Have you ever wondered what the difference is between seed starting mix and potting mix? They both hold moisture and have good drainage to allow roots to develop. They are most commonly made from different combinations of aged bark/forest products, sphagnum peat moss, coconut coir, perlite and/or vermiculite. They are both disease and weed seed free.
The main difference is their purpose.
The purpose of seed starting mix is to give the seed a place to germinate, or develop into plants by putting out its first roots and shoot. Seed starting mix is finely textured so that the seeds make good contact with the mix. The finer texture also keeps the seeds from falling down into bigger spaces in the mix where they would have a hard time germinating. Another difference is that seed starting mixes usually have little nutritional value for the emerging plant. The seed has enough stored food to reach the point where it can begin to grow leaves. After roots and shoots have started growing it’s customary to move seedlings into potting mix.
The purpose of potting mix is to support the growth of the seedling or provide a place for plants to continue growing. Potting mix can be less finely textured. Potting mix will often have nutrients added to support growth ranging from man-made fertilizers, kelp, bone meal, blood meal, greensand, vermicompost, compost and more. The main point is that you want to provide low levels of nutrients such as nitrogen, potassium, phosphorous, calcium and magnesium while keeping soluble salt levels low and pH between 5.5 and 6.8. If nutrients aren’t added to potting mix then they will have to be added when watering using liquid fertilizers or natural teas for plants. Learn how to make vermicompost tea.
Adding a good quality compost to potting mix will provide most of the nutritional needs. Microbes also slowly break down nutrients making them available to the plant over time. It’s also a useful addition to potting mix because it adds valuable microorganisms that help the plant fight off diseases. Compost will also help to retain moisture and prevent the surface from getting hard and repelling water from soaking in – hydrophobic.
Over time, the nutrients in potting mix will leach away and be used up by your plants. To provide nutrients you can water your plants with vermicompost tea, scratch in vermicompost under the drip line of the plant or pot up the plant adding 10% vermicompost to the mix.
I usually use potting mix to both start seeds and grow the seedlings. I always add 10% Devine Gardens vermicopost to the mix. When I buy potting mix I just buy what is conveniently in the store. I don’t buy anything with commercial fertilizers added. I also like making my own potting soil based on peat moss, vermiculite and Devine Gardens compost and vermicompost. I’ll make my potting mix available when I decide it’s good enough to share.
If you make your own potting mix or unsure about the mix you have then do a test. Just plant some fast-growing plants like lettuce, onions, cress or radishes. Watch what happens. Did most of the seeds germinate? Do they look healthy?
No matter what you decide to use, remember, have fun. Don’t get too stressed out. Do what is easiest and enjoy!