Your soil's pH tends to rise as the soil ages. The Mg fraction of the dolomite is much more soluble than the Ca fraction (about 125X), so you probably don't need additional dolomite, but you will need to replace the lost Mg fraction. I would do that by adding 1/4 tsp of Epsom salts to your irrigation water every week or two.

Bone meal breaks down so slowly in containers that you should consider it insoluble (and ineffectual), so it won't need to be supplemented. It looks like the kelp meal and blood meal are the only amendments that would need replacing.

I don't reuse soils because the continual breakdown into smaller particles clogs macro-pores and makes for a very water retentive soil. If you must reuse it, you might wish to consider mixing your old soil into several parts of pine bark fines and some perlite to stabilize its structure and provided needed aeration.

Al

Yeh Al Just about what I was gonna say except I didn't know half the stuff you do about container mixes:) I do reuse a lot of container mixes for outdoor plants but mine are very course to start with and contain little in the way of fines. Most of mine are pumice based, which I have had good luck with but I lost my local source for pumice that was reasonably priced. When old Dave Grigsby was still alive at Grigsby's cactus he sold a pretty big bag for a couple of dollars. I had some on hand for a long time but I must look for another source. It doesnt contain any nutrients that I know of but it retains some moisture and seems to drain perfectly, if that makes sense? I always like to read your posts Al. steve

Al said "I don't reuse soils because the continual breakdown into smaller particles clogs macro-pores and makes for a very water retentive soil."

I don't get it....

Whats the difference between a pot
and a raised bed (a larger pot)
We don't discard raised bed soil why would we discard pot soil.

My garden is currently an all container organic garden. By that I mean it is in pots of all sizes (small to 15 gallon). I'm also in the process of re-conditioning my soil. I agree with some of the previous posts in that in addition to adding nutrients you need to improve or re-invigorate the structure. The aeration needs to be improved.
I will actually dump out the old soil and mix it with my compost mix. This is a good time to blend in the other ammendments if wanted.

Al, you have the pH info backwards. A soil's pH will tend to lower, or get acidic,as it ages. Mg is not often deficient in soils, especially if one is using good compost and/or bone meal, so maybe not a concern.

There's a significant difference between a container and a raised bed. One is the relative size and the volume of soil. But of far greater importance is the drainage aspect. A container relies on a couple of small holes to which ALL drainage is limited and except for these holes, the bottom is enclosed. There is no such enclosure with a raised bed - the entire bottom is open and available for free drainage. That is one of the primary reasons why garden soil can be used freely in a raised bed but should be avoided in a container growing situation. Because of that characteristic - a wide open base for drainage - there are fewer/no concerns about perched water tables with raised beds so if the soil particles degrade (and if composed of a high proportion of organic matter they will) and become more uniform in size and with a consequential reduction in pore space, drainage will not be compromised to the same degree it would be in a container.

Al would explain it much better than I and hopefully he will chime in to clarify what I have bungled :-)

DBM - check your information. While you can halt or reverse the normal upward creep in aging media pH with a program that includes acidic irrigation water and acid forming fertilizers, the norm is to see container media rise in pH as it ages. We see this born out very frequently when we see micro-nutrient deficiencies developing in aging media even though we maintain the same fertilizer regimen that includes the deficient elements, often Fe and/or Mn. We usually need only to acidify the pH of our irrigation water to neutralize alkalinity as a corrective measure because the nutrients are present, but unavailable (locked in insoluble compounds) due to high pH.

Also, container soils are generally deficient in Mg (and Ca) unless supplemented - usually with dolomitic lime or MgSO4/Epsom salts - if using CaSO4/gypsum as a Ca source. Additionally, most commonly used soluble fertilizers contain no Ca or Mg (ck the MG, Peters, etc., label), which increases the potential for a Mg deficiency.

Jon - the difference between a pot and a raised bed lies in how water behaves in the distinctly different cultures. On a scale of 1-10, with 1 being growing in raised beds and gardens, and 10 being hydroponic growing, growing in a container is around a 7 or 8. IOW, it has MUCH more in common with hydroponics than it does with gardening in soil. Much of what works very well in the garden, is useless or harmful in container culture. The PRIMARY difference is that the earth acts as a giant wick in a raised bed, and virtually eliminates the problem of perched water, which needs to be carefully guarded against in container culture if your hope is that plants will grow at as near to their genetic potential as possible.

