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re-use of growing mix

Posted by njitgrad NE NJ (My Page) on
Sat, Jun 22, 13 at 10:20

A couple of months ago I started a related thread in the vegetable forum but thought I would move it to here to get some more opinions.

Having never been serious about container gardening until this season (even more so with each passing day) I have a question that relates to re-use of growing mix.

I purchased large GeoPots this season in which I am growing tomatoes, peppers, eggplant, string beans and herbs. I used a 50/50 mix of garden-center organic compost to ProMix BX, nothing else. My tomatoes, herbs and beans are loving where they are. The jury is still out on the peppers and eggplant.

Looking ahead to the end of this season into the start of next season, I'm just trying to figure out ahead of time what I should do with the growing mix and the containers.

Before winter I want to wash and put away the GeoPots so I will have to dump the mix. I don't have any large barrels to store the mix, nor anyplace to store the barrels. My only option is to dump it all in a big pile in the middle of my garden on a tarp, covered by another tarp until Spring.

In the early Spring I plan to re-use the mix from the pile but only after mixing each shovel full from the pile with a shovel full of compost.

I'd like to know the pros/cons of doing it this way. From what I've read some people do something similar, others do not re-use potting mix. For the latter how does one discard it season after season if he/she doesn't have an area of property to dump it on.

Follow-Up Postings:

RE: re-use of growing mix

  • Posted by nil13 z21 Mt. Washington L (My Page) on
    Sat, Jun 22, 13 at 10:56

you would amazed at how much potting medium you can get rid of simply by spreading it in your perennial beds.

Count me as one that doesn't re-use organic media.

RE: re-use of growing mix

I reuse my potting medium, and I have some of these fabric containers as well as plastic containers. I don't see any reason to wash them and put them away separately, I just snip off the plants at ground level, leave the roots intact, and stack the things up against a garage wall. In the early spring I empty them out on a tarp or concrete slab, smack the root ball with a shovel, shake the potting mix out of the roots, toss the roots, and add what ever I need, mix it all up, refill the containers, and off we go.

There is a lot of very good information on the forum about proper drainage and aeration and why reusing potting soil can cause problems as the soil structure breaks down. Using cloth containers may well change the calculation because they act as a giant wick. I'm not qualified to pontificate, but with my own limited experiences with the cloth bags, the problem is keeping them wet enough. Versus hard-sided plastic containers where the problem is making sure there is enough aeration and drainage.

I sometimes store good sized quantities of dry potting mix in those contractor trash bags, or you can buy large plastic bins with a lid at any Walmart for <$20.

RE: re-use of growing mix

D makes some good points, and he uses a lot of common sense in his ideas. I have and have not re-used potting mix. Much of the decision is based on what I am planting. Some vegetables (like tomatoes) are prone to many soil-borne diseases. I would never re-pot with tomato soil to another tomato the following year. Your finances is a consideration as well. If you are smart about it (see above)...I think it is fine most of the time. Particles do break down smaller....however. You are only looking for a sanitary medium that drains...not one rich in nutrients. This comes with a complete fertilizer. Container growers feed!

RE: re-use of growing mix

Hello all,

I use many, many earthtainer, earthbox and 18-20 gallon containers for growing. These containers keep their potting medium with only a refresh each spring. I occasionally toss the potting medium when we need to top off our raised beds. DH removes about 25% off the top of each container each spring and mixes in new Dolomite and new potting medium to fill the containers before planting. Our plants do seem to prosper.

Occasionally I notice that an earthbox or earthtainer is compacted and not wicking correctly and then I completely replace the potting medium but the old mix is incorporated into the raised beds.


RE: re-use of growing mix

In my experience a pine bark based potting mix lasts a good three years. It's way too much work to replace mixes in all containers every year. On the big containers each Spring I take a handful in various spots to feel if its still "fluffy." If so, I defer a year. Tomato containers get remixed every other year with 50% new pine bark / 50% recycled mix. This year I decommissioned a 25 cu. ft. container with mix not changed since Spring 2009 (seems like yesterday!). That mix was broken down and not fluffy. It's hard to describe how fluffy feels. I squeeze a handful of mix and then open my hand. If it sticks together, balling up like a dirt ball, it's not fluffy. After doing this awhile you'll acquire a feel to it.

RE: re-use of growing mix

The problem with your plan is that both the promix and compost are made of fine particles that will breakdown and get compacted in the first season. I would mix it with an equal measure of pine bark fines to rejuvenate it for the second year. I use the 5-1-1 bark based mix that many on this forum favor. I keep about one-third of it and mix that with new 5-1-1 each season, except I do use fresh mix for my tomatoes for the reasons noted above.

