so they are the first to stall. That is why I run two stones rather than one — not for extra volume, just insurance — and why I pull them for a scrub as soon as the bubbles feel coarse or the stone goes slick. A plant pulling close to 4 liters a day (University of Arizona CEAC) is also pulling a lot of oxygen. Air deserves the same attention you give nutrients.

Tubing diagram: DWC Cherry Tomato: one plant, 25 L, 600 PPFD, and a daily top-up habit
Tubing diagram: DWC Cherry Tomato: one plant, 25 L, 600 PPFD, and a daily top-up habit

Key points

  • One plant drinks 3-4 L a day at peak; check and top up daily
  • Keep a single vine and remove side shoots weekly
  • Start at 1.4 mS/cm, reach 2.0 by the third truss
  • Flick each flowering truss at midday to set fruit
  • Full reservoir change every two weeks during fruiting

Sources

Please noteEC, pH and light values are general home-system references and vary with variety, climate and nutrient brand. Follow the product label. This article is informational and is not professional horticultural advice.

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