How to turn forest soil into potting soil

AuGres, MI(Zone 5b)

We have 20 acres of woods on our property. The soil is black and rich from centuries of leaf composting. I was wondering if I could dig up some of this soil and treat it somehow to use for potting soil. I'd like to grow some plants inside and don't want to buy soil if I can somehow sterilize this soil.

Could it ever be made sterile enough to start seeds in?

Any guidelines would be most appreciated.

Indianapolis, IN(Zone 4b)

I dunno if sterile soil's what you want, actually. There are lots of good bacteria and fungi in there.

AuGres, MI(Zone 5b)

Are you saying that if I want soil for container planting next spring I can just go dig up some from the woods and put it directly into the container rather than buying potting soil from the store?

Also, if I want to start vegetable seeds indoors under lights I can use soil from the woods without heating it up to sterilize it in any way?

Thanks for responding.

Anne Arundel,, MD(Zone 7b)

I'll agree with the Pirate in that sterile soil may not be necessary. I have never sterilized for seeds and I do reuse soil sometimes.
The bigger issue with natural soil will be drainage. There's at least one long thread by tapla devoted to drainage in potting soil. Soil that holds too much water is a quick death.

Since you are asking, I assume you haven't done much seed starting. You'll probably be a lot happier if you spring a few bucks for seed soil in a bag and have better chance of success.
To use that soil in pots will still have drainage questions. Also probably heavier than commercial,,in case you' d have to move the pots at times.

AuGres, MI(Zone 5b)

I could lighten it up with some perlite for container planting couldn't I? That would help with drainage.

I used to do a lot of growing from seed till we moved up here. I always used the little blow up peat pellets. I'd get perfect germination with them. Once they got big enough I'm move them into white styrofoam cups with a hole punched in the bottom for drainage and I'd use potting soil.

I guess it won't hurt to try it. It's out in the woods and it's free for the taking. :)

Cincinnati, OH(Zone 6a)

Another issue with that soil is that it might come with lots of seeds- weeds, trees, natives, whatever grows in those woods. If you decide to do it, I wouldn't start off with lots of seeds which might be special to you. It might be better to do a couple of test runs and see how it works out.


Anne Arundel,, MD(Zone 7b)

Perlite sounds good--altho now I'm wondering how cheap the free soil is when you start investing in perlite. But you can give it a whirl. I'm all for experiments.!

Mid-Cape, MA(Zone 7a)

I found a couple sites that talk about using regular "dirt" to make potting soil. These give some recipes. It may seems like more trouble than it's worth, but according to the sites, it can be done!

AuGres, MI(Zone 5b)

Thanks so much. The links were helpful. I had to laugh at the last link though. In it's formula it stated "leaf mold" and when I clicked on "leaf mold" it popped up with a kitchen gadget site selling cookie molds in the shape of leaves. ha ha ha

I know it's easier to go out and buy soil but what happens if we can't do that any more for whatever reason? I want to learn to do things myself and be self sufficient. I'll have to ask the neighbor for some cow manuer and begin aging it. They have two cows.

I know the virgin soil from the woods is good dirt. We had a 70 x 300 pond dug and had the excavator take the top 20 inches of top soil and dump it on my vegetable garden area. I then had the 30 x 50 area fenced with an 8 foot fence to keep out the deer, rabbits etc. I've been able to grow the most beautiful produce free of disease and bugs etc. There seems to be a very good balance going on in there and each fall I try to put something back by dumping a 6-10 inch layer of dried leaves which we till in the next spring.

I have a lot of containers I plant annuals in each year. I'm thinking of cutting back on them because of the cost of buying the potting soil and the plants. If I can learn to make my own potting soil and grow my annuls from seed it would help with the budget now that we're retired. Potting soil is very expensive when you have to buy many bags of it. I don't like to reuse much of it because the plants take so much out of the soil each year.

I'm sure there will be weed seeds. I'll deal with them in the containers. I will probably use the outdoor grill to heat the soil up to 180 degrees although I'm not sure why that is necessary. Many wilflowers grow in virgin soil in the woods just fine. How would the requirements for annuals be much different?

It's all a learning experience. Thanks for the help.

