University of Maryland Extension

Salinity Matters for High Tunnels and Growing Media: How to Interpret Salinity Test Results

High tunnels or hoop houses are popular season-extension tools used by urban farmers, vegetable producers, and cut flower growers.

One of the benefits of growing in a high tunnel is that it protects crops from excessive rain and keeps their leaves dry, which can reduce the spread of disease. However, soaking rains serve the beneficial purpose of leaching salt accumulated from fertilizers, compost and minerals in the irrigation water down below the root zone. Over time, a lack of soaking rains can result in a build-up of minerals in high tunnel soil, increasing the soil’s salinity. Sometimes a build-up of these minerals appears as a white crust on the surface of high tunnel soil.

Salinity is an important consideration for management of healthy soil and growing media, particularly in high tunnels or hoop houses. Electrical conductivity measures salinity, or the total amount of soluble salts or minerals in the soil or growing medium.

Salinity is also an important measure of the quality of growing media (mixes of substrates such as peat, coir, compost, sand, vermiculate, etc.). Some composts can have a high soluble salt content, so if you are mixing your own growing medium, or purchasing one, it is a good idea to make sure that the salinity of your mix is not too high.

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