Soils
Pull a soil analysis for any large landscaping project, it will help document your failures on the bad sites. Nothing makes you look less professional than to have all the plants on a site die and not know what happened. If you know you have a 'ZINGER' it will allow you to plan a battle plan to correct it or plant to it. A complete analysis costs less than $100.00, no big deal on most installations.
What is pH?
pH is a measure of acidity in the soil (hydrogen ions). pH is logarithmic, a pH of 6 is ten times more acidic than the neutral 7, a pH 7.8 is about eight times more alkaline than a neutral pH of 7. The confusing part is differences within the range, such as between 6 and 7.8. The numbers are multiples, so take the ten and times eight, or pH of 6 has about 80 times as many hydrogen ions as pH of 7.8. Conversely, pH 7.8 has 80 times more OH- than pH 6. H+ and -OH make water (neutral), the balance of available units of each is pH.
Make sure you have the appropriate plant material.
Plants are adapted to certain ranges, some acidic (firs, huckleberries), some alkaline (saltbush), if you plant an acid lover in an alkaline area the the leaves will have brown or black margins on them, before they drop off. The plants, generally, will lose their leaves within a few weeks, decline and die. Plant an alkaline lover in acidic soil they usually have yellow(chlorotic) leaves, then burnt leaf margins, then rot off and die.
Things to look out for.
Sodium
is an element that plants do not like much. Leaf burn starts
showing up at about 100 ppm (parts per million). 250 ppm kills a
lot of stuff, 500 ppm sodium only supports salt tolerant plants.
See coastal
salt marsh plants.
Boron, as little as a few ppm will kill many plants.
Nitrogen, Phosphorous, Potassium and most of the other stuff is not important unless one of them is WAY off. The only low problem so far was Potassium at 2 ppm ( should be at least in the 20's or 30's). A few bags of Potassium sulfate moved the numbers up to planet earth. When the site has one of the way off values you got problems that will not go away unless helped a little. Low numbers can be brought up, high numbers have to be designed out with plants.
The code words are:
I planted a few plants out, but they all died;
The last contractor before killed all his plants here;
Our neighbor has had a terrible time trying to plant his place; everything died.
My favorite two so far are: 'you might have a little trouble digging out there, that's where they used to park the oil trucks'; and 'that ground sure looks hard, that's about where the old stage line used to run'.
If the area has no bushes or trees and all that is there is grassy weeds, why? It may be the soil or water. In California houses and subdivisions are being put into areas that farmers couldn't farm because of poor soils, high boron, high sodium or rock.
If the soil report comes back with Boron higher than 1 ppm, pH higher than 8 or lower than 5, and Sodium greater than 200 ppm, you'll have to do some planning to figure which plants can grow there. On many sites whatever is native there may be all that can grow there. Have a water analysis done also if a soil analysis comes back bad, and then seek help.
Options?
Site specific planting can be cost effective if everything else dies.
If you have one of these bald problem areas, have a complete report done instead of a partial one. Sometimes there are problems that are not supposed to be in the area. (Your garden is special because the fill came from the nuclear power plant's holding pond.)
Look long and hard at soils with hard pan, with serpentine, with salt spray, with any white surface deposits(or any other color for that goes, one site had a rainbow) or with a mining operation going on nearby. It is amazing that people do not wonder about their soil with a mercury, borax, lead, salt, gypsum, or other mineral deposit on the site or next door.
If the site is bald, ask about the history of the site, it can be important!
Native plants have adapted to these soils and sites. Native plants have both mechanical means (sheathing) and chemical means (greater nutrition and depositing the chemical in the fungal parts and sloughing them off) to help tolerate high soil toxicities.
How to kill the mycorrhizal fungus. BAD!
The disturbance of the subdivision is enough to create instability in the native community, never mind restoration of the mitigated areas. One of the researchers in Australia tested backyards for mycorrhizal presence, none. If the site is torn up, heavily amended, and plants form all over the place planted together the plant community is replaced with a ruderal (weed) community.
Hayman (1983) reported that passing the soil through a 9.5 mm (about 4 inches) sieve destroyed the soil mycorrhiza's hyphae and that the hyphae was needed to reestablish grasslands, spores did not work. If you till or otherwise work the soil below 12" you will kill most of the mycorrhiza. (Protecting it, will save you time and your customer's money.)
Do not amend the soil. Get restrictive on what is planted if the soil analysis comes back bad. Scraping off the alkaline domes to replace the top soil, amending to counteract the 'bad' soil, does not work. 2 inches of soil sulfur on top of 300 feet of a lime dome will not make the lime dome go away. Putting 12" of new soil on the old, kills the old soil, the top soil also dies, and you create an inversion layer at the interface. A triple whammy. If the soil report is bad, work with the plants that are in the same soil, same area, same plant community. Pick the best looking ones, have them grown and design them into the landscaping. You will save yourself lots of money.
If the site is covered with rocks, why not make a rock garden? If the site is on lime, why not make a lime-loving garden? (This is one soil/climate where you should look at the plants in the Mediterranean region that grow in the South European shrub basic community. You can get some more variety.)
If
there is no community there, match the community you're going to
create to the soil and climate. If you are given a subdivision
that has nothing but bare dirt that is very acid with poor
drainage along the coast, maybe you should look at making the
whole design work around this. Try an oak or pine forest around
the houses according to how much water you have, transitioning
from the dry areas through 'communities' to the wetlands around a
catch basin.
The healthier this soil and its plant communities becomes, the more suppression there is of the alien weeds and plant pathogens. "The greater the complexity of the biological community, [including the successional stages] the greater is its stability. At the very least, cultural practices should be selected that do not environmentally upset the suppressive communities of microorganisms that help defend plants against pathogens." (R.J. Cook) Even non-mycorrhizal plants benefit from this type planting often becoming partially mycorrhizal.
Sites high in metals will not support desert species, look to conifers and chaparral species to help.
Sites with moderately high salts support both desert and chaparral. As the salt level goes higher you have to use specific species, predominantly VAM desert/shadscale types or dryland halophytes. If the moisture is constant, certain non-mycorrhizal plants will be in the salty wet spots going to VAM in the dry spots.
One of the normal procedures for developing a house site is to pile the top soil in a pile until the house is done and then put it back. The soil community die after about four-ten years when you do this. If on the other hand, you plant it with the pioneer species, when you move it back the soil community will often be viable.
If the stockpiled soil is blended in with the remaining soil there will not be much soil activity. Spread the stock piled soil back as it came, hopefully only moving less than a 1 foot depth each time (a foot off and then back on) and when the soil is dry. Never work wet soil! Keep a native wildflower cover crop going on it as best as possible. Control the weeds, the system sees weeds like a human body sees a staph infection.
Do not change the soil levels if possible. Changing the level more than 1-2 feet will greatly alter or kill the soil ecosystem. This is the primary reason why oak trees die when you change the soil level.
Compacted soils are not desirable. Rolling a roller over a site can reduce/alter/destroy soil microflora. That is why there are wagon tracks in the desert after a 150 years and many freeways can support weedy species so well.
An interesting note: the only soils that are primarily bacterial based are soils where "modern" agriculture has occurred, sewage fields and disturbed weedy sites. Native soils are fungal based. Native systems and row crop type agricultural/weed systems are two opposing ecosystems. Edith Allen showed that after 150 years alien grasslands did not become native on their own.
