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News / Life / Clark County Life

Gardening with Allen: Add water-holding crystals to help retain extra moisture in soil

By Allen Wilson
Published: April 27, 2024, 6:08am

Last year, I made my own potting soil by mixing about half peat moss with my garden soil. The plant I bought already potted grew much better than the ones in my own mix. How can I improve my potting soil?

Even good quality garden soil does not make good potting soil. It holds onto too much water and doesn’t drain well enough. There are four main qualities which potting soil should have; good water infiltration, good drainage, good water and nutrient holding capacity, and good aeration or air holding capacity. Water will continue to quickly infiltrate into good container soil weeks after plants are established. Water should also continue to drain from the bottom of containers within a few minutes after irrigation.

Putting soil in a container approximately doubles its water holding capacity. That is why outdoor soils do not work well in containers, or even in raised planter boxes. Plant roots need the oxygen in soil air to grow and thrive properly. Coarse, irregular materials like peat moss, perlite, bark, vermiculite and sponge rock contain many more and larger air holes or pores than garden soil. Large pores drain quickly and are filled with air. Smaller pores temporarily fill with water, and then gradually release the water as it is used by the roots. These same materials also hold onto nutrients (fertilizer) which is added to the soil.

I like to add water-holding crystals such as “Soil Moist” to help retain extra moisture. These crystals add water holding capacity without reducing air in the soil. Mix these thoroughly into the bottom two-thirds of the container. If placed too close to the surface, crystals tend to push themselves to the top.

Many potting soils also have fertilizer added. Some have only enough for 2 or 3 weeks. Others contain slow release fertilizers which may last up to several months. Read the labels carefully to see if and how soon additional fertilizer should be added. Plants in containers use much more fertilizer than those growing in the ground because some of it is leached out of the container every time it is watered.

Commercially available packaged potting mixtures vary widely in quality. I avoid using “cheap” potting soils. I prefer nursery brands prepared by or recommended by a full service nursery or garden store. Black Magic and Miracle Gro are good national brands.