RE: re-use of growing mix


I keep hearing about pine bark fines. Can someone describe what this is to me? Perhaps a photo of a bag of it? The people that operate the nurseries local to me are clueless so if I ask them all they will tell me is that yeah we carry several different type of pine bark.

If you only keep a 1/3 of your previous year's mix, what do you do with the remainder? I don't live on a property with woods or anything like that so I couldn't just dump it in the back of my property.

RE: re-use of growing mix

Usually called Pine Bark Mulch, or Soil Conditioner. Sold at big box, garden centers, nurseries, etc.. Sometimes can be bought in bulk from mulch suppliers. Comes in various degrees of decompositon from uncomposted to heavily composted. Here's a photo of uncomposted Agway stuff.

RE: re-use of growing mix

I'm a bit confused here.....please bear with me.

In a thread that I posted in search of a ground cover for my raised beds, several people have warned me about using wood chips around my plants because it would tie up the nitrogen in the soil.

How does using pine bark mulch in such a large ratio not lead to the same problem?

RE: re-use of growing mix

Wood chip mulch is made up of sapwood and hardwood, not pine bark. It is often made from old wood pallets, and will cause many problems in soil, including nitrogen draw down. According to Al (tapla), the forum member who developed the 5-1-1 and gritty mix so many of us use:

"The reason conifer bark works so well is that it contains more lignin and MUCH more suberin (natures water-proofing for plants), which slows breakdown of the hydrocarbon chains (that the bark is made of) by microorganisms. Any hardwood or sapwood chips will break down quickly, leading to structural collapse of the soil and a very high degree of nitrogen draw-down (unavailability)."

If you haven't read the Container Soils thread that's been running on this forum since 2005, I highly recommend it.

Here is a link that might be useful: Container soils -- Water movement and retention

RE: re-use of growing mix

Thanks for the clarification. I may just give the 5-1-1 a shot next year however I have to say that my tomato plants thus far have been the largest I have ever grown and I'm not sure I want to deviate. Perhaps its my soil mix or the new fabric pots, or both, I am just amazed at how tall my plants are and its not even July yet. By far my best season yet.

I still want to find out what you do with soil mix that you won't be reusing. You said you only reuse 1/3 of it. Do you put the remainder to some good practical use? Can it be spread on a lawn to fix bare spots in the Fall/Spring? Would it be good to use in raised beds?

Thanks for the pic, now I know what to look for.

I like your approach. I'm the type of person that prefers to have a system year in and year out so I may adopt something like what you do.

How often does one need to fertilize after transplanting in a 5-1-1 mix? I watched the video where Osmocote Plus was mixed in when the 5-1-1 mix was made. How long does that last typically?

RE: re-use of growing mix

I started using 5-1-1 for my vegetables and flowering annuals in 2011, so this is my third year. I have been so happy with the results, that I am growing more container plants each year. For example, i grew four tomato plants in 25-gallon smart pots in 2011. Last year i grew seven, and this year i am growing 10. So part of the answer is that I use some of the old mix to make up the mix for the new pots. I also grow about a dozen hanging baskets of flowering annuals each year. At the end of the season I dump them and the soil they grew in into my compost bin.

At the end of the vegetable growing season, I remove the plants and their rootballs from my containers and add them to the compost pile unless the plants have shown any diseases. I make an exception for tomato plants, which i dispose of completely so as not to risk carrying over soilborne diseases. I remove the top 5-6 inches of mix from each vegetable pot and use it like a mulch under shrubs at the edges of our yard. The last couple years I decided to leave the rest of the spent mix in the smart pots with a layer of shredded leaves on top.

When spring arrives, the mix has reduced to fill about two thirds of each pot. I remove about half of the mix from each pot and use it as an addition of about 2 extra parts to the fresh 5-1-1 I make for new plants. Then I mix controlled release fertilizer and gypsum (for calcium) into the old 5-1-1 in the pots. I top each pot off with fresh 5-1-1-2.

I have used the spent soil left over after all this to "hill" potatoes in large containers and to create a few small raised bed garden plots in my yard for things like garlic, herbs and flower bulbs. I grow almost everything in containers because my small yard is surrounded by black walnut trees that poison the soil for most of the things I want to grow. If I could add the used 5-1-1 to a raised bed, I would.

What I do may not be ideal, but it saves me a little money and effort and it satisfies my Scottish sensibilities.

RE: How often to fertilize when using osmocote

I use osmocote plus CRF in my 5-1-1 at the rate of 1 tablespoon per gallon. That amount will not be enough to feed any of the veggies and flowers I grow outside adequately over the summer. I usually start feeding them with a complete soluble fertilizer used full strength after about a month. The CRF is only a form of insurance. It is especially helpful when we have a lot of rain at the beginning of the season, which prevents me from watering. Container vegetables need regular feeding to thrive. The compost you use probably doesn't provide enough food for your veggies without a little help from fertilizers.

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