Back to top

Greenhouse Updates: March 24, 2023

Keep an Eye on Substrate pH and EC
March 24, 2023

Iron deficiency in Calibrachoa (G. Njue) Conducting regular testing of substrate pH and EC is vital for healthier plants and successful plant production in the greenhouse. Perform regular soil tests so that you can identify problems early and take corrective action. It is also important to train staff to recognize nutritional disorders so that they can scout for nutritional disorders while working in the crop.

Checking plants weekly is the key to managing greenhouse nutrient problems. Check color and vigor of the foliage, as well as the health of the roots. Checking the roots is important because the plant may have a compromised root system due to Pythium, fungus gnat infestation or waterlogged and poorly drained media.

Regular testing of substrate pH and EC is important because pH affects the availability of nutrients and EC provides a picture of the overall concentration of fertilizer salts in the media. For plugs, test two to three times per week, because their smaller media volumes are more susceptible to changes compared to bigger volumes. For 4-inch pots, test once a week, and for containers 6 inches or larger, every two weeks.

As pH is concerned, for iron-inefficient crops (such as petunia, calibrachoa, pansy, nemesia, bacopa, dianthus, snapdragon, verbena and vinca), the acceptable pH range is 5.4-6.2. For iron-efficient crops, such as seed and zonal geranium, marigolds, New Guinea impatiens and lisianthus, the acceptable pH range is 6.0-6.6. For other crops such as impatiens, ivy geraniums, poinsettia and chrysanthemums, the acceptable pH range is 6.0-6.4. A range of 6.0-6.2 would be acceptable for most crops.

For EC, there are two in-house testing methods to choose from: the pour-through method or the 1:2 method ... refer to table below... saturated media extract tests (SME) for EC are also offered by testing labs. Select one method and stick to it, and establish a target range depending on your crop.

The acceptable EC ranges depend on the testing method and the crop:

EC (mS/cm)

Pour-Through method

1:2 method

Acceptable range

1.0 – 6.0

0.30 – 1.50


1.0 – 2.5

0.30 – 0.75


2.6 – 4.5

0.76 – 1.25

High fertility range

4.6 – 6.5

1.26 – 1.75

Can cause root damage

> 8.0

> 2.5


- Geoffrey Njue, Extension Specialist, UMass Extension Greenhouse Crops and Floriculture Program