Here's a photo of a cross section in this area. I'll post another photo in a separate place. All of the contractors we've had in this area remarked on the cruddiness of the soil, even for Middle Georgia. One contractor was using a trencher to lay electrical lines, and the hard-pan clay broke the teeth off the trencher.

One more photo.

With the location's history I am inclined to say you may as well till it up a bit and have a soil test done to see what oddities being used as a parking lot caused then treat accordingly.

Don't go nuts. Just try to get the area back to normal.

Neat project btw.

Is the soil native or is it fill from the former parking lot?

What is the contour like? Is there standing water during hard rains?

What is soil drainage like? The picture does look pretty bad, but sometimes it's hard to tell from a picture.
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It sounds like you are thinking this through pretty well. I have seen people recommending amending larger areas, as you describe, thinking that that will make everything OK. But, just as you mentioned, a large "bathtub" is still a "bathtub". Amendment is often bad for more reasons than one. Drainage is probably the main issue, and that's the one that won't get fixed by increasing the area amended (assuming reasonably flat ground). Unless you can change the soil profile all the way down to a better draining level, (heavily) amending the soil may only increase the problem. Another issue is soil interfaces causing poor root formation, and that problem can be addressed by amending a larger area.

Depending on the specifics of the situation, berms (especially larger-area berms) may be of great help. If created carefully, they can look very natural.

Heavily amending an area is what really can cause problems. Adding only 10% compost, soil conditioner, or whatever is much less likely to cause a problem. The time scale for this project may also make a difference. You could do a lot more for the soil if you have time to do it. Berms may be a quicker way to improve drainage.

Exactly. I was already thinking that the drainage was the more important issue, and after reading one of your four-year-old threads (a great, fascinating debate with harvestman), my thinking about drainage was reenforced. I'm working with a terrific city engineer who is going to grade the area so it drains properly, but he doesn't want to use storm drains, so it's all through natural shedding, which will take some tweaking. Right now, we haven't finished grading, the sod hasn't been brought in, and there are places of pooling water. But mainly, the soil is just saturated and doesn't seem to dry after rains, but in a drought, it's hard as rock. We built a couple of rain gardens in another section nearby, and one drains in a few hours, while the other, just fifteen feet above, drains in three days. We found out it's sitting on a shelf of hard-pan clay, and that's what the situation is here.

From what I can tell, the city restored the park once before in 1914, and when they did, they chopped down every tree (in an attempt to bring the capital of Georgia to Macon), and they manured and harrowed the grounds. But that was the last time the park was amended. Before that, the park had mainly pine trees and mangy grass. So I'm assuming it's native clay underneath. Since then, this section of the park has seen very few trees, no humus built up from leaves, etc., and lots of cars driving everywhere. When the parking lot was removed, a whole lot of slightly better dirt was dumped in order to grade the dip where the parking lot had been. The Project Manager/city engineer wants to till the soil, bring in about 2" of decent sandy topsoil for the top in order to root the sod, and then he wants to rip the clay wide, break it up, and back fill again with the native clay. That seems to be your advice for the trees too, but I wonder if amending with 10% might not give the trees a better shot, provided that 10% is well turned over a 30 foot wide area. I worry less about the blackgums in this situation than the Princeton elms, which I've seen struggle in some of Macon's plantings.

An arborist down here was thinking about keeping the planting hole native, and then, to encourage root growth, amending the wider root zone around the planting hole--sort of reverse psychology for tree roots. I've not seen this advised anywhere, though.

I'm hoping to create a slight berm for the elms and other trees, and I'm hoping to plant those elms 3 inches above grade. But they'll still be in the sucking mud after rains like we've had lately. And that mud will remain for 4-5 days. So it may not have standing water, but it'll be soggy.

The park in 1889 before it was harrowed. Drainage has been an issue since the 19th century. We're planting in the left lower corner, which seems to be covered in water here too, doesn't it?

Here's the only other photo I've found of the park before the soil amendments came in 1914. Tennis in 1889. This is fairly close to the planting area too. Maybe I should have planted pines instead of elms. In fact, the Virginia pine might be the only tree that looks happy out there right now. The willow and pin oaks which were planted in 1993 look like they're ten years old instead of twenty, and their roots all look stressed. One thing we need to do is keep the area well mulched at all times.