Also, while the whole "feed the soil so it can feed the plant" thing, which I adhere to rather strictly in the gardens/beds, can be thrown right out the window, as long as you're not chained to a particular ideology; and, you can have perfectly healthy plants, with less effort and with a greater margin of error than you can if you've self-limited your options.

Al

First, thanks to all for info!

I thought the vermiculite helped aerate the soil and thought it would continue to aerate - even as the compost and peat broke down. Maybe that assumption is incorrect? Is that why I should add perlite - or more vermiculite?

Was also thinking I might add more compost to the mix, but then worry about making the mix too dense (which is why I started last year by combining compost with equal parts peat and vermiculite) - and not knowing how to make sure soil is sufficiently nutrient rich.

My biggest problem is being a novice gardener. I know enough to spot the issues and ask the questions, but have no idea how to answer them!

Vermiculite starts to break down in container media in about - ohh ....... say 10 minutes. ;o) It's only real value in most cases is ADDED water retention, which is certainly not needed (from the perspective of the plant's preference) in peat or compost-based soils. Perlite is a better choice.

May I suggest you try to get a better understanding of how water behaves in containers and maybe some additional information I hope you'll find helpful at the link I left below?

Here is a link that might be useful: More about container soils if you click me.

OK,
I need your help.
You guys are killin' me ;-)
I didn't know better ,so I "apparently", did the wrong thing 2 years ago....
I was having Ground Squirrel/Moles (some little beasties) anyway.... were harvesting my Garden Veggies before I got the chance to partake.

So I decided to pour a solid concrete slab and utilize concrete cinder blocks (2' tall walls/3 blocks high) to create raised beds that were impervious to the little monsters.
I realize I could have and Y'all probably think I SHOULD have, instead installed woven screen instead of concrete as the Base to keep out the critters, but alas I did not.

My raised bed garden has for the last 2 years (10'x30') provided over 600 lbs of Food for the Josephine County Food Bank. My Tomatoes and my Lemon Cucumbers are over 10' Tall.I prune them at 10' because I don't want to go higher on my ladder to harvest them. Everything that I plant in this "container" grows like there is no tomorrow.

I have actually heard many times derivatives of the remark "I have seen lush gardens before....but nothing this lush "

Now...Even with that success...
I am now wondering (because of what I am hearing you saying) if my garden is on ...(borrowed time).....

Is what I am hearing you say,that my garden (despite the size) is really a... pot...and as such has a very limited life span of usefulness, and will have to be emptied as opposed to replenished on a regular basis.....OUCH ;-(

It does drain well (though I am sure ,not as well as could be achieved on native soil) whenever the soaker hose system is running, it drains from the block (between some mortar joints and such)....

Oh ...this is not good news ...

Al,I apologize if I'm not understanding you correctly, but I'm not following your soil pH dynamics. Is this specific to your soil mix? Container style? The general trend for soils that I learned is that the hydroxides (-OH groups)are soluble, not held strongly, and will leach out over time. Assuming you don't have hard water how does a soil increase in pH?

curious,David

OK...Here goes:
I know you all read these posts as soon as they come up, so by not responding yet ,I am going to leap to some conclusions, based on that presupposition.
Y'all are just trying to be nice and not "jump all over the new guy", but I have real consequences if my gardens don't produce to their potential... I don't want my ignorance to be the factor in some people not being able to eat fresh vegetables this coming season.
I will remove the soil from my raised beds, jackhammer out the concrete from the interior section (to create the more natural wicking effect of the earth ),and install tight woven mesh at the base to keep out the monsters.

The reason I need to know this information now is because I am slated to pour concrete today for my new raised beds.
I already have them formed and was ready to pour concrete yesterday but it rained, so providentially I happened upon this site, apparently just in time.

With the new beds ( 900 square feet )and based on my past gardening successes ,I was going to increase from 600 lbs of food donated to the local food bank to over 2000 lbs.

So before I pour ,I just want to be sure, the way I did it before, is NOT as good as can be achieved , if I leave the bottom opened up the the earth,....right ???

'Morning Jon, I wouldn't read too much into the lack of responses, people might be busy, or they could be worried about another 're-load', or, or ,or....

I have zero knowledge about container gardening or gardening on top of concrete. I wouldn't do it myself because it just doesn't seem right to me, but that's entirely a gut feeling.

I think if you intend to jackhammer out the first one, why would you pour the second one?

Lloyd

So before I pour ,I just want to be sure, the way I did it before, is NOT as good as can be achieved , if I leave the bottom opened up the the earth,....right ???

Short answer....yes :-) Personally, I believe the one of the major benefits of raised beds is lost if you provide an impermeable base.