Anne Arundel,, MD(Zone 7b)

Now that I understand better why you want to do it and that you're an experienced gardener after all LOL, just adding this- I would not bother to sterilize it. You can deal with weeds in containers easily. You can weed your seedlings if you use it for seeds too. As for drainage, when I bought a bag of highly recommended Fafard soil, I was surprised at how chunky it seemed. After reading on DG I understand why. I also found that a few cannas I bought last year were grown in basically sand plus wood mulch (probably courtesy of Katrina etc) So I've been using a finely ground old-wood mulch in my potting this year ---courtesy of my neighbor cleaning up old sticks and bark around his old woodpile and chipping it--- and it seems to be working OK.

Cincinnati, OH(Zone 6a)

The purpose of heating is to kill pathogens and seeds which come with the soil. "Pathogens"
might be a non-issue in outdoor pots of plants, but for indoor seed starting sterile potting soil and containers are generally recommended to avoid diseases like damping off.

As far as weed seeds, not an issue if you are an expert at ID-ing the seedlings you are trying to grow and can differentiate from the seeds that came along with the soil. But if you're trying to grow new-to-you seeds, it can be more challenging.


Burwash Weald, United Kingdom(Zone 9b)

Loon - I think this is a very interesting question, and it is the perfect time to experiment. I would grow at least two of everything, 1 in the woodland soil and one in purchased mix (just get a small bag to try it). If you are going to amend for drainage, I would suggest that you amend both of them the same (since you are looking at economy - how about some chipped dry branches instead of pearlite). I think I would try the two composts with some autumn sowing: try a couple of perennials that will like the early start, some sweetpeas which should be sown now, and some radish or winter lettuce. Try some indoors and some in a make shift cold fram (milk bottles with the tops cut off, sow in the base and replace top).

Do keep us informed - as someone else with woodland I certainly would like to follow your progress.

AuGres, MI(Zone 5b)

That is a great idea Laurie. I'll do it. I have a friend giving me some seeds today in fact. I have a ton of the milk jugs cut up. I had been using them to fill with water and drive the RTV around to water my container plants but when we got a late frost this past spring I cut them up to put over my plants in the vegetable garden.

I have lots of twigs I could chop up easy enough. I also have a lot of dried leaves I could chop up with them. I'll let you know.

Where does the bagged potting soil you buy in the store come from anyway? Don't they just dig it up from somewhere and bag it and sell it to us?

I live in a vey small town and I am trying very hard to not depend so much on buying so much stuff to garden with. We're looking to cut corners everywhere we can. I do love to garden though and I have all these natural resources around me so why not learn to use them. I know I could get pine needles from under the pine trees I have. Do you think that would be good to put in the soil I'm making?

Burwash Weald, United Kingdom(Zone 9b)

A lot of the compost these days come from the green material that use to go in dump sites. Most county councils run composting sites, they process in bulk and then sell on the finished product, or sell the collected green material to composters (it is often combined with excess paper and cardboard materials). It is also made up of the left over from timber mills and from forestry work. There is still a lot of peat extraction - but I have been warned off making comment on this. Most potting compost that you buy is soil free. If I am buying, I also look for peat free. No comment, just my preference.

Some of the very big commercial composters speed the process up by having steam forced through it - this keeps the moisture level at the right content and adds heat making sure the compost is sterilized, and killing off all of the seeds and pathogens. (Isn't the BBC a great institution, they did a whole programme on this!)

Pine needles make good 'leaf' mould that retains a slightly higher acidity than most leaf mould. They do need to be composted first, don't use them directly in your pots - they are resinous and take some time to break down. Chopping them and turning them helps. Well worth collecting up and leaving to compost in a pile.

AuGres, MI(Zone 5b)

OK, now you've lost me. I don't understand potting compost being soil free and peat free???? What is it made up of then? Maybe I don't know what the real definition of soil is. I don't know my "dirt" terms very well. Can you explain further?

I have a very large (50') pine tree next to my raised flower bed. It just naturally drops tons of needles onto the ground. I don't bother to remove them and they just decompose in there and haven't seemed to hurt the perennials growing in there. I do recall that pine needles make soil more acid. I guess I should plant a hydrangea over there by the pine tree. I bet it would do good.

I think I'll dig up my dirt out of the woods and put it into my two garden carts and shove it into the barn for the winter. In the spring my woods are very wet and stay wet for a long time. I don't want to try to use mud for my flowers.