What I'm mainly thinking is that I should have gone with my first choice--the swamp white oak--instead of the American Princeton elms for the allee of 18 trees coming up this path.

Brandon7, when I read that earlier thread about amendments, I thought your logic persuasive, but I also thought back to this piece about the Washington Mall's restoration of the area they planted their American elms. What do you think of this advice?

"While elms are tolerant of adverse conditions, like any tree, they would thrive under better soil conditions. Compaction is not naturally alleviated even over the long term. Once soil is compacted only deliberate management tactics can alleviate the problem. In areas where turf is the only vegetation, soil can be renovated. When trees are present, however, options for soil renovation are limited. Tree roots in compacted soils are close to the surface and extend widely. Expansive deep soil renovation by tilling can destroy much of the treesâ root systems. Soils around trees can be surface drilled to improve aeration and top dressed with organic matter and inorganic, light-weight aggregates that resist compaction. Routine top dressing helps renovate the surface soils and alleviate hydrophobic surface crusting and compaction, thereby promoting moisture penetration and gas exchange. While these measures are helpful, they will do little to alleviate extensive deep compaction. The best opportunity to remediate soil compaction is when trees are planted. Soils can be renovated over an expanded area, 20-25 feet, beyond the planting pit. Existing soil should be tilled to a depth of 18 inches and mixed with organic matter and Soliteî or other inorganic material that will enhance and retain pore space while resisting compaction.

When multiple adjacent trees are being replaced an even greater area can be renovated. Expansive and extensive soil renovation will enable tree replacements to quickly fill canopy voids and sustain long term growth. Recognizing the limited opportunities available to improve soil conditions in treed landscapes, every effort should be made after renovation to protect the soil. Activities within elm plantings should be restricted through the permitting process to passive recreation and visitor use managed by physical barriers and interpretive signs. All activities should be avoided when the soil is wet. Wherever possible, confined root spaces, such as those in walkways, should be expanded or linked to a greater rooting area by removing or bridging root obstructions. Particular attention should be given to newly planted elms that have been in the ground for less than three years. New elms are prone to drought stress and can become susceptible to breeding attacks by the elm bark beetle. Transplants should be watered frequently, particularly during drought."

Tatnall - perfect reference to the National Mall because I was just about to mention they used a non-organic, permanent soil additive there to help prevent compaction. This used to be discussed extensively at the Davisson Golf website as they were the vendor of the product used. (as in, back in the late 1990s!)
So there are a variety out there, Turface being the most prominent in this country. Although there are varying opinions about which are most effective. In a few years when I develop my next 1/4 acre area for rhododendron planting, I might rototil in something else. Maybe Permatil, I haven't decided. Their roots are even more sensitive about oxygen availability and aeration, especially in a hot summer climate, than typical trees or forbs. For the current 1/4 acres of rhodies I used turface for one another and permatil for another smaller area. Haven't seen much difference yet. I also created a small holding pond just by scooping up some soil w/my FEL. It prevents heavy rains from the slightly higher area from drowning the rhododendrons in the slightly lower area. (FWIW anywhere south of New England, the ideal rhodie growing ground would be real slopes, 10% or greater grade, or very sandy soil like Rarefind's. When I bought this place I had no idea I would get into rhodies as I did...due to visiting Rarefind in May! At least I have a very slight slope.)

Golf course and athletic turf management companies deal with these issues all the time. Not sure how your municipality wants to deal with this but it would certainly seem wise to put out the project for RFP and see what you get. Ultimately, improving the soil profile for grass is not that different than improving it for trees. Presumably you just want to go a bit deeper but again for a project of this nature, maybe a little money spent on a consulting engineer or soil scientist who has dealt with something similar would be money well spent.

Just looking at the situation...I'm also wondering if your average old-school Georgia farmer might have some suggestions.

There are exotic decompaction machines used by the golf course industry, surely. But I've also seen video of real farm tractor pulling a HUGE middle plow, that must go down darn near 3'. Even a dinky little Kubota subcompact like mine can pull a 6" middle plow through 2-3" maple roots. I'm wondering how a farmer might improve this if he thought he had to grow crops on it. Gigantic middleplow, going back and forth over the entire field to bust up the soil? Then regrading and tilling the top? Oh well, interesting project, keep us updated.

davidrt28: I find your comments about the use of Turface vs. Permatil in areas for rhododendrons very interesting. In my own experience, Turface, presumably because it actually absorbs moisture, has sometimes led to overly wet conditions. Permatil is not available locally so I've not tried it. My own garden is steeply sloped, but for particularly finicky species such as members of the taliense I have found the best mixture to be coarse organic matter - usually bark and conifer needles - plus at least 10% pea gravel. No native soil, just this mixture to a depth of 8 to 12 inches.

