With over 22 years in the growing business, Logan McLean of Cool Springs Nursery joins Greg on the Row By Row Show tonight to discuss and break down the different types of seed starting mix (potting soil).
August is Greg’s least favorite month in the garden. With it being so hot in south Georgia, he is using this time to prepare for his fall garden with his silage tarps. Tarping, bed prep for the fall sweet corn crop. His first crop of cabbage and broccoli started in the greenhouse. Greg recommends starting varieties in the Brassica family (Broccoli) inside, if you plant start them in the greenhouse and have temperatures that reach in the 100s, you could have problems; he also states that there is still time to plant cover crops and flowers!
Potting Soil Ingredients
Most of the consumer mixes that you buy in the big box store are mostly made up of Peat, which is a very common ingredient in potting soil. There are different grades of peat; the best peat to use is peat that comes from Canada, they have the superior product. Peat with a good water holding capacity is the best.
Perlite is a volcanic glass that is heated at 1,600 degrees Fahrenheit. Whereupon it pops much like popcorn and expands 13 times its former size, resulting in an incredibly lightweight material. More porous than vermiculite. It is considered non-organic. It does drain well, and there are different grades. A lot of commercial growers use perlite to put on top of the seeds/seedlings to retain moisture.
Vermiculite is a hydrous phyllosilicate mineral that undergoes significant expansion when heated. Increases water, nutrient retention, and aerates the soil; it is heated just like Perlite. The finer the grade of vermiculite, the lower the quality – which is normally what consumers receive. The commercial line isn’t as fine as what the consumer would get. This mineral has major water holding capabilities. The nutrients in Vermiculite are not as good as what is in peat; vermiculite is used for aeration in your soil.
DIY Seed Starting Mix
A good mix should be dense enough to hold the plant, allow for air exchange and water flow while retaining moisture, be free of pathogens and weed seed, and meet the need of specific crops and growing environments.
One of the most used ingredients in commercial mixes is pine bark because it is economical. Pine bark needs to be aged to work well; most “container” gardeners use this mix for tomatoes but will work with almost any vegetable or fruit grown in a container. Coir is another important ingredient, it is considered coconut fiber. A natural fiber extracted from the outer husk of coconut with a very similar water holding capacity as peat.
Logan describes their companies propagation mix as using mainly sand and pine bark. Some of the varieties they propagate will have some perlite but not much. Having a mix with a good amount of pine bark and sand will help hold in moisture extremely well. Sand is used to increasing density and drainage, it is used as a filler. Logan’s container mix is made up of 80% pine bark, 10% sand, and 10% peat. We do add a small amount of 3-4 month fertilizer (8 lbs per yard) which gives it a kick-start. You normally want to keep your PH level around 5-6%.
Compost adds nutrient value and micros while holding water and nutrients well, has a high cation exchange value. Most mixes are 2 parts peat, 1 part perlite, and 1 part vermiculite.