My mother in law lived in Alabama on 100 acres on top of a mountain. She was one of the best gardeners I know. She's gone now for many years but I still think of her. She never bought dirt of any kind. She used to walk to the barn and dig up some aged cow manuer and mix it with the sandy topsoil around the fields and that is what she would scoop into her flower pots to grow her flowers in. She had the most beautiful flowers and she even had a little business selling cuttings through the mail. She would put in a huge vegetable garden and would can up 3 or 4 hundred jars of food each year. They lived on that food all year. She just made her own soil. I want to do that too.

Thanks for all the suggestions and help.

Burwash Weald, United Kingdom(Zone 9b)

First - I don't know if the terms are the same in the US as they are in the UK - so this applies to the UK: over here, potting compost/soil that you buy in the bags for sowing seed or making cutting is made up of a combination of things. Basically it is composted waste material the same as we make in our gardens, but it has been sterilized. Some producers add to that peat that has been dug from the peat bogs. There is no soil in a potting/cutting compost.

Many gardeners here are now refusing to buy blends that have peat in them. Its a conservation issue. And the potting /cutting blends sometimes replace the peat with composted pine bark or composted bracken to bring the acidity up to neutral/slight acidity.

I think your mother-in-law would be pleased with your ambitions.

Greensburg, PA

Loon, I am not an expert but willing to share what I do. First of all, most of my plants that grow outside are in containers, and I do agree with the earlier advice suggesting you read the Container Gardening forum sticky - you should find it very interesting.

Having said that, I move many outside container plants inside each winter, without problems with insects, disease, etc. Occasionally I may have to fight some aphids, but that pretty much the limit.

Here's my take on this:

Starting seeds indoors: If using forest soil for starting seeds, I would sterilize it. There are some different methods 1) Oven 2) microwave oven and 3) solarization. Make sure the mix you use is loose, check it's pH amend as necessary.

Growing plants outdoors or indoors in containers: See the Sticky mentioned. I would add the forest soil to my mulching bin, add some pine bark fines and some porous silica (something like OillDry - labeled for soil amending or kitty litter works for me). compost the mix (silica could be added later if you like) and use it for the plants.

Anything I have that gets transplanted gets its old soil added to the compost bin and new soil/compost from the finished bin. Thus, I am always recycling the old soil and building it for future use. I'm very pleased with the results and haven't had to purchase dirt for containers for a number of year now. You are very fortunate to have access to quality forest topsoil.

AuGres, MI(Zone 5b)

Thanks Krowten. I'll take your suggestions. I have a large compost pile. I need to build bins for it someday I guess. I do have two smaller Rubbermain compost bins but haven't gotten around to setting them up at this place. The only thing I put in my compost pile is leaves and grass clippings. That's it. Maybe I'll dump some dirt in there as well. I'll read the stickys in the container forum.

Greensburg, PA

Loon, I use a plastic garbage can to store my finished compost/dirt. Generally I will sift it through hardware cloth (1/2"). Big stuff goes back into the next bin. I try to keep the can mostly full, but there are times it is not. I use the can to also mix in the pine bark and silica, changing proportions as needed for what I am currently working on. Of course, it is also necessary to watch the mix and adjust amounts to match how much I will need. I am, however, careful with grass and only compost grass if I know it was not in seed. Adding soil to your compost before the pile heats will mean it does not get as hot. Also, because I sift it, it is important to make sure that it does not compact too much, thus the pine and silica.

I would really love to have access to forest soil like you have. It is a great, renewable resource.

AuGres, MI(Zone 5b)

Well, Krowten, maybe you can make a "soil run" to mid Michigan. :) I have 28 acres with 20 in forrest or woods. You can come dig up all you want to.

OK, I won't add dirt to my compost pile. My pile is huge. I'd say it's about twenty feet by 8 feet. We just dump leaves and grass in there. I never add grass when it's going to see in the spring. I've never added pine needles but I do have a big blue spruce tree that drops needles naturally into my flower bed out front. It hasn't seemed to hurt the flowers at all. I top dressed that bed this fall with crushed up dead ash leaves. I also put about a foot of leaves on top of the vegetable garden bed. By spring they are mostly decomposed and we just rototill them under. We tilled some under already and piled more on top. They seem to protect the soil for winter and there are always lots of earthworms in there in the spring. I have an asparagus patch in there that is bigger than I planned on. Who knew 114 plants would multiply so fast? Good thing we like asparagus.

