PourThru: Leachate from the Pot as a Sample of the Root Zone Solution
The PourThru is a simple way to get at the solution the roots are standing in. You pour some distilled water on top of the pot and measure what runs out at the bottom. On its way through the pot this leachate has picked up the solution from the root zone. The plant stays in its pot, and all you need is a pH meter and an EC meter.
How it works
Water as usual and wait half an hour to an hour. Then pour distilled water evenly on top and collect the leachate underneath. For a pot of just under 4 litres that is about 150 ml, a little under a cup; for about 11 litres, 350 ml. About 50 ml should come out, enough to immerse the probe. Measure pH and EC in it. The method works in potting soil, peat, and coco.
What to watch
The readings depend on handling. A pot that has dried out shows a higher EC, while too much water poured on dilutes the sample and shows a lower one. So always measure the same way: same time after watering, same amount of water. The fact sheet gives no amount for larger pots; settle on one and stick to it. If you have several plants, measure several pots and take the average.
How to read the values
Compare pH with the range for your medium: 5.5 to 6.5 in peat, 5.4 to 6.2 in coco. For EC no target values for cannabis are established; as a rough frame, the fact sheet for ornamental crops treats 2.7 to 4.6 mS/cm as normal. The trend tells you more: if it rises from one reading to the next, salt is building up in the pot, and you let more water run through or flush with plain water. A reading below the frame points to too little fertiliser. Never mix two measuring methods, because other methods give completely different numbers for the same pot.
When to measure something else
In rockwool you measure the water that runs out of the slab anyway, and in hydroponics the solution in the tank. The PourThru is not needed there.