In-house sampling methods to monitor the growing media

Some of the most common problems in container production are associated with inadequate pH and EC levels in the growing media. Fortunately, many problems can be prevented by monitoring the growing media. Four in-house sampling methods are available to monitor pH and EC of container-grown plants in greenhouses:  Saturated media extract (SME), 1:2 Method, Squeeze Method and Pour-Thru.



Saturated media extract is the method commonly used in horticultural commercial labs. It is recommended for new batches of growing media, when sub-irrigating and for containers of any size. It can also be used for plugs, by collecting multiple samples. The downside of SME is that it is a destructive sampling method. The 1:2 method applications are similar to SME. However, the SME method is preferred over the 1:2 method because it is not affected by moisture variability or exact volume of the sample.

Pour-thru method is an excellent alternative to quickly monitor changes overtime. It is highly recommended for container production where it is possible to collect leachate and when using controlled release fertilizers. Plants irrigated with ebb-and-flood benches or flood floors tend to accumulate high level of salts on the top layer of the growing media. The pour-thru method may displace the salts to the bottom of the container and leach to the sample, providing inaccurate results. Therefore, avoid using pour-thru when sub-irrigating. Instead use SME or 1:2.

Plug squeeze is used for plugs or bedding plant flats.

Keep in mind that the reference numbers vary by method. For more information on interpretation of results go to: https://ag.umass.edu/greenhouse-floriculture/fact-sheets/current-methods-of-greenhouse-media-testing-how-they-differ

Sample analysis cannot be better than the quality of the sample. Consistency on how, when and who collects the samples is essential to track changes in the growing media over time.

Source: e-Gro

Publication date: 2/7/2017

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