Wednesday, March 22, 2023
March 22, 2023

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Gardening With Allen: Use quality potting soil on plants


I replanted several of my indoor plants a month ago into larger pots and there is almost no new growth. I used a cheaper unfamiliar potting soil. Do you think that could be the problem? Should I replant them using better soil?

Indoor plants do not make a lot of growth this time of year because of low light. Recently transplanted plants usually develop some new roots before they make top growth. However I would expect a little top growth after a month. I would suggest that you tip a plant out of its pot and check for new roots growing into the new soil. If you don’t see some vigorous new root growth, it may be best to replant using some better potting soil. Make sure to remove all the poor soil.

Potting soil should have four main qualities: good water infiltration, good drainage, good water and nutrient holding capacity, and good aeration or air holding capacity.

Water should continue to quickly infiltrate into good container soil weeks after plants are established. Water should also 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 air holes than ordinary soil. These holes temporarily fill with water, and then gradually release the water leaving plenty of air holding capacity. These same materials also hold onto nutrients (fertilizer) that is added to the soil. I like to add water-holding crystals such as SoilMoist to help retain extra moisture.

Many potting soils also have fertilizer added. Some have only enough for two or three weeks. Others contain slow-release fertilizers that may last up to several months. Read the labels carefully to see if and how soon additional fertilizer should be applied. Plants in containers use much more fertilizer than those growing in the ground.

I avoid using “cheap” potting soils. I prefer nursery brands prepared by or recommended by a full-service nursery or garden store. If I buy some potting soil I am not familiar with, I like to put some in a pot and check the infiltration and drainage before I use it for planting. Black Magic and Miracle Gro are good national brands.