Good idea to keep your finished soil in a garbage can. I have plenty of those. I don't add any food to my compost bin because living out here in the woods we have too many animals to content with that I don't want to attract. I used to sift my compost when I lived in the city. I made a giant sifter out of four boards and screen stapled to them in a square. I'd put it over my garden cart and shovel the compost out of the Rubbermaid containers and would knock the clumps with the shovel till they fell through. That just got to be too much work so I started just composting in place by adding a fine mulch of cocoa hulls each spring and lots of chopped leaves in the fall directly to the flower beds. I've gotten to be a lazy gardener in my old age. :)

Louisville, KY

I have used the following mix on my plants for winter storage. These are tropical plants that needed to be brought in for winter months and allowed to grow. I put them out every season and it is to expensive to buy new soil for this use.

2 wheel barrow loads of peat moss
1 wheel barrow of perlite
12 wheel barrow loads of very fine chopped up leaves or partially rotted leaves
6 wheel barrow loads of hard wood mulch.

This works well for larger plants that are not to picky. Some lime should be added to help make it neutral. I have sense been using a old leaf shredder that turns leaves into powder. It works well. The main thing is to make sure the soil is draining or holding enough water. As well as that it is not to acidic.

For me I mix up 15 bales of peat moss with 1 lb of lime and 5 to 8 bags of perlite depending on what it will be used for.

Sorry for the large scale mixes. I use a bob cat to blend the mixes together so I usually measure in wheel barrow loads.

Thumbnail by bwilliams
Bardstown, KY(Zone 6a)

Loon there is an article in this month's Mother Earth News about exactly your question.

Huh, dug?
Is there, like, a url?
Or do you have to be in North America and just buy hardcopy?

This message was edited Nov 27, 2008 10:52 PM

Bardstown, KY(Zone 6a)

I just happened to see the cover of the magazine yesterday. I just checked their site and found it.


Thanks !

AuGres, MI(Zone 5b)

Thanks so much. Interesting article. I've bookmarked it.

I do live in Michigan on property that is a wetland property. I had no idea that Michigan wetlands is where a lot of the commercially sold peat comes from. I've already got the huge leaf compost pile going. I have my pile on the edge of the woods.

Becoming potting soil self sufficient is my goal. I hope to never have to buy dirt again.

Thanks for passing along the informative link.

Norwich, United Kingdom

i probably shouldn't try to resurrect such and old topic, but i found it facilitating. and i have some experience doing this. Ive been on a budget for a while so paying 10-20 pounds on compost isn't really an option. There are woodland nearby and i usually get my potting tool and find a nice tree with lots of observable leaf mould and scrape of the top 2 inches then i use it straight away for my indoor plants, ive been doing it for a while.

The main drawbacks are, worms, they will eat soft flesh particularly Cati. So they can be a real issue. Another drawback is moss, which sounds crazy, but it has a tendency to grow from forest topsoil even in quite direct sunlight, but moss is quite good for soil as it works like a conditioner. however some gardeners might not want it for aesthetic reasons. The final issue and probably the biggest problem is using this potting soil in indirect light as it will grow mildew, no matter what you do. So treating a small amount and kept in storage is the solution.

Firstly separate the amount of soil you wish to use as treatment soil you wont need much for indoor use as only the top 2 or 3 inches should be sterilized, so about 3 litres should be enough

First of all soak the soil in vinegar until it is damp and smells vinegary dont use too much or you wont be able to dry it very easily and leave it for about 2 or 3 days leave it in a warm place to start drying it. spread it out thinly to dry it out in the sun or a warm window. once the soil is dry or dry-ish heat your oven to around 200c and layer the soil in baking trays in your oven. cook the soil for about 30 minutes. Some people use the microwave but i think that quite dangerous in case stones like flint explode breaking your microwave.

finally using small rocks to decorate between plants will prevent light from getting to the soil. so in your houseplants that don't get direct light make sure to use about 3 inches of treated forest soil, then decorate between the plant or plants with stones as this create a less hospitable environment for mildew to grow in. finally if you do see small specks of mildew growing in your soil despite everything we have tried then, mix a few drops of fairly liquid into a sprayer and spray the soil daily for a week even if it kills it straight away spray for the rest of the week, the mildew will come back but each time should take longer and longer to come back, repeat with a week long spray, eventually the mildew will stop coming back (washing up liquid is and old fashioned anti fungal)

because we only use a small amount of fairy in a large bottle (two small droplets per 1/2 litre) even very sensitive plants should be unaffected. soil in good direct light wont need treatment as fungus wont grow in direct light, so using soil straight from the woods is fine.

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