Ok jonhughs just let me say I am responding not because of my vast knowledge but I wouldn't pour a slab and then form a bed on top of it. I think that could cause problems. As you said before, maybe us hail screen in the bottom to keep out the critters. then build your beds around the screen. But hey I would use the beds you already have as long as they work for you. Then if they start to cause problems to the growing plants, tear up the bottoms and start from there. You may have the best system going for your situation right now. Remember, we are all learning here, not just you. have a great day steve

Hi Lloyd, Initially(before yesterday) I was simply going to pour the slab and build the walls, ...

Now ... I am going to pour FOOTINGS only and then build my walls.... I will use 1/2" x 1" welded wire on the base to keep out the critters...

Steve, Because my existing raised bed floor was poured inside a previously built exterior perimeter wall, it has drainage at that connection as well as drainage through the blocks and mortar in the interior walls, and because it grows vegetables like it has been blessed by God, I will leave it for now and see how it performs ,,, especially now that I will be able to see how each performs ...side by side... if you will ;-)

VAL ... As you said, there are lots of good reasons to keep the earth accessible to the raised beds, I really just don't trust ANY fabric (Galvanized steel or not) to last ... and because I didn't want to have to re-do it ....again and again ... I went with concrete.... OY VEY

That came back to bite me in the butt ;-)

So ...as it stands, I am pouring the footings today and will commence the building of the walls ....soon... ;-)

Thank You ALL so much... God Bless You and Yours ;-)

In the possibly immeasurably more mundane world of my small container garden, ;) , I am wondering what, if anything, I can use the potting mix from my containers for. Does last year's mix have any soil integrity left that makes it a good, or bad, idea to dump it into my flower beds? Or should I just throw it in the garbage? Please help! I really don't know what to do with it.

Use it as mulch on your beds or garden - turn it into the compost pile - if you feel you need to reuse it, mix a small fraction into a goodly amount of pine bark fines, add a little perlite and some garden lime & you'll have a durable and productive soil.

Al

I'd still like to understand "the normal upward creep in aging media pH "and insight into "the norm is to see container media rise in pH as it ages"(Al).
I entered this forum to learn new stuff and this idea of a naturally rising pH , wich is the reverse of what I would assume, is very interesting. My education is of field soils , so the idea that a container media has different dynamics is believable and exciting.

You already corrected me in two areas, so I suggested you check your source. It's off topic, but I'll briefly expand.

First, pick up any text on managing container crops (greenhouse/nursery) and you can read about the strategies employed to manage media pH. Basically, you'll find that because container media has low bulk density/buffering capacity, that irrigation water (alkalinity) is the driving force behind pH fluctuation in container media. Since virtually all municipal water supplied is alkaline, and the hobby growers I'm addressing generally don't have the knowledge or equipment to manage their high alkalinity water, the tendency is for media pH to rise.

What happens is during the dissolution of limestone added as a Ca/Mg source and to adjust pH, some of the CO3 from the limestone neutralizes the H+ contained in the soil solution > carbon dioxide and water. As the H+ is reduced in the soil solution, additional H+ moves from the exchange sites to the soil solution and is neutralized by the lime. Then, Ca/Mg2 from the neutralized lime moves from the soil solution to media exchange sites. Net, is that the exchange sites become saturated with mostly calcium and magnesium, and the concentration of H+ in the soil solution is reduced (thanks in a major way to the compounding effect of the alkalinity of irrigation water) > higher media pH.

Al

So it's an individual water issue. thanks

Talpa: very nicely explained. Wish I remembered everything from my college courses in ornamental horticulture.

Michael

To johnhughes, it does seem odd/unnecessary to have a raised bed with a concrete bottom, but if it's been kicking butt for two years in a row, it's not broke, don't fix it.

To greenesmith, on the reuse of potting mix, I do it all the time by sifting and blending in fresh sifted compost. However, the buildup of alkaline salts is a real thing. Fortunately my wife is not so frugal and buys bags of potting mix which goes into the blend, so it doesn't seem to get too crusty with lime. My biggest problem is disease - I think I've got rampant wilts in my garden, compost and potting mix, to the point I'm ready to try the nuclear option. So watch the reuse of potentially diseased stuff.

Perhaps the 'disease' diagnosis is inaccurate and the sifted soil/compost and its inherent water retention the culprit. The building of soluble salts should be a non-issue in free-draining (container) soils that can be watered to saturation and beyond w/no concern for root rot. Soluble salts build-up should also be a non-issue in raised beds for the same reason.

Al