adding compost to container gardening soil mixture?

kawaiineko_gardener(5a)March 15, 2011

First off (this is preemptive) I've tried looking up threads using the search option about whether or not you can add compost to your soil mixture for container gardening. I didn't really find anything that answered my question which is 'can you add compost to container gardening soils or not'.

I know that with container gardening you basically have to use a soilless mixture for your soil. If the soil mixture is too heavy, it will wreck havoc on your plants.

It works wonders but my question is about fertilizing namely. I was told even if you use commercial fertilizer, but you don't amend your soil mixture with compost, you'll have problems with soil fertility. My question is the recipe doesn't specify to add compost to the soil mixture.

My concern is that if I add the compost it will make the soil mixture too heavy? I've found something called 'compost tea' which is essentially microbes for soil. Would this suffice as compost for container gardening?

Will adding compost in addition to a commercial fertilizer be over fertilizing? I'm only going to add compost if it's something that's necessary.

If so, how much would I need to add for the big batch of container gardening soil mixture listed below? Would I just measure it out and mix in along with the other ingredients when I first make my soil mixture, or is it something that would have to be applied at intervals?

The basic recipe I use for container gardening is listed below:

5 parts pine bark fines (partially composted fines are best)

1 part sphagnum peat (not reed or sedge peat please)

1-2 parts perlite

garden lime (or gypsum in some cases)

controlled release fertilizer (if preferred)

micro-nutrient powder, other continued source of micro-nutrients, or fertilizer with all nutrients - including minors

Big batch:

2-3 cu ft pine bark fines

5 gallons peat

5 gallons perlite

2 cups dolomitic (garden) lime (or gypsum in some cases)

2 cups CRF (if preferred)

1/2 cup micro-nutrient powder (or other source of the minors - provided in some fertilizers)

Small batch:

3 gallons pine bark

1/2 gallon peat

1/2 gallon perlite

4 tbsp lime (or gypsum in some cases)

1/4 cup CRF (if preferred)

micro-nutrient powder (or other source of the minors)

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I'm sure Al can explain it all much better than I... but based upon what I know, I leave the organic gardening methods and ideas for the gardens... and I stick with a more inorganic approach to container growing.

There are vast differences between growing in the ground and growing in the confined space of containers. It's next to impossible to maintain the same balanced ecosystem we find in the garden, in a container environment.

I wouldn't use any compost, worm tea, fish emulsion, or anything else of an organic nature for pot culture. It's so much easier to control everything when you know the exact nutrients, ratios, and percentages you're feeding your plants. A liquid chemical plant food gives me that control.

In the garden, I'm all about organic... because I have the help of Mother Nature and her vast army of living things all working together to decompose matter into usable food, and to help maintain the balance of good and bad things, like bacterias and such. I don't have to worry about imbalance or exact percentages. This same ecosystem isn't present within containers.

My advice is... save the compost for the garden. Pot culture is vastly different.

    Bookmark   March 15, 2011 at 6:33PM
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jwahlton(9B Kisimee)

I have to say that last year I did compost, peat and perlite. Don't remember the amounts, just mixed it on a tarp until it looked good to me. I had amazing results with my tomatoes in containers. I know that people say not to use it, but it worked for me

    Bookmark   March 15, 2011 at 8:28PM
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Hi Jwahlton:

You said:" I know that people say not to use it"

I would say that the majority of the ones I know here are saying it is 'healthier' from a plants perspective to grow in a fast draining mix and with good fertilizer that is readily available and guaranteed success.
It is more reliable, and the science behind the workings in a container are fully explained for those who want to know why their plants fail using your method, as mine did, and not just grow by luck.

Like you said, you don't remember the amounts you used, and it looked good?
So therefore just by a draw of the straw, you happened upon a good growing season. Congrats!
Most are not that fortunate, so therefore many choose to grow the way that is 'reliable' and works every time for their plants. I too get tons of tomatoes guaranteed every year now, and not just a couple here in there growing in dirt and compost by just eyeing out my mix.

Congrats though on your success and I hope it works out for you just as last year.


    Bookmark   March 15, 2011 at 9:07PM
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jwahlton(9B Kisimee)


I said what I did last year, when I was still learning. I've done a lot of reading and research now and will be using the 5-1-1 in my tomatoes in containers. I do understand the concept. Yes I had luck last year, but want even better luck this year so will go with the tried and true. Although my luck didn't hold out when I fell and broke my wrist in 3 places while ammending my soil in the garden! It's difficult to garden with a huge cast on your arm, but I did my best.

    Bookmark   March 16, 2011 at 1:59PM
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FWIW, I use something similar to what you use and have good results. I have mixed compost with bark and perlite, but, for convenience, I generally use bagged soil, perlite/bark with good results. Both methods work without problems.

When something works consistently, I don't think of it as being lucky. It works.


    Bookmark   March 17, 2011 at 7:46PM
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Scientific evidence supports the idea that, due to the huge differences in pot/ground culture, it's best to save compost for the garden. But if the OP begins with, "I know people say not to use it..." then doubt is already present and all that's needed is the explanation, which has been given... more than once, if memory and search tools serve correctly, and I believe they do.

    Bookmark   March 18, 2011 at 8:17AM
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tapla (mid-MI z5b-6a)

I think it's a good idea to keep in mind two things. One is there are ways to combine three perfectly good ingredients and end up with a whole that doesn't reflect the suitability of the individual ingredients. An example is you might have gastric penchants for ice cream, taco salad and beer, but it's a good bet that combined in the same bowl, the product may not be as palatable as the additives are individually.

The second thing is that when using the adverb "well" to describe how something works, we are only using the 'positive' degree (of comparison). When something works well, it still leaves better and best as the other two degrees, the 'comparative' degree and the 'superlative' degree.

