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
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
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
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.
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.
Not really much of a bother, almost like making a cake.
I use this one often for most house plants
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
Yield: 3 quarts.
For larger amounts, sterilize separate containers of soil and peat
moss and mix together when needed.
There is no reason to steriliz vermiculite and lime, probably not peat moss
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,
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
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.
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
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 perlite
+ fertilizer (depends upon the plant this mix supports)
The 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.
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.
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.
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.
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