The white filaments of the mold that breaks down fall foliage is called leaf mold by gardeners.

You can actually see this magical stuff hidden in moist piles of old leaves. Leaf mold has the ability to act as a catalyst making nutrients in your soil more available for use by plant roots. Think of it as the superhighway that transports nitrogen, phosphorus and potassium from your soil to the plant to stimulate growth.

How to make leaf mold

Simply rake or blow fallen leaves into a pile and secure with a wire cage or weighted piece of plastic to keep the winter wind from blowing the leaves about. If the leaf pile is sitting on top of soil, then the leaf eating critters will soften and rot the leaves from below. Once late spring arrives the rotted leaves in the middle of the pile will have the white filaments that mean they are partly rotted and ready to spread as a mulch around trees and shrubs or as an additive to old potting soil.

Tip: I drop leaf mold clumps on top of emerging young weeds in the spring. This blocks sunlight and smothers the weeds (like shotweed) before they can flower and set seed.

Or stuff those leaves into plastic garbage bags…

If you lack room for piles of fallen leaves fill up garbage sacks with maple leaves, add a shovelful of soil to the bag and poke holes all over the plastic covering to allow air into the rotting process. You can store the bags of fallen leaves under outdoor furniture or inside a shed or garage until spring. Then add the moldy leaves to old potting soil or around shrubs.

You mean you can reuse potting soil?

Yup, with the magic of leaf mold or a shovel of compost old potting soil that is dry looking but full of white chunks of perlite can be reactivated for use and replanted with annuals and other container plants. The trick is to add just enough leaf mold to moisten and liven up the old potting soil but not too much as to interfere with the quick draining action of the potting soil. Too much organic matter such as compost or leaf mold can block drainage holes in pots and encourage root rot. Mix the leaf mold thoroughly into the old potting soil stirring it up so that it becomes the consistency of fresh potting soil. Light enough to drain well, but rich enough to hold moisture.

Tip: If you have a lot of containers full of last summer’s potting soil wait until spring and dump all the potting soil onto a tarp. Then add shovels of leaf mold stirring it into the old potting soil with a hoe or rake. Once it looks fluffy but not dense refill your containers with the refreshed potting soil and plant.

These plants love leaf mold the most…

Hydrangeas, begonias, fuchsias, ferns, impatiens, lobelia, hosta, brunnera and heucheras thrive in leaf mold enriched soil because they need moist soil rich in organic matter to perform best. Trees, shrubs and annuals that do great in the shade are the same plants that will appreciate leaf mold on top of the soil or worked into their potting soil.

Some plants like fast draining soil so don’t add too much organic matter…

Lavender, sedums, succulents, salvias, sage, thymes and many other Mediterranean plants prefer a lean soil that drains quickly. Don’t waste your compost or leaf mold on these low water use plants.

Marianne Binetti has a degree in horticulture from Washington State University and is the author of “Easy Answers for Great Gardens” and several other books. For answers to gardening questions, visit plantersplace.com and click “As The Expert”. Copyright for this column owned by Marianne Binetti. For more gardening information, she can be reached at her website, www.binettigarden.com.