A vertical tower is a hydroponic system in which plants sit stacked around a central pipe. Technically it is drip irrigation with a return line — an idea decades old. Going vertical changes two things: how many plants fit on a square metre, and how light is distributed among them. Both come at a cost worth knowing before you buy.
How the tower works, step by step
- Reservoir (40 or 50 L) sits at the bottom and carries the whole structure. It holds the nutrient solution and the submerged pump.
- Pump pushes water through a riser pipe in the centre of the tower right to the top — in our case a Sicce Syncra Silent 2.0, 230 V, 32 W.
- Sprinkler at the top spreads the water over the inner wall of the top module instead of dumping it in one spot.
- Modules (6 plus a top module, 32 slots in total) hand the water down from level to level. The solution drips over the roots and falls to the next storey.
- Return — the bottom module lets the solution run back into the tank. The loop is closed and nothing leaches into the surroundings.
The roots never stand submerged. They hang in the moist, airy space inside each module and receive water in pulses. That is why root oxygenation is excellent without a single air stone — the air is already there.
Pump, head height and interval
Here is the number most product pages leave out: a pump never delivers its rated flow when it has to lift water. The Sicce Syncra 2.0 is specified at 2150 l/h, but that applies at zero metres of head. At 1.8 m — the height of the tower — real flow drops to roughly a fifth to a third of that. This is why the pump has to look oversized: it is the only way enough water reaches the top. A 500 l/h pump moves practically nothing in a 180 cm tower.
| Mode | Hours per day | Power per month | When it makes sense |
|---|---|---|---|
| 15 min on / 45 min off | 6 h | ~5.8 kWh | Winter, cool days, mature plants |
| 15 min on / 15 min off | 12 h | ~11.5 kWh | Spring and autumn |
| Continuous | 24 h | ~23 kWh | Summer heat, young transplants |
For scale: 23 kWh a month at 0.25 €/kWh is about 6 € — so even the most expensive mode costs less than two coffees a week. Set the interval with an ordinary plug-in timer; the tower needs no smart electronics and no app.
Vertical versus flat — an honest comparison
| Criterion | Vertical tower | Flat system (DWC or NFT table) |
|---|---|---|
| Plants per m² of floor space | up to 64 (32 on 0.5 m²) | 16–25 |
| Light distribution | Uneven, the top gets most | Even across every slot |
| Buffer during a power cut | 4–8 h in summer, roots dry out | Days, roots sit in water |
| Cleaning | Dismantle 7 modules, 1–2× per season | One basin, quickly done |
| Fruiting crops (tomato, pepper) | Top modules only, with support | No restriction |
| Harvesting | At arm height, no bending | Bending or a work bench |
The tower's real weakness is its dependence on the pump. In a DWC system the roots hang in water and survive a multi-day failure. In a tower they depend on the drip: at 30 °C the first plants start wilting after roughly four to six hours without water. If power cuts are common where you live, plan for it or add a small UPS.
Where to put the tower
- Light: at least 4–6 hours of direct sun for leafy greens, 6 or more for strawberries and fruiting crops. Indoors, LED lighting must stand beside the tower, not above it — from above only the top module gets lit.
- Wind: a full 40 L tank weighs about 40 kg and keeps the tower stable. Empty, it topples in a strong gust — never leave it empty on an open terrace. Against a wall or railing is safest.
- Power: a socket within cable reach. Outdoors an IP44 socket and an RCD are mandatory. Route the cable in a drip loop below the socket so water drips off the loop rather than running into the contacts.
- Heat: above 24 °C the solution loses oxygen and root rot gets its chance. At 20 °C water holds around 9.1 mg/L of oxygen, at 30 °C only about 7.6 mg/L. A white wall reflecting midday sun can raise tank temperature by 5 °C — ideally sun for the leaves, part shade for the tank.
- Space: the footprint is 0.5 m², but allow a circle roughly 1 m across so you can walk around and harvest.
- Winter: below freezing the tank, pipe and pump must be empty. Ice forces joints apart and destroys the pump rotor.
What grows on which level
Light comes from above, so the upper modules get the most sun hours and dry out fastest, while the lower ones work in part shade. That is not a flaw if you plan your planting around it.
| Position | Conditions | Suitable plants |
|---|---|---|
| Top module (level 1–2) | Most sun, dries faster | Basil, strawberries, cherry tomato with support |
| Middle (level 3–4) | Balanced light and moisture | Lettuces, pak choi, chard, rocket |
| Lower modules (level 5–6) | Part shade, cooler, damper | Spinach, lamb's lettuce, parsley, mint |
Root vegetables (carrot, beetroot, potato) do not belong in a tower — a 5 cm net pot leaves no room to swell. Tall fruiting crops technically work but shade everything beneath them, so keep them on the north side of the tower or limit yourself to two plants per tower. Routine care is covered in Tower maintenance.