Article Copied from the American Rhododendron Society Blog

Print date: 9/28/2023

pH - Why is it important for rhododendrons?

29 April 2023 @ 07:40 | Posted by Admin

What is pH? How do I obtain a proper pH for my rhododendrons?

pH refers to the acidity of a material. Technically, it is a measurement of the hydrogen ion content. The pH scale ranges from 0 to 14, pHs of 0 to 7 are acidic, pHs of 7 to 14 are referred to as being basic or alkaline. A pH of 7 means the material is neutral. For rhododendrons the preferred pH should be between 5 and 6.5.

It is difficult for a layperson to determine the pH of the potting medium they use. There are pH meters on the market, but the ones that cost less than $100 are practically worthless. However, it is fairly easy to get your growing medium pH in the desired range. Fir or hemlock bark is almost always in an acceptable range and, therefore, an ideal growing medium to use. It is best if the bark has decayed for six months prior to use.

The reason pH is important for plants has to do with the intake of minerals and nutrients. If the pH is too low, rhododendrons have difficulty taking in the nitrogen and phosphorous they need for growth. If the planting medium of soil is too alkaline, i.e. the pH is too high, it usually causes iron and/or manganese deficiencies.

In summary, pH is important for growing healthy rhododendrons. Generally, it is advisable to use fir or hemlock bark in pots and bark or pine needle mulch as an additive for plants grown in the ground.