Question
I read the answer about indoor potting soil (Miracle Grow and Peters Special also) that repel water because of the high peat content.  I have several indoor plants whose instructions are to let them dry out almost completely before watering.  My question is:  Is there something that I can add to these potting soils that will help prevent the caking and water repelling?  I have heard of "surfactant" to add but have no idea of a brand name and haven't seen anything in my local garden shop that specifically says that it's a surfactant.

Thank you,  Doug

Answer
Hi Doug,

I was not the one who expressed concern about peat-based potting mixes repelling water.

For most houseplants, peat-based potting mixes are preferred because peat not only absorbs water and releases it slowly to the roots, but it also has millions of tiny air pockets to supply oxygen to the roots. Peat moss is also lighter and cleaner to use.

It is true that when peat-based potting mixes get completely dried out, they are difficult to re-wet, much like a sponge that gets dry and hard and water repellent. However, there are no plants that you should be using peat-based potting mixes with that should ever get that dry. If the soil gets that dry, then the roots will be seriously damaged by the drought. So the best way to prevent "caking and water repelling" is to not let the potting mix get so dried out.

Succulent and Cacti potting soil does need to get almost completely dried out, so peat-based potting mixes are not appropriate for these types of plants.

Many peat-base potting mixes do incorporate wetting agents that make it easier to re-wet dried peat mixes. If you do a search under "soil wetting agents" you will probably find some brand names and sources for them, although I don't think they are necessary.

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

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