Article: How to Run a Pour-Through Test: EC and pH Monitoring for Container Crops
How to Run a Pour-Through Test: EC and pH Monitoring for Container Crops
Most nutrient problems in container production start quietly: root-zone salts creep up during a dry stretch, pH drifts as a feed program runs its course, or one irrigation line delivers less water than the rest. By the time leaves show it, the crop has already lost ground. The pour-through test is one of the simplest ways to catch these shifts early. It measures the electrical conductivity (EC) and pH of the solution draining from a container, right on the growing floor, without pulling media or waiting on a lab.
This guide follows the procedure published by North Carolina Cooperative Extension in The Pour-Through Extraction Procedure: A Nutrient Management Tool for Nursery Crops (LeBude and Bilderback, NC State University), which builds on the method first developed by Dr. Robert Wright at Virginia Tech. We have paired each step with the meters, calibration solutions and supplies available on BLACK LABEL.
Key takeaways
- Sample 30 minutes to 2 hours after a normal irrigation, and collect about 50 mL (1.7 oz) of leachate per container.
- Calibrate pH with both pH 4 and pH 7 buffers, and EC with a conductivity standard, before every testing session.
- Test your irrigation water at the emitter too, and subtract its EC from the leachate reading.
- Use the same flagged containers each time and log every reading, so you are tracking trends rather than one-off numbers.
How the pour-through method works
EC rises in proportion to the dissolved salts in a solution, and in a fertilized container most of those salts are nutrients. Measuring EC therefore gives a quick read on how much fertilizer is available in the root zone, while pH tells you how available those nutrients are to the plant.
After a container is irrigated to capacity, a layer of saturated solution (the perched water table) sits at the bottom of the substrate. Gently pouring a measured amount of water over the surface pushes that solution out of the drainage holes. Because it has been in contact with the whole root zone, the leachate gives an average picture of the nutrient solution the roots are working with.
The Extension guide also describes a tipping method: 30 to 60 minutes after irrigation, tilt the container to drain leachate from the bottom holes without adding any water. Both methods give accurate, averaged readings, so pick the one that suits your containers and crew.
What you will need
- pH and EC meter, or a combination unit. A portable meter such as the Hanna GroLine Waterproof Portable pH/EC/TDS/Temperature Meter Kit suits a daily scouting route; pocket testers like the Hanna GroLine Combo pH/EC/TDS/Temperature Tester, GroStar GS4 pH/EC Combo Pen or Bluelab OnePen are easy to hand out to multiple team members.
- pH 4 and pH 7 calibration buffers. The Extension guide recommends keeping both, since irrigation water often sits near pH 7 while leachate can run much lower. Single-use pH 4.01 and pH 7.01 buffer sachets make field calibration quick.
- EC calibration standard, such as 1413 µS/cm (1.41 mS/cm) sachets.
- pH electrode storage solution to keep the probe hydrated between sessions, such as GroLine storage solution sachets.
- A shallow tray or plant saucer to catch leachate.
- A calibrated measuring cup or graduated cylinder for the pour-through water.
- A small, narrow vial that holds about 50 mL and is deep enough to cover the probe sensors.
- Flags, a notebook or log sheet, and optionally a coffee filter to strain out bark and debris.
Step-by-step: running a pour-through
- Choose and flag your sample containers. Work across each block in a diagonal or X pattern: three to five plants for a block, seven to ten for a full irrigation zone. Test the same flagged containers every time so your data shows a trend.
- Irrigate as you normally would. Sample after a regular irrigation event, not a hand watering, so the reading reflects what the crop actually receives. Containers should reach capacity, with roughly 10 to 20 percent leaching.
- Wait 30 minutes to 2 hours for the container solution to equilibrate.
- Set each container in a shallow saucer, raised about half an inch so it drains freely.
- Pour water evenly over the substrate surface. Use your irrigation water and the volume in the table below. Larger containers, substrates that hold a lot of water and containers that were not fully irrigated need more.
- Or use the tipping method 30 to 60 minutes after irrigation, draining leachate straight into a collection vessel.
- Transfer about 50 mL of leachate into your vial, filtering out debris if needed.
- Calibrate your pH and EC instruments with fresh buffers and standards, following the manufacturer's instructions.
- Read and record pH and EC for each container.
