Since you are not a real gardener unless you grow something from seed, and since we are approaching seed-starting season, the one thing we all need is good starting soil. There are a few things to keep in mind.
First, there is a difference between a potting mix and a starting mix. The potting formulas are heavier and don’t drain as quickly. Sure you can use them to germinate things, but since you don’t want your seedlings to dampen off, it is better to use a starter mix which will drain better.
Second, since we want to be the most environmentally conscious gardeners we can, we need to consider ingredients and look for those that are the most sustainable and cause the least amount of damage to the environment.
So, the first thing to consider is what to use as a basic substrate. For my money, compost is the key. Not only does it have the right pH for starting plants, it retains moisture. Most important, compost contains the microbial community necessary to convert organic matter into nutrients for seedlings and to create soil structure. You can use your own or you can purchase a bag or two of organic compost (not “natural” which ensures nothing at all).
Some folks substitute coco coir for compost. This is the fibrous stuff that covers the nut of a coconut. It is becoming more and more sustainable as North American supplies are developed. Oddly, these fibers hold more water (and the nutrients it contains) than peat which is a good thing.
Next, you need to consider what to add for drainage and aeration. Peat comes from special wetlands and takes hundreds and hundreds of years to replace. The new, thinking gardener no longer uses peat moss for anything. It is mined, and its production isn’t sustainable.
Traditionally, perlite and vermiculite have filled this role are added to these mixes. These are minerals, heated and expanded in size. They are not made with chemicals, but both are mined, which is a downside (though we have almost unlimited supplies).
Vermiculite is a mica-like volcanic glass that is super heated until it pops. It used to be mined along with asbestos so it really wasn’t safe. The short story is if you want to use it today, make sure it was manufactured post-1990, and only U.S. made. You don’t want to inhale asbestos fibers. Better to skip it altogether.
Then there is perlite, also mined and heated. It is natural but not very biodegradable, and its water retention and drainage properties will last after the plants are transplanted. This bothers some, though if I had clay soil I might want the extra drainage.
Anyhow, since the coir and compost will hold enough water for your seedlings, all you really need is drainage. For the money, sand works great. Sure it makes containers heavier, but come on! Or, you can use rice hulls if you can find them.
A good starting mix is one part coconut coir, one part sand or rice hulls and one part compost. If you think your compost is too “heavy,” add more sand or add more coir and less compost. This is one area where you are allowed a bit of “art” since your ingredients follow the science.
The bottom line is you can buy seed-starting soil and there are plenty of different kinds out there. It makes sense to look at ingredients, however, and it makes even more sense to make your own. Either way, the seed germination season approaches.
Jeff’s Alaska Gardening Calendar
Alaska Botanical Garden: It is time to join. This is a must for area gardeners. Lots of benefits for very little cost.
Spring Garden Conference: It runs from March 8-11. Make reservations now while you can. This event always sells out. Again, it is another must-do event.
Houseplants: Clean yours up