Issue: April 15, 2006

Mushrooms in potting soil | Prune lilacs now

Mushrooms in potting soil


Why are mushrooms growing in the soil (commercially purchased potting soil) in which I planted geraniums? Is this a sign of overwatering or a lack of humidity?

- Anna Victoria R.


Excessive soil moisture from overwatering may contribute to the problem. However, there can be mushrooms in potting soil even if you don't overwater.

Most commercial potting soils contain compost. The compost may be from many sources, but in every case fungi are part of the composting process. If the compost was properly made, the fungi should be no problem. The fungi in the potting soil should not infect the geraniums. The fungi are just continuing the process of decomposing the organic material in the soil to form humus and humic acids. If the soil was not properly heat treated during composting or afterwards, the quantity of active fungi will be very high. When the potting soil bag was opened new fungi could have been introduced to the soil. It would then reinfest, and fungi can grow in the potting soil.

In order for the development of mushrooms (fruiting structures of some fungi) a large mass of fungi must grow. High levels of soil moisture contribute to mushroom development. Garden geraniums are succulent plants (fleshy stems storing water). They can tolerate drying between irrigations. You can reduce the growth of fungi and development of mushrooms in your potted plants by allowing some drying.

Lack of humidity should not cause development of mushrooms. Since the geranium plants are succulent, they are less affected by dry air than many other plants.

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Prune lilacs now


My lilacs are blooming now. When can I prune them?


You can begin pruning now by cutting flowers to take indoors. In this manner, you will begin your pruning and have the fragrant flowers to enjoy in your home or office.

Lilacs and other spring blooming shrubs are those that are best pruned after they flower in the spring. If you wait until fall, you will cut off the blossoms that form in late summer.

After flowering has ended and the flowers have faded, you can prune away any flowers that you did not cut for indoor enjoyment.

If you need to remove large stems, that can also be done after flowering finishes. However, to minimize plant stress, you can prune large branches in the winter. Any buds cut at this time will not flower, but there should be many others left on the plant for spring flowering. Rejuvenation by removing old, large stems results in production of more floriferous new branches for following years.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!