Hydroponic Watering Schedule: Pump Cycles by System and Stage
In soil you water when the pot dries out. In hydroponics the plant sits on a pump timer, and the right setting depends on the system far more than on the plant. DWC and NFT have no watering schedule at all because the roots never leave the solution or the flow. Ebb and flow and drip do, and there the number of cycles per day changes with the medium and the stage. Below are the starting points by system, how to tune them by looking at the medium, and the second schedule every hydro grower keeps: solution changes.
Schedule by system: the starting points
Treat these numbers as a first timer setting, then adjust by the medium (next sections). Cycles are counted over the lights-on period: plants drink while the lights are on, and a flood or drip shot at night mostly keeps the medium wet for no reason. The last column is the rough time roots survive if the pump or air stops. It tells you how much a dead timer or a power cut costs in each system.
| System | Seedling / veg | Flower | Cycle length | Roots tolerate a stop |
|---|---|---|---|---|
| Ebb and flow, clay pebbles | 3-4 floods | 4-6 floods | 10-15 min, no floods at night | about 8 h |
| Ebb and flow, rockwool | 1-2 floods | 2-3 floods | 10-15 min, no floods at night | about 8 h |
| Drip, recirculating | 4-6 shots | 6-10 shots | 10-15 min | about 6 h |
| Drip to waste (coco, rockwool) | 1-2 seedling, 2-4 veg | 3-6 shots | short shots, 10-20% runoff per day | about 12 h |
| NFT | pump runs non-stop | pump runs non-stop | 1-2 L/min per channel | about 30 min |
| DWC / RDWC | no watering; air 24/7 | no watering; air 24/7 | air pump from 1 L/min per 4 L of solution | about 2 h |
| Aeroponics, low pressure | misting cycles | misting cycles | 30-60 s every 4-5 min | about 15 min |
| Aeroponics, high pressure | misting cycles | misting cycles | 2-5 s every 3-5 min | about 15 min |
| Kratky, wick | no pumps | no pumps | keep an air gap above the solution | n/a |
Ebb and flow: tune the timer by the medium
Oregon State University Extension gives a practical rule: flood to about an inch (2-3 cm) below the top of the medium, drain once the medium is fully soaked and glistening, and flood again before it dries out and starts pulling away from the pot. If the medium shrinks from the walls or plants wilt between floods, the next flood is late. Clay pebbles drain fast and hold little water, so they need more floods; rockwool holds a lot, so 1-2 floods in veg are often enough, and flooding it 5 times a day keeps the roots short of air. Bigger plants in flower drink more, which is why the count goes up in the second half of the grow. Change one thing at a time: add or remove one flood a day, watch for two or three days, and write down what you changed.
Drip: to waste and recirculating are different schedules
In drip to waste (usually coco or rockwool) each shot is short and the goal is a small daily runoff, around 10-20% of what you put in, so salts do not pile up in the slab. Start the first shot about an hour after lights on and stop 2-3 hours before lights off, so the medium dries back a little overnight. Seedlings get 1-2 shots a day, veg 2-4, flower 3-6. Recirculating drip sends the runoff back to the reservoir, so you can run longer and more frequent cycles: 4-6 in veg and 6-10 in flower, 10-15 minutes each. In both cases the rule is the same: the medium should never dry out completely between shots.
NFT, DWC and aeroponics: the schedule is "never stop"
In NFT the roots live in a thin film of solution running down the channel. The pump runs around the clock at 1-2 L/min per channel, with a slope of roughly 1:30 to 1:40; Oregon State Extension names 2% as the minimum grade. Putting an NFT pump on an interval timer is the classic mistake: a stop longer than about 30 minutes dries the roots. DWC has no pump for the solution at all; what matters is the air pump running 24/7 (from about 1 L/min per 4 L of solution) and, once roots grow, a 2-5 cm air gap between the lid and the water. In RDWC the circulation pump also runs non-stop. Aeroponics is the least forgiving: the misting timer runs in seconds and minutes, and a blocked nozzle or a dead pump dries roots within about 15 minutes.
The second schedule: solution changes and top-offs
Pump cycles decide how roots get water; solution changes decide what that water contains. A common starting interval is a full change every 7 days for DWC, NFT, ebb and flow, drip and aeroponics, about 10 days for a large RDWC system, and around 14 days for passive Kratky and wick setups. Between changes the plant drinks and the reservoir goes down, so you top off. Two signs mean the change is due early: you have already topped off as much solution as the reservoir holds, or EC has moved far from the value you mixed. In both cases the nutrient ratio in the tank no longer matches the recipe. If EC rises as the level drops, the plant is taking more water than nutrients: top off with plain water. If EC falls, top off with a weak solution.
How GrowScope helps
In GrowScope's hydroponics mode you describe the system once (method, medium, reservoir volume, pump timer or misting cycle, air pump). The Tent tab then shows pump and aeration guidance for the current stage with the same ranges as the table above and flags a setting that falls outside them, for example an NFT pump on a timer or too few floods for clay pebbles in flower. The reservoir log reminds you when the solution is due for a change and moves the date earlier if you have topped off a full tank or EC has drifted.
Key takeaway
Ebb and flow and drip run on cycles per lights-on day (more in flower, fewer in rockwool), while NFT, DWC and aeroponics must never stop. Tune the timer by how the medium looks between cycles, and keep a separate schedule for solution changes, usually every 7-14 days.