Thursday, March 15, 2012

Understanding the Proper Soil Make Up in Landscaping or Habitat Restoration

The best way to answer this question is to relate some of my personal experience with just this question. Sometime you cannot learn except the hard way. Hopefully the readers here won't have to go through such disappointments, but like many kids, there may be no other way for some folks to learn a lesson any other way but "The Hard Way" - The right plant in the right soil?

The question of course is no doubt dealing with soil requirements for which almost every plant may have specific requirements for successful living. My one experience dealing with a small-Medium tree called Tecate Cypress (Cupressus forbesii) which has some important and unique soil requirements if you plan on using them in your urban garden soil. This should be a great illustrative example of what we're talking about with reference to this question with regards what is right as well as wrong. 

One of the best ways I've ever found in successfully learning about various plant requirements is to actually go out and visit where they grow in the wild. The make up of the soil where Tecate Cypress grows in the wild is what most home gardeners would consider some of the nastiest soil for gardens in the world. Sure enough, their native habitat's soil is rugged, rocky, decomposed granite and even a fair amount of Adobe characterisitics in this soil which is sticky when wet, but hard as a rock when dry. Yet, Tecate Cypress actually succeeds in this nasty looking soil environment. Actually it thrives there. One of the reasons it does thrive in these type of soils are the mycorrhizal symbiotic relationships for which the subject matter of this particular blog deals with. Yes, even in these soils an underground  "Earth's Internet" plays a major role or they wouldn't exist there in the first place. However, there is yet another important reason these plants benefit and indeed actually thrive from this type of soil. It's called foundational structure.

Tecate Cypress for the average gardener in Southern California is a bit of a mystery tree. Very few people have ever seen it and for those who have it is a bit difficult to find at your average Nursery unless that Nursery is specifically a California Native Plant Nursery. One reason most people have never seen it in the wild is because for the most part it is fairly inaccessible in it's native habitat. The terrain is steep and often there are very few trails or roads for which to visit. And if there are roads leading to them, most of these are in closed off wilderness areas and if you do find a way of getting there you must do so through private land and the owner's permission. Yet for me it is one of the most beautiful of Cypress trees. The younger trees have a bright green foliage and the bark is a cinnamon red, much like that of a Manzanita shrub. If I get a good link pic for the bark I'll post it in the future, but you may be able to google image it. 

red bark of Tecate Cypress
It was one of my hopes to establish a unique Tecate Cypress woodland garden theme in my mother's landscape. However the tree has one flaw and that can be fatal. As a seedling and indeed, young tree, it is exceptionally fast growing. So much so that it's above ground branching structure will out perform it's own root system and become very top heavy. In my mother's backyard I built up a rather large retaining wall planter to construct my woodland garden. My mother's property and surrounding hectares of land around this were created from alluvial floodplain soils of sandy loam deposited over 1000s of years from the canyons above an area called Rattlesnake Mountain in El Cajon CA. Perfect soil for gardening, in fact this particular beautiful sandy loam soil is several meters deep. However it was my experience the second year when we received a heavy rainstorm and the winds blew some of the trees over or at least bent them over to the extreme. It should be noted however that in their native habitat the high winds are far worse, but the tough soil structure keeps the root system sturdy and also the accompanying chaparral act as a sort of plant staking support component. Take a look at how this works from the picture below of Cuyamaca Cypress with same soil requirements.

Cuyamaca Cypress with Chaparral Support System
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Tecate Cypress with Chaparral Support System
This past year my wife and I flew back to San Diego from here in Sweden and I had to cut all of them down but one. I felt horrible for doing it but it was necessary. Here's a picture below of this very planter location back in the year 2003 and you can see in the picture how some of the trees were already starting to lean over a bit. This is because the soil was very loose and sandy in it's structural make up. This may have been okay if the natural support system of a chaparral environment was in place, but it wasn't. Often times in a garden urban landscape setting we have to artificially stake up trees which would have been no problem in a wild setting.

Sadly in 2006, just before I moved over to Sweden, we had a very windy and rainy springtime storm in April 2006 which knocked over most of those trees. It was necessary to pull them back up and stake them with large posts to keep them upright, but it was difficult and the multiple stakes were aesthetically unsightly. Unfortunately this was necessary if I wanted to save them. There were further storms the following years and sadly that soft sandy loam perfect garden soil just wasn't strong enough to support all that top weight. With the "Earth Internet" planting strategy establishment game, I never use ANY chemical fertilizers what-so-ever. I did inoculate all of the plantings with a mix of both endo-mycorrhizae and ecto-mycorrhizae blended fungal spores along with beneficial symbiotic bacteria in the mix from a company called Plant Health Care Inc (PHC). I also heavily mulch around all of the plants. This not only adds a natural carbon feed to be downloaded by the complex sophisticated  mycorrizal network grid which exists underground, but it then is uploaded by the plants which transfer these beneficial nutrients which were made available to them from this grid. Yes you could use fertilizers to accomplish the same thing, but the health content wouldn't be the same and any mycorrhizae will actually disconnect and disassemble the healthy grid in the presence of heavy chemical usage. On an interesting note, it was in 2005 and the mulch I used came from the tree trimmings of some Canary Island pine trees from my work place and for which numerous volunteer seedlings popped up before I moved to Europe. I left them to grow naturally and had to thin the ones I didn't want. The result is that these trees which eventually replaced the Cypresses are now close to 30' high since I left in May of 2006. It's their nature to grow fast as well, but I'll have more on this in a future post. 

