Forestry, Silvopasture and Agroforestry

Getting tree planting sites ready for next spring

My oft spoken modified proverb: “The best time to plant a tree is 20 years ago, the next best time in 1 year from now”

Laying down a mulch of shredded wood at least a year before planting a woody species will create an ideal soil habitat for the plant whether it be a bramble, shrub or tree. Plants uptake nutrients via a symbiotic relationship with mycorrhizal fungi. A layer of woody mulch well before planting facilitates the fungal dominance in which woody species thrive as well as invigorate soils with nourishment from the decaying wood.

Plus some of my trees planned for next year need a sulfur application to acidify the soil lowering it to the ideal pH for that species. Sulfur needs months to be broken down in order to actually have an effect on the soil.

My process was as follows:

Weed wack all plant matter to the ground, rake out the clipped plants if they are significant

Apply the calculated amount of sulfur (tables can be found in this post)

Return any raked clippings (if applicable)

Lay down cardboard or paper to smother the existing turf. This biodegradable barrier will breakdown to humus given time!

Pile on as much mulch as you can spare

Come spring time, your back will appreciate the more workable soil (although I don’t recommend amending the soil or loosening it mechanically by digging an oversized planting hole. See here)

Pictures:

Removing most of the above ground vegetation:

IMG_20150911_174256

The clippings are then raked out, sulfur applied (for the sourwood planting sites), then the clippings are returned.

Cardboard or sturdy paper (paper grocery bags in my case) are laid down to smother the vegetation then mulch is piled on top.

The [almost] finished site looks like this:

IMG_20150922_154122

More info:

More tips to ensure success with trees

Where to find mulch for woody species

Fungal basics of mulching

How to think like a plant to be a successful cultivator

How to think like a plant to be a successful cultivator part 2

Mulch Matters 2: Different Types of Mulches for Different Types of Plants

Compost Matters: Garden Compost vs. Orchard compost

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Garden

My strategy for acidifying soils

In November, my soils tested near a pH of 8 due to the limestone parent and its alkaline calcium contributions. I figured that laying down partially composted horse manure with its pine bedding, mulching it, and letting it compost for another 6 months would help buffer the pH into more manageable levels. Knowing that the blueberry bushes were set to arrive later in the week, I used my quick and imprecise soil kit:

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Uh oh!

It is apparent that more action is required.

What acidifying soils actually does:

For some reason landscape designers absolutely love putting Pin Oaks in the soil islands in parking lots. No consideration is given to the requirement of these trees to grow in low pH soils. As a result, the trees can’t obtain iron through its roots and wind up chlorotic, or yellowing sick leaves year round. This is the same condition that blueberries will face in too alkaline of soil.

Remember anions and cations from high school chemistry? I’ll spare the most gruesome of details regarding what is going on in soils with varying pH. An alkaline soil is high in cations like calcium or magnesium effectively ties up necessary nutrients in soil like iron due to a low anion exchange capacity.

Further exacerbating the iron uptake issues is that iron is immobile meaning that within a plant, iron cannot be moved from old growth to new growth. The iron requirement in every bit of growth of new leaves, fruit, buds etc. must come from the soils. That is why pH is such a big deal with plants like blueberries!

Acidifying soil strategies:

Attempts to acidify soils can be broken into two categories: Temporary and Slightly Less Temporary. Biologically healthy and active soils have tremendous buffering capabilities in regards to pH. Whatever the motivation to grow a plant like blueberries in alkaline soils like I am doing, the gardener needs to understand that the soil will need constant maintenance to maintain a low pH.

Slightly less temporary acidification means

Slow release soil amendments will release acid as the soil microbes process the parent material of the amendment. The only organically-approved material here is elemental sulfur. While certainly not biologically organic as one would intuitively assume, it still gets organic certification because is is nothing more than a basic element off the periodic table that is found in soils. Application rate depends on the current pH and the structure of the soil. The below table provides a guide with units of pounds per acre. The table below contains the figures once I converted to pounds per 1000 square feet (source):

 

Table 1. Rates of elemental sulfur required to decrease soil pH to a depth of 6 inches.
Desired change in pH Application rate based on soil texture1
Sand Silt loam Clay
———————– lb S/A ———————-
8.5 to 6.5 370 730 1460
8.0 to 6.5 340 670 1340
7.5 to 6.5 300 600 1200
7.0 to 6.5 180 360 720
8.5 to 5.5 830 1660 3310
8.0 to 5.5 800 1600 3190
7.5 to 5.5 760 1530 3050
7.0 to 5.5 640 1290 2580
1 Assumptions—cation exchange capacity of the sandy loam, silt loam, and clay soil are 5, 10, and 20 meq/100 g, respectively; soils are not calcareous.

 

Table 1. Rates of elemental sulfur required to decrease soil pH to a depth of 6 inches.
Desired change in pH Application rate based on soil texture1
Sand Silt loam Clay
———————– lb S/1000 sq. ft ———————-
8.5 to 6.5 8.5 16.8 33.5
8.0 to 6.5 7.8 15.4 30.8
7.5 to 6.5 6.9 13.8 27.5
7.0 to 6.5 4.1 8.3 16.5
8.5 to 5.5 19.1 38.1 76.0
8.0 to 5.5 18.4 36.7 73.2
7.5 to 5.5 17.5 35.1 70
7.0 to 5.5 14.7 29.6 59.2
1 Assumptions—cation exchange capacity of the sandy loam, silt loam, and clay soil are 5, 10, and 20 meq/100 g, respectively; soils are not calcareous.

 

 

As sulfur takes months to have an effect of soil pH, I regret not applying it in November with the installation of the compost. I did rent a tiller and worked 8 pounds into my 80 square foot blueberry bed. I will continue to topdress with elemental sulfur (under the mulch layer). Now I’ll have to work slowly and carefully with the living plants using temporary means while the sulfur goes to work.

Peat moss is another amendment that has been proven to significantly boost blueberry yields. Personally, I don’t think peat moss deserves a place in horticulture as it is a not renewable resource and is extracted from fragile ecosystems. Here is a good article on the subject.

Temporary acidification means

Acidifying fertilizers are one method to maintain soil pH. As there is a large livