This is for AutoPot growers in the last two weeks before harvest who want to finish on plain water. In an AutoPot, water and nutrients travel up from the tray the whole run, so the finish goes the same direction: plain water comes from the reservoir, and nothing gets poured through the top. The switch takes one refill done carefully.
The short answer
- Switch the reservoir to pH-stable plain water 10 to 14 days before harvest.
- Never pour water through the pots, not even once at the end.
- Empty what's left of the old feed, then open the flush taps until the lines run clear.
- Growing food crops? AutoPot says you can skip the plain-water finish entirely.
Do you need a plain-water finish at all?
| Your situation | AutoPot's guidance |
|---|---|
| Food crops | Flushing isn't necessary. |
| Other crops on mineral nutrients | Supply pH-stable plain water from the reservoir for the last 10 to 14 days. |
| Organic nutrients | Flushing isn't really considered necessary, since organics produce far less in the way of salts. |
| Pot feeding (nutrients in the soil, plain water in the tank) | The reservoir already runs plain water, so there's nothing to switch. |
Why the top stays off-limits
In an AutoPot, the plant draws water and nutrients up from the tray, so everything moves upward through the pot. Any excess keeps moving up and collects in the top inch of the substrate as a crust of mineral salts. AutoPot says that layer does the plant no harm as long as it stays at the surface.
Pouring water through the top dissolves that layer and carries it straight back down into the root zone. AutoPot warns this can damage roots because of how concentrated the salts are, which is why a traditional top-down flush does more harm in an AutoPot than good.
The same logic rules out going back to top watering at any point once a plant is established. AutoPot lists three effects: the dissolved salts spike EC in the root zone, the moisture profile the roots grew into changes, and oxygen in the root zone drops.
Switching the reservoir instead keeps the irrigation rate the same as the rest of the run, so there's no overwatering and no pool of washed-out salts sitting under the pot.
Don't pour water through an established AutoPot, at harvest or any other time. That includes a quick rinse of the surface and any drench-type product; liquids for an established plant go in by tray feeding.
Switching to plain water
- Count back 10 to 14 days. Mark the date on the calendar from your expected harvest.
- Time it to a refill. Let the tank run down to its usual refill point, about a third left.
- Tap off and empty the leftover feed. Topping up a third of a tank of feed with plain water leaves you at roughly a third strength, not plain water.
- Rinse the tank and filter while it's empty. AutoPot's own changeover from feed to plain water cleans both before refilling.
- Refill with pH-stable plain water and let it settle 30 to 60 minutes. Targets are in why your reservoir pH drifts.
- Tap on, then open the flush taps until the water runs clear. Solution sits in the tubing until a valve calls for it, so this clears the old feed out of the lines before it reaches the trays.
The trays still hold their last fill of feed. The plants drink it down on the next cycle, and every fill after that is plain water.
During the last two weeks
Keep refilling at about a third left with plain water, using the same tap-off, settle, tap-on routine. If a plant needs a late supplement, it goes in by tray feeding, never over the top; the steps are in feeding an AutoPot.
After harvest, the full teardown is in keeping your AutoPot clean between runs.
Parts that fix this
-
pH and TDS meters
Confirms the refilled tank reads like your source water, not diluted feed.
-
pH adjusters
For bringing the plain-water refill to target before it settles.
Questions
No. When a grower asked AutoPot's support forum about this, the answer was simply to fill the reservoir with pH-correct plain water 10 to 14 days out and let the plants take up what's left in the substrate.
AutoPot's support forum says that on plain water, plants use up the nutrients left in the substrate and then begin to lose their color. That's the finish working as intended.
AutoPot's support says a top flush is only for extreme circumstances, and its alternative keeps the same direction of travel: plain water from the reservoir. Strength limits that prevent the problem are in feeding an AutoPot.
That depends on your system's draw in late flower, which is usually its highest of the run. Measure it with the method in how to size an AutoPot reservoir, and plan the refills into the calendar.