- Keep a running log by crop and irrigation zone across the season.
| Container size | Water to pour | Leachate to collect |
|---|---|---|
| 1 gal (about 4 L) | 4 oz (120 mL) | 1.7 oz (50 mL) |
| 3 gal (about 12 L) | 12 oz (350 mL) | 1.7 oz (50 mL) |
| 5 gal (about 19 L) | 20 oz (600 mL) | 1.7 oz (50 mL) |
| 7 gal (about 27 L) | 30 oz (825 mL) | 1.7 oz (50 mL) |
| 10 gal (about 38 L) | 40 oz (1,200 mL) | 1.7 oz (50 mL) |
| 15 gal (about 57 L) | 60 oz (1,775 mL) | 1.7 oz (50 mL) |
| 25 gal (about 95 L) | 100 oz (3,000 mL) | 1.7 oz (50 mL) |
Volumes adapted from NC State Extension; conversions are rounded.
Calibration and meter care
Small differences in pH or EC can mean large changes in nutrient availability, so calibration is not optional. The Extension guide recommends calibrating before each use, and rechecking between samples if a reading looks off or you are making a significant feed or irrigation decision from it. Calibration takes a few minutes and saves time by eliminating guesswork.
- Use fresh buffers and standards each time; single-use sachets avoid contaminated stock.
- Check whether your meter compensates automatically for solution temperature, and follow its manual for anything it does not handle.
- Replace batteries before they fade.
- Keep the pH electrode wet in storage solution rather than letting it dry out. Glass electrodes lose sensitivity with age; when one will no longer calibrate to the buffers, replace it. Some pens, such as the GroStar GS1, take a replacement electrode rather than a whole new unit.
- Keep the kit where your scouts work. If it rides in a vehicle, an insulated cooler protects it from temperature extremes.
Follow the product label and SDS when handling calibration, cleaning and storage solutions.
Reading the results
Units. Meters report EC in different units, but most convert directly: 1.0 mS/cm equals 1.0 dS/m, 1.0 mmhos/cm and 1,000 µS/cm. Know which unit your meter uses before comparing numbers between instruments or against a target.
Targets. For woody nursery crops in bark-based media, the Extension guide gives a leachate EC range of 0.5 to 2.0 mS/cm during active growth and a leachate pH range of 5.2 to 6.3. These figures are specific to that production system. Rockwool, coco and other substrate programs run to different targets, so use the ranges set by your nutrient program, substrate manufacturer or crop consultant, and treat pour-through data as a way to see how far you are from them.
Subtract the water. Irrigation water carries its own EC and pH. Sample it from an emitter or nozzle just before it reaches the crop, not from the pump or the surface of a tank, and subtract its EC from the leachate reading to see what is coming from fertilizer. The guide also recommends a full laboratory analysis of irrigation water once or twice a year, and sending leachate to a lab at least once per season to check your meter readings against actual nutrient levels.
Turning readings into decisions
A single pour-through reading is a snapshot; a season of readings is a management tool. Some operations test weekly and use the results to plan the following week's irrigation:
- EC trending high: increase irrigation volume (or lengthen the final irrigation of the day) to leach more salts.
- EC trending low: reduce irrigation volume to hold nutrients in the root zone, and review whether fertilizer has run out or is being leached too fast.
- Big differences between containers in the same zone: look at irrigation uniformity first. A clogged emitter or nozzle shows up as an outlier.
- pH drifting over time: pH can fall as calcium, magnesium and micronutrients are used up, or rise toward the irrigation water's pH as the substrate loses buffering capacity.
- Chlorotic or off-color foliage: pair a pour-through with a leaf tissue sample to separate a nutrient problem from a disease.
Graphing average EC and pH by zone across the season shows when fertilizer is used up, whether irrigation volume is too high or too low, and where uniformity needs attention. For more on using irrigation to manage the root zone, see our post on crop steering through irrigation.
FAQ
How often should I run a pour-through test?
Pick a regular cadence and stick to it; weekly is a common rhythm for operations that use the data to plan irrigation. Consistency matters more than frequency, so test the same containers at the same point after irrigation each time.
Is the tipping method as accurate as pouring water through?
According to the NC State Extension guide, both methods give accurate, averaged readings of the root-zone solution. Tipping skips the added water but works best 30 to 60 minutes after irrigation, so it suits smaller containers that are easy to lift.
Which calibration solutions do I need?
At minimum, a pH 4 buffer, a pH 7 buffer and an EC standard in the range you measure, such as 1413 µS/cm. Add electrode storage solution and cleaning solution to keep the pH probe in good condition.
Why test my irrigation water separately?
Source water adds its own salts and can shift substrate pH over time. Subtracting the water's EC from the leachate reading shows how much of the root-zone EC is coming from your fertilizer program.
Source
LeBude, A.V. and T.E. Bilderback. The Pour-Through Extraction Procedure: A Nutrient Management Tool for Nursery Crops (AG-717-W). North Carolina Cooperative Extension, NC State University.
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