Soilless Media Sample Collection Guidelines
Soilless media (a.k.a potting "soil") can be tested pre-plant (in bulk) or post-plant (in container). Media should be tested periodically throughout growing season or whenever problems arise.
- Collect a representative sample consisting of 5 to 10 thoroughly mixed subsamples.
- Submit at least 1 quart (2 preferable) of the composite media sample in a clean, well-sealed plastic bag.
Important: Collect samples at the same time interval after irrigation or fertigation for more meaningful, comparable results
Pre-Plant Media Sampling
When: Collect samples before planting to determine baseline media parameters
How: Collect subsamples of bulk (pre-plant) substrates from the center of individual bags or from random areas in the central part of the stockpile.
Important: For accurate pH measurement, samples from dry substrates should be moistened before being sent to the lab. Add 1/3 to 1/2 cup water and knead in before submission. This will activate any lime present and provide more accurate pH results.
Post-Plant Media Sampling for Pots
Non-destructive sampling: Collect media from 5-15 pots under the same growing/fertilization conditions
Small Pots: Remove root mass from pots and pinch a section of media from the middle section of each root mass
Large Pots: Brush aside top 1" of media and use a probe or trowel to collect the substrate from the center of several pots
Destructive sampling: Collect media from 5-15 pots by removing the root mass and shaking pots to remove loose media.
Post-Plant Media Sampling for Flats
When: Post-plant soilless media testing of flats is used to diagnose seedling growth problems
How: Separately collect media from "Good" and "Bad" flats. "Good" flats resemble good germination and growth, "bad" otherwise. Collect 1-2 quarts from several cells and different flats.
Bulk Density Sampling
Bulk Density testing (BD) is available as an additional test for soilless media.
How: Collect subsamples from the center of individual bags or from random areas in the central part of the stockpile.
Amount: BD testing requires at least one half-gallon of media.
Important: Two bags of media should be submitted for bulk density testing. One bag for the standard analysis and one for bulk density. Write "BD" on one bag.
This page was last modified on 11/02/2026