How about this method from an Atlanta tree company?

"Let me suggest an alternative to you which is probably more cost effective, and will create an evenly broken up area through which water should move more evenly. We have a machine called an AirTech which is basically a pneumatic soil probe that is driven into the soil and then laterally fractures the soil using high pressurized air to create pore space. This can be done at any depth the probe can penetrate, up to 3', but on a heavily compacted site, we can usually only get as deep as 12" or maybe 18". Then, with the probe still in the ground, we inject a slurry of certified organic bio-fertilizer that is designed to stimulate the colonization of soil microbes. Once the pore space is created and microbes are present, then the rest of the soil is broken up via root growth of the planted trees, earthworm action, and additional microbial colonization. We have treated countless properties like this with great success, for both newly planted trees where establishment is desired, and existing mature trees where root regeneration is desired to remediate root loss during construction."

There's just so much information to cover here. I feel like we need to write a book to do the topic any justice. I'll add some thoughts...

The mall restoration piece, above, mostly covers an attempt, where trees are already established, to address some of the problems caused by soil compaction and to prevent or reduce further compaction. The piece does not address drainage. By drilling holes down through soil layers, some aeration is achieved. The degree to which this will help depends on lots of factors like soil type, amount and coverage of holes, and factors associated with time (how long the treatment will provide benefit, etc). I've seen many articles about this sub-topic, and there's just to much to completely cover here. The bottom line for me though is that it's not a miracle cure in many situations and the effects are generally considered temporary unless the treatment process is continued. Drainage is only positively affected if the holes penetrate far enough to enter soil layers where better drainage is present. Even that will depend on a variety of site and case specifics. I did notice that there was a recommendation to address soil compaction, over a large area, before planting, when trees were not already present. Again though, overall drainage is not directly addressed.

The procedure introduced by the Atlanta based tree company would also only temporarily, at best, address some of the issues associated with compaction. It would do nothing, at least nothing positive, for drainage. I'm not familiar with the specifics of their proposal, but I have seen similar recommendations/jobs. At least for now, I'm just going to say that I am less than impressed, for a number of reasons, with what I think they are proposing.

I know that the University of Georgia has a department of Crop and Soil Sciences; have you considered asking them if someone there might be able to contribute to your planning? I feel like I have a reasonable understanding of the basics of soil drainage and so forth, but I have pretty limited experience in projects even close to yours (especially in size/scale).

What may be seen as the first problem with use of organic amendments for permanent plantings is that these decompose and disappear long before the life of the planting is over. To me that defeats the purpose of using them right there.

...but if you can design the area for good surface drainage to start with and improve the soil long enough tor trees and the proper plant cover (some types are excellent, natural ways to address soil compaction problems) to become well established, nature can hopefully take over from there and the area can take care of itself over the long term.

Darn. Thought I had a solution. Ok, so the only way to improve above surface drainage is through grading. Below surface drainage cannot be helped without mass amendments. But mass amendments raise the possibility of actually harming proper drainage if the entire site isn't amended, and even then, we're messing with the subsoil, and you just don't know what that might do. The AirTech treatment has the advantage of not dramatically changing the subsoil in different sections, which I read, Brandon7, as one of your main arguments against amending. So far, so good. The person at the company said that fissuring the soil at multiple levels and multiple areas in rings around the root zones, beginning at the actual planting hole--like some kind of Jedi version of fracking--would have the effect of improving water flow AND would introduce important microbial development which would encourage root growth outward. So I though that solved some of the problems. I think you're exactly right that we'd need to repeat the process as much as twice a year, but maybe more like every year or so. So that's a problem. But, again, you don't like amending. So I'm back at the beginning. One last thing: the person with AirTech did say that in addition to the treatment, we should come in with two inches of good topsoil and another two to four inches of mulch on top. He said that this would work its way downward. He also said that mixing 5-10% organic matter into the planting hole wouldn't be a bad thing, but it's not necessarily vital.