Here are some helpful ideas and very easy to understand tips on the benefits of an "Earth Internet" mycorrhizal based system by Linda Chalker-Scott an associate professor in the department of Horticulture and Landscape Architecture at Washington State University

"Why does the myth of phosphorus-induced root stimulation persist? The answer probably lies in theeffect phosphorus fertilizers have on mycorrhizal relationships. When plant roots are in low phosphorusenvironments, they exude organic acids from their root tips. These acids allow mycorrhizal fungi topenetrate the roots and form the networks that assist plant roots in taking up water and nutrients.Mycorrhizae are particularly adept at extracting phosphorus from the soil.""If phosphorus levels are too high, however, the roots do not exude the organic acids and mycorrhizalconnections do not form. This forces the plant to put more resources into root growth to compensate forthe lack of mycorrhizae. So in a sense phosphorus will increase root growth – but at an added cost to theplant. The resources expended by the plant in growing additional roots to take the place of mycorrhizaeare not available for other plant needs.""Shrub and tree species that are mycorrhizae-dependent have a difficult time surviving in soils wheremycorrhizae cannot develop. In particular, seedlings and newly transplanted materials are less efficient inabsorbing water and minerals from the soil and are more likely to suffer transplant shock than plantswhere mycorrhizae are present. Adding mycorrhizal spores to soils where phosphorus is too high isineffective – the spores will remain dormant."

On this same question and subject of soil structure, I had another unique experience in working with the soil on my sister's property in a brand new housing tract built in the year 2000 in Lakeside California. Like most newer housing tract developments in Southern California, most of the good agricultural land like my mother's property which use to be an Orange Grove are just about used up, but these newer tracts are built on steeply sloped hills or mountains. The building plots have certain specific compaction requirements which are necessary in order for the house to have a stable foundation. This of course is only logical given the sad experience by many folks who have homes in older developments which have been lost in well known southern California landslides as a result of poor clay soil accounting or consideration of the soil's structural make-up which no doubt was ignored in favour of making a quick profit in a desirable location, usually somewhere on the sea coasts where there is often a lack of solid bedrock for stability. My sister's property was prepared by the contractors who scraped off all top soil, used dynamite to blast through the granite bedrock and crushed this rock into various sizes only to be formed into the future housing pads and then compacted with heavy machinery for stable building foundations. 

Most modern garden soils are like rammed earth

After the houses were built, they proceeded to apply a layer of brown Adobe looking earth and actually called this topsoil. Not only is this a major obstacle for the establishment of the usual horticultural selections you buy at your local retail nursery, but it is also a huge challenge for native plants from the same area. The soil structure is almost like that of Rammed Earth Construction  which is a new form of eco-designing house construction which has lately become popular for some. So your soil is almost like a solid concrete block wall. Water percolation is almost nill.

I found this out when constructing the hardscape which consisted of irrigation layout, retaining wall, pathway and step construction. I also found it necessary to create and build up raised planting beds and retaining walls around the perimeter and corners of her property. In the area where the lawn was I had to dig out countless large stones in between very little decomposed granite soil which was beneath the 6 to 8 inch phony labeled top soil added for nothing more than what I'd call "Eye Candy". I'm not at all a promoter of adding soil amendment to any tree or shrub plantings. However with the lawn it was a must. We had 5 deliveries of large bins of soil amendment from the local Home Depot. The work was tough and took a huge amount of extra time. The rock chunks I threw behind the retaining walls and mixed in with the soil there as it wouldn't have mattered to the trees and shrubs I would install there later. As always, I innoculated the ground where I wanted to establish the lawn, trees and shrubs. Interestingly, a healthy and thriving "Earth Internet" mycorrhizal web network will actually over time break down some of this compacted soils, but again, it will take some time 

 The bottom line when it comes to soils, you need first to familiarize yourself with you own property and the ground that lays underneath. Clay soils likewise have their own challenges , but there are plants that will work well in these, but you have to know which ones. If the nursery you do business at actually knows it's local business and has done their homework on what works in that area, then you should be able to get some sound advice from them. Also I have found from personal experience that it actually helps to get in your car and drive around the various local neighbourhoods in your area and take notice of the successful gardens/landscapes and ask questions of those homeowners. Again, knowing your soil and what plants will work is the first route to success and by all means DO NOT forget the benefits of establishing your own underground "Earth Internet"

Stay tuned for more articles and don't hesitate to ask specific questions on this.

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