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GARDENER COLUMN: The “dirt” on potting mixes
SAUK COUNTY GARDENER

GARDENER COLUMN: The “dirt” on potting mixes

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“Land is not merely soil, it is a fountain of energy flowing through a circuit of soils, plants and animals.”—Aldo Leopold, author, philosopher, scientist and conservationist

I’m currently evaluating my houseplants and other plants to see which ones need to be repotted, divided, and potentially propagated. This means I must once again brush up on potting mixes or media to determine what type to use for my containers and indoor plants. You would think you could use plain ‘ole’ garden soil but that is not the case for container plants. Of course, that’s not a problem right now as the ground is frozen and there is no way I’m going to be able to dig some up anyway. This means if you don’t already have some potting media at home, you’re going to have to buy some. When you walk down the aisle at various stores, you’ll see a variety of different potting soil mixtures and components. In fact, when I went to a local store the other day, I saw potting soil, potting soil plus, peat moss, perlite, vermiculite, African violet mix, cactus mix, and orchid mix all on the same shelf. It was obvious what the African violet mix, cactus mix, and orchid mix were used for, but cactus mix is also recommended for succulents like hen and chicks. With so many options, how do you choose?

As I noted earlier, you don’t want to use ordinary garden soil for container plants. It’s typically too heavy to provide proper aeration, it doesn’t drain well, and doesn’t have the right nutrients. It also tends to have soil-born fungi, pathogens and insects or pests in it that aren’t good for your plants. Potting mix is a mix of different components – none of them should be actual soil – and is designed to have more nutrients to feed your plants and provide proper drainage and water retention. Some basic ingredients of most potting mixes or soils are sphagnum peat moss, bark, perlite, vermiculite, fertilizer, compost—or some other nutrient-rich organic materials, or coir. They might even include water-holding crystals, additional lime to adjust the pH levels, or a wetting agent. The main reason we use potting soil in containers is because of its ability to help a plant to have proper drainage.

You know you can’t use actual garden soil and you know you need some type of potting mix that’s free of actual soil, but now you have to choose which one. An all-purpose potting mix can be used for most houseplants and containers but you still want to assess them based on what your container plant or houseplant needs regarding nutrients and water. Also, consider their location. Plants that will be in shady or indirect light will not lose moisture as fast of plants located in full sun or near a sunny window. The goal is for your potting mix to provide proper aeration, have good water retention, not become waterlogged, and provide nutrients for your plant. Peat moss, coir, and bark will help retain water. Perlite helps provide aeration and water control. Vermiculate is similar but helps retain more water and fertilizer than perlite. Look for mixtures with more vermiculite if your plant is going to be in sunny or hot location—or consider adding it if needed. Limestone can help balance the pH level of peat moss. Compost and fertilizers will initially provide nutrients. Nutrients will need to be replaced as the plant develops and grows.

As pointed out earlier, some potting mixes are specifically designed for a particular type of plant. African violets like their soils slightly more acidic so an African violet mix has been developed to accommodate that particular need. If you have a lot of African violets, consider purchasing the mix designed specifically for them. If you only have one or two, you may use a general potting mix. Cactus mixes are designed so cactus and succulents have proper drainage to help prevent them from getting overwatered and developing root rot. If you’re starting seeds, use a soilless seed-starting mix to germinate and then transfer them to containers with all-purpose potting mix when they have their true leaves.

Read the potting mix bag’s ingredients if they are listed. If actual soil is listed, don’t purchase it for your containers. Look for ones that say they are sterile mix – they will be free of weed seeds, diseases and insects. Try to select one that is light when you lift it as that means it’s unlikely to include actual soil in it. Check out the soil amendments if listed. Some are organics, others not, so choose potting mixes based on your preference. If you need a lot of potting mix or have plants with specific needs, you may decide to create your own mix. Visit https://extension.psu.edu/homemade-potting-media to find a “recipe.” No matter what route you go, you’ll still have to add fertilizer and water regularly after you’ve planted to ensure happy, healthy plants.

For more information or gardening questions, the University of Wisconsin Madison Division of Extension Sauk County office at 608-355-3250 or email haley.weisert@saukcountywi.gov.

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