>but if you can design the area for good surface drainage to start with and improve the soil long enough tor trees and the proper plant cover (some types are excellent, natural ways to address soil compaction problems) to become well established, nature can hopefully take over from there and the area can take care of itself over the long termIt is the improved aeration that aids establishment, not the amendments.

...but, the amendments will help to improve aeration, while also adding fertility (modest, I know) and heightened microbial activity to the site. These are improvements for what you're trying to do.

The fact that organic materials decompose is not a drawback to their use, excepting in some specialized container systems, where the plant will remain in the container beyond the life of the original organic amendment. That doesn't apply here.

30 ft. is a decent area to amend. I seldom find myself disagreeing with some of the gentlemen above, but this is one such time. Once the trees do establish, they will add organic matter to the soil via normal cycling of feeder roots. Should we then view this simple fact as a problem? Of course not. If the grade is well set, the planting is done in a sort of bed-not berm-with decent OG content, you will have done due diligence. And compost, while not 100% organic matter, is still the all-around best choice for OG. Then do a mulching over the top when trees are installed. At this point, assuming the trees are viable, they should begin to do the lion's share of site modification themselves.

+oM

Ok, here's the new, new plan:

Rip the bed to twenty feet wide with a subsoiler. Dig 20 feet wide planting holes in the native soil and plant the trees at 4" grade and connect each hole with a 10 ft. wide connection. Cover with 50 yards compost plus fertilizer. On the second day, till 10 radius around the elms, blending the compost and fert down to 10-12". That's about a 10% mix. Add 3" mulch.

I mean, the perfect solution would be to find a new spot out in the forest where no man has stepped. . . but we're stuck with packed, compacted clay.

Tatnall, the AirTech treatment is actually likely to decrease drainage, at least in many situations. By adding amendments in pockets and layers, inside the poorly draining subsoil, drainage down into the subsoil is encourage but drainage from there may actually be inhibited. You may end up with saturated soil for even longer periods of time. The treatment might, depending on specifics, aid in root growth and plant establishment.

When I mentioned improving the soil (in response to Bboy's post), I wasn't in any way talking about improving drainage by amendments. That can be done, but what I was talking about was breaking up the compacted soil. If you can produce a more favorable situation for plant roots, even temporarily, then the added plants (trees and maybe some really good, working covercrop) can get a foothold and start improving things themselves. Starting the trees and/or covercrop on a brick is more difficult.

I'm still thinking that the UG Crop and Soil Sciences people might be very helpful. I've had mixed results from such institutions/people with projects I've worked with, but ya never know until you ask.

I'm in contact with the extension office, but I need to send off a soil sample first.

The problem I see with simply ripping and breaking soil up is that within a year or two, everything will compact again. So a light amendment might help keep things from compacting so quickly, and, of course, a wide top dressing of mulch.

No point in a light amendment, as it won't do anything - that's like drinking a thimble of beer to try and get relaxed. And no point in any amending anyway, as the effect it has is not an improvement - unless you are trying to grow vegetables.

DO mulch generously after planting. No need to dig in the organic material to increase microbial activity etc., as mulching provides the same benefits - in the natural style of litter falling to the forest floor, something that the soil system are predisposed to work with.

Unlike the tilling in of bulk organic material that is not very decomposed.

This amending thing really is a sacred cow.

The problem I see with simply ripping and breaking soil up is that within a year or two, everything will compact again.

Not really.

A former parking lot is seriously compacted soil. However, when most people, particularly here, are talking about compacted soil, that isn't really what they mean. What people are usually referring to when they claim they have compacted soil, is hard soil.

So when/if you loosen up the soil, it isn't going to recompact unless somebody starts driving on it again.

I think mad gallica is correct about that. That's why I'm pretty sure the people who work in this field (golf and athletic turf managers, among others) must have established routines to deal with these situations.

Large area amendment with something like Turface or Permatill probably helps hard soil in certain circumstances. Fixing this OTOH will require some seriously heavy duty equipment: but without the action of other heavy duty equipment, it shouldn't go back to the current state...

We have bad soil all over this area--or at least compacted and/or heavy clay soil. We've got trees planted in 1993 away from the parking lot area that look like they were planted in 2005 or later. It's all heavy clay. If you dig a foot or so down, you're in hard-pan clay. They did construction out here, dug down a few feet, and found some shelves of clay that were as hard as rock.