As a newbie gardener, I am confused between gardening and potting soils as sold in the stores. Obviously, plants can grow in gardening soil, so why it can't or should not be used in a pot? What's the difference?
You're not supposed to use either potting or gardening soils in containers. Containers require a potting mix (big difference) because a container is a closed environment which is very unlike growing plants in mother earth.
For more info on this see this article on the gardenweb website in the container gardening forum. Around 4 years ago I read this and switched my container garden to a pine bark based potting mix which I make myself. This article is still generating comments and questions all these years later.
Thanks, but what is potting soil for if not for plants in the pots?
I was looking forward to your getting a variety of answers. I'm no expert but I use potting soil for house plants and plain old cheapest bagged topsoil for my container grown tomatoes, peppers, eggplants and cucumbers.
I found nothing better than home-made potting soil. Not exactly sure what is in the bagged products, but these bags (including Miracle Grow) are not consistent. Bagged soil should be heated to kill insects, mold and bacteria. I heat mine to 300 degrees.
Potting soil is a mix, all soils are a mix... those labeled potting soil are generally a lighter less dense mix that enable more air to reach the roots in a confined space of a pot. But regardless, you can and should amend all soils to best suit what's planted... you shouldn't use the same soil mix to pot cacti and violets. And remember to repot often and use fresh soil.
Many bagged soils, composts, mulches, and manures are clearly labled either "sterilized" or "nonsterilized", the sterilzed costs a few pennies more but I'm not about to waste fuel cooking many cubic feet of soil at home, nor am I willing to spend my time and energy at so frivolous a task when I can buy soil already sterilized so inexpensively. And I've found the national brands to be reasonably consistant, as consistant as any claimed to be custom mixed at some local nursery.
180F (internal temp) for 20 min. will sterilize the soil. I usually sterilize in 2 - 3 quart quantities (without internal thermometer) for 30 min.
While you can certainly grow all those plant using plain old topsoil in a container, your plants will do much better with a properly structured container mix. When I started gardening in containers I used topsoil and for the most part things grew. Then one year we had a very hot summer and bad drought and I had all kinds of problems with all my plants due to what the plants grew in. The next Spring I researched what I could do to improve the garden and ran across that article. After changing to that mix my plants grow a lot better now and much more resilient to environmental extremes.
I would suggest going to part 1 of that article (the link I pointed to was part 8) and read the comments because there is a lot of technical addendums there. I don't use the exact formula suggested in the article, I settled on a modified version. Due to the size of my container garden (> 200 cu.ft.) and that it sits on top a 2 story roof, it is impractical to replace all that mix every year. So I need to recycle mix from year to year. My formula is:
2 parts pine bark fines (it has to be the very small pine bark mulch which can be hard to find) 2 parts year old mix 1/2 part perliteThe pine bark and perlite provide structure to the mix so that it has lots of air pockets for the roots to grow and breath, drainage so that water doesn't pool and drown the roots, but not too much drainage so that it dries out too fast after watering.
Not really much of a bother, almost like making a cake.
I use this one often for most house plants
------------ Soil Recipe
4 cups soil 4 cups peat moss 2 cups vermiculite 6 teaspoons agriculture lime (powdered calcium carbonate)Most important do not use dehydrated lime. (It will raise pH to over
10 and plants won't survive.)Procedure is to mix all ingrediants. Add about half cup of water if mix is dusting and push through a screen. Place in a baking dish, wet it down with water and bake at 300F for an hour. Push through a screen.
Yield: 3 quarts.
------------
For larger amounts, sterilize separate containers of soil and peat moss and mix together when needed.
"Phisherman" wrote > Not really much of a bother, almost like making a cake.
There is no reason to steriliz vermiculite and lime, probably not peat moss either.
I think it's retarded to sterilize potting soil oneself when it can be readily purchased at mere pennies more than nonsterilized... there is no way one can bake dirt in their home oven for less money than the branded potting soil companies can process theirs by the freight car load, it's not possible to ignore the economies of scale. And once a plant is potted the soil is no longer sterile anymore anyway, in fact as soon as you handle that cooked dirt it's no longer sterile. As far as insects, they will probably seek out sterile soil quicker than nonsterile. It's really not necessary for potting dirt to be sterile... actually it's just a marketing gimmick.. plants grow outdoors just fine in ordinary everyday dirty dirt.
The key, I think, is selecting a national brand of potting mix that you like. Between brands there may not be much consistency, but within brands, there is.
The original question also was about garden soil. Whatever it is, it's not for potting. National brands may have some consistency, but don't count on it.
Soil from one garden to another is not consistant... that's why amendments are added. I do composting so for potting soil I blend it with various amendments depending on for what type of plant. And I don't worry about sterile soil or it containing insects because I keep no potted plants indoors... with six cats house plants are not a possibility. Where I live (Catskills) there are many lakes and ponds so there are people whose sole income is derived from dredging the rich black humous that acumulates in these bodies of water and sell it. I buy a 6-8 yard load once a year to work into my vegetable garden and beds... price varies with fuel prices but is typically $20/yd with a minimum 6 yd delivery. This is the same product labeled top soil sold in 40 lb bags sold at the big box stores and nurseries for about $4. The quality of bagged soils varies greatly by where one lives... I'm sure you won't find this kind of ultra rich top soil in the more arid regions. The upper Hudson River valley contains some of the richest soil on the planet.
: remember to repot often and use fresh soil.
Repot how often? Is the old soil good for anything, eg, as topsoil in the lawn/garden, or should it be just discarded?
I use spent potting and seed raising mix on my lawn to patch parts of it from time to time. I sieve out the big stuff and bung that on a garden and then use the finer stuff to seed new grass in to. Works fine.
rob
Depends how quickly the plant outgrows its pot, you do not want your plants to become pot bound. My general rule is to repot once every 1-2 years... the organic matter breaks down so the soil compacts.
No matter where you discard spent potting soil it will end up as dirt somewhere on the planet so you may as well sprinkle it in your yard.
I use spent potting soil mixtures to mix into my compost pile. Everything here is recycled. Nothing is wasted that can go into the gardens.
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