Potting soils and seed-starting mixes for your garden
Healthy garden vegetables and flowers begin with good soils.
March 1, 2013 - Author: Gary Heilig, Michigan State University Extension
March is the month when smart gardeners gear-up for the growing season by starting vegetable and flowering seedlings. One important factor that will determine the degree of success is the potting media.
All seed-starting mixes and potting soils are not created equally. As you visit area garden centers you will see products such as Miracle Grow, Scott’s, Farfard, Schultz, Happy Frog, Hyponex and others. Experienced gardeners generally have their favorites, while beginners may be at a loss as to what potting media to select.
According to Michigan State University Extension, there is a difference between potting soil and seed-starting mix. Soilless seed-starting mixes have a finer texture and are made from ingredients such as milled peat moss, perlite, coconut coir fiber and vermiculite. Although potting soils may be used to start seeds, they tend to have a more coarse texture and may contain field soil, compost or composted manure along with vermiculite, peat moss or perlite. Some seed-starting or potting mixes may contain fertilizer as an additive. Read the package. Some products contain enough fertilizer to provide seedlings with sufficient nutrients to last up to three months, while others may have no added nutrients.
Although most soil mixes contain some peat moss which absorbs and helps retain moisture, some manufacturers add moisture retention granules to their soil mixes that expand many times their size as they absorb water. These are especially beneficial for container gardening during dry weather or when you forget to water your plants. When potting soil ingredients include field soil, compost or manure, they may also contain some weed seeds. Although this may be an inconvenience, few seeds will be viable if the soil has been pasteurized.
Organic gardeners prefer to use organic potting media, but be aware that the term “organic” on the package does not mean that the mix would be acceptable for starting organic seedlings. Read the package closely to determine if the soil and other additives are approved for organic production.
For smart gardeners hoping to save a little money, making your own seed-starting or potting mix is an option. I like to mix one-third part spaghnum peat moss or coconut coir fiber with one-third part finely screened compost and one-third part vermiculite. Add about 1 to 2 cups of worm compost to a 5 gallon bucket of your soil mix. I also like to stretch commercial potting media by adding up to 50 percent screened compost. I generally use this mixture when transplanting seedlings into larger pots.
When I purchase commercial potting media, I like to select those that have a guarantee. To me, a guarantee indicates that a company is willing to stand behind their product. Keep the sales receipt just in case you are not satisfied with the performance of the product. It is generally required to obtain a refund.
Visit my online class for more additional information on growing seedlings (high speed internet connection is required).
For more information on a wide variety of smart gardening articles, or to find out about smart gardening classes and events, visit www.migarden.msu.edu.