The advantages of hydroponics are usually listed as a stack of superlatives without a single number. This page works differently: every claim gets a value — and at the end you get the list of what hydroponics does not solve.
Water: the 90% figure is not marketing
In a garden bed most of the irrigation water never reaches the root. Some drains below the root zone, some evaporates off the whole soil surface, some is drunk by weeds. In a closed system the water circulates: the only losses are what the plant actually takes up and releases through its leaves.
| Classic garden bed | Closed hydroponic system | |
|---|---|---|
| Water per kilogram of lettuce | around 250 L | around 20 L |
| Lost to drainage | 40–60% of what you pour | 0% |
| Surface evaporation | the entire bed | just the tank opening |
| Water that actually enters the plant | the minority | almost all of it |
The 250-versus-20 litres per kilogram comes from side-by-side trials in the same climate and applies to closed systems. Open systems that dump the solution down the drain do not get that benefit — put honestly: the saving comes from the closed loop, not from hydroponics as such.
In tower practice: 32 plants in full summer growth drink 3 to 6 litres a day. You top up a 40 L tank every 3 to 5 days, a 50 L tank roughly once a week. None of it drained away — that water literally went into the plants.
Footprint: 32 plants on half a square metre
A head of lettuce in a bed needs 25 to 30 cm of spacing, so 11 to 16 plants per square metre. For 32 heads you need 2 to 3 m² of bed. A vertical tower has a base diameter of about 50 cm — that is 0.2 m² of footprint, and realistically half a square metre once you allow room to walk around it.
- Tower 180 cm tall, 32 planting sites, footprint about 0.2 m².
- The same number in a bed: 2–3 m². A factor of 4 to 6.
- No bending — the top row sits at chest height, the bottom row at knee height.
- A 4 m² balcony takes two towers and still leaves room for a table.
Speed: why the lettuce is ready earlier
A root sitting in solution spends no energy searching. Nutrients are permanently available, inside the right pH window, with oxygen at the root. The result is a shorter cycle — not because the plant is different, but because the bottleneck is gone.
| Crop | In soil (from sowing) | In hydroponics | Difference |
|---|---|---|---|
| Rocket / arugula | 35–45 days | 21–28 days | about 35% |
| Head lettuce | 55–70 days | 30–40 days | about 40% |
| Spinach | 45–55 days | 30–40 days | about 25% |
| Basil, first cut | 50–60 days | 30–35 days | about 40% |
| Lamb's lettuce | 60–75 days | 40–50 days | about 30% |
An important caveat: those figures hold at 18–24 °C with enough light. In November on a north-facing balcony without LEDs nothing grows fast, whatever the system. Light is the limit, not the method — more in Lighting.
No weeds, no digging, no preventive spraying
- Weeds: no soil, no weed seed bank, no weeding. That is 1–2 hours a week that simply disappear during the season.
- Slugs: rarely climb a metre of smooth PETG. Rarely, not never.
- Soil-borne disease: wireworms, soil fungi and nematodes have nowhere to live.
- But: aphids, thrips and whitefly arrive by air. Hydroponics is not a sterile zone — see Pests and diseases.
- The real benefit: because you never spray preventively, control stays mechanical and biological — sticky traps, soft-soap solution, beneficial insects.
Year-round — and what that costs
Outdoors in Central Europe a tower runs roughly from April to November. Indoors under LEDs it runs twelve months, but then lighting is the biggest line on the bill — not the pump.
| Item | Amount | Note |
|---|---|---|
| Tower, one-off | 299.99–369 € | pump included |
| Pump electricity | 0.60–1.20 € per month | 5–10 W, depending on duty cycle |
| LED lighting (indoors) | 2.50–4 € per month | 40–60 W, 14 hours a day |
| Nutrients | 15–25 € per season | for all 32 sites |
| Substrate cubes | 0.10–0.20 € per plant | rockwool or foam |
| pH and EC meter | 35–70 € one-off | plus calibration solutions |
The maths without sugar-coating: at 5 cycles a year and a realistic 28 of 32 plants making it, that is about 140 heads. At a 1.20 € shop price that is 168 € of value per year. So the tower does not pay for itself in the first season — it pays in the second, and only if you actually keep it full.
Drawbacks you should know before buying
- Dependence on power. If the electricity fails in summer, the top rows notice after 4 to 8 hours. At night and in cool weather the problem is far smaller. Fix: a small UPS for 30–50 €.
- No buffer. Soil forgives mistakes for weeks, water forgives nothing. Overdose the fertiliser and the plant reacts within 24 hours. That is why measuring is not optional.
- Not every crop fits. Potatoes, carrots, beetroot, pumpkin and sweetcorn are out. Tomatoes and cucumbers work, but need support and far more nutrients than lettuce.
- The water warms up in summer. Above 24–26 °C dissolved oxygen drops and the risk of root rot rises. Keep the tank shaded, not on south-facing concrete.
- Algae. Any light hitting the solution grows a green film — see Algae.
- Getting started is not free. A bed starts with a packet of seed; a tower is a piece of equipment you buy.
Said plainly: if you have 200 m² of garden, good soil and well water, hydroponics solves nothing for you. It is the answer to missing space, scarce water and scarce time — and there it genuinely is the better option. What that looks like as an actual build is described in The vertical tower.