My observations lead me to the conclusion that you can indeed combine pine bark, compost/peat/peat-based bagged soils and perlite to make soils that range from practically unusable to superlative. I've been helping people combine soil ingredients for a while now, some of them based on these very ingredients. Still, there is no getting around the idea that soils covering ALL degrees of comparison, all the way from (nearly) worst to (nearly) best are possible with the same ingredients. How these ingredients are combined, and attention to details like particle size are, in the end, what determines where these soils are situated among the various degrees of comparison.

If you compare a soil that works 'well', to a soil that is the 'worst', the best we can say is it works 'better than the worst'. If we compare it against the soil that works the 'best', we can say it works poorly in comparison, or it works worse than soils that are either 'better' or 'best'.

Just a little bit of musing to help put things in perspective. I've never been happy with the positive degree of comparison ('well'). I've always tried for 'better, closing in on best'.


    Bookmark   March 18, 2011 at 10:49AM
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Nothing in life is perfect. Wouldn't it be wonderful to have the best soil, light, rain, weather, time and money?

Unless you grow in a lab with controls, perfection is an individual experience. My concept of 'best' is what satisfies me. There is always the thought that things could be 'better' but a person could drive themself crazy never being satisfied with anything they do.

Best, better, well, good, great, perfect...if one is happy with their results, they all work.


    Bookmark   March 19, 2011 at 9:22PM
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tapla (mid-MI z5b-6a)

Indeed, it would be wonderful to have the best soil, light, rain, weather, time and money, which is why so many of us are willing to work hard toward those goals over which we DO hold sway. I do think that striving for perfection can be demoralizing, especially for certain people, but striving for excellence is motivating because excellence is achievable; it acts like the carrot dangling in front of the tortoise. Just the striving for excellence, let alone achieving it, benefits both the self and others we touch ..... and how else would we put our talents to work if we didn't strive for improvement? No one talented ever strives for mediocrity? Given the choice, would we surround ourselves with the complacent, or people embarked on the path of self-improvement? Even though it's true that nothing is perfect - better a diamond with a flaw than a pebble without.

In the end, we each and all have to decide for ourselves what we're happy with. Being exposed to new knowledge is often unsettling to those who are willing to work to improve. They get a taste of that knowledge and want more - want to implement what they've learned. That's what all the enthusiasm is about - hard workers striving for excellence, and I applaud all that are here & willing.


    Bookmark   March 19, 2011 at 11:07PM
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Al, I've appreciated the thoughtfulness and vigor with which you approach your subject and have learned a lot from you while browsing these forums. I have around 300 plants in containers, in and outdoors, orchids, ferns, common junk stuff, lots of epiphytes on wood, begonias, vegetables, maples, succulents, cacti, etc. I haven't given them a lick of inorganic fertilizer in three years and would agree that the results can be mixed. Lately I've been brewing my own actively aerated compost tea using homemade worm compost, kelp emulsion, a handful of good garden soil, and a few other organic additives in small amounts. This mixture is aerated and vortexed for 18-24hrs during which time the microbial populations multiply, making a rich actively biological soup. I use this regularly on all my plants, and fertilize between compost tea applications with organic seaweed or fish emulsion type fertilizers. I also keep a small anaerobic compost tea brewing and I'll use small amounts of this every month or so. Since I've started using the compost tea my plants have all seen a remarkable uptick in both foliar growth, blooming, and just general "health" as compared to just organic fertilizers. My take on it is that the compost tea supplies a steady stream of microbes that the plants can symbiotically partner with to convert the organics into usable nutrients.

I totally agree that good drainage is key and if the soil is too heavy the compost tea can quickly turn anaerobic in the pot and result in all sorts of problems. A fast draining mix combined with regular compost tea applications and organic fertilizers seem to have a lot of advantages and to keep my plants reasonably healthy.

I can't tell you exactly what proportion of NPK the plants are getting, instead I rely on an entire ecosytem with all of its sloppy redundancies to allow the plants to orchestrate their ancient microbial dance and get what they need.

I understand that chemical fertilizers work, it's just the widespread and longterm impacts that these substances have on the larger ecosystem (gulf dead zone, algal blooms, groundwater nitrification, etc) that makes me want to avoid them, even for container culture. Nurseries are large contributors in this nutrient-pollution overload, but if you add up all small-scale homegrowers who put miracle-gro on their tomatoes it equals a whole lot of nutrients that are being converted from fossil fuels and released into our larger environment. Historically nitrogen has been a severely limited nutrient on the earth, thus the biosphere's incredibly tight hold on it via the humus and soil building processes.

I totally respect that you seem to be solely interested in what's best for the plant when it comes to container culture, and I agree that inorganic fertilizer do yield amazing results. But I believe we need to think beyond the individual plant, to the ecosystem in the pot, and then to our wider community or plants animals and humans that we share our planet with. We can (we have the choice!) develop new technologies and techniques that allow us to avoid the use of chemical fertilizers that imbalance our environment and tax our natural resources and instead rely on the built-in recycling and life-support systems of the greatest systems engineer imaginable, mother nature.

    Bookmark   June 25, 2011 at 2:21AM
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What was the original question ? Oh Yeah ! Riveting discussion ! Substrate for containers can be many things . Some limiting factors to keep in mind though , are texture, porosity, nutrient/CEC levels, and water holding ability . Know what you put in ( do your research), and put in what is needed . Compost, if used in SMALL proportions (10-20%), can be beneficial to all of the above factors . You can still use whatever you want (organics, synthetics, or SRF) to maintain fertility .

    Bookmark   February 26, 2012 at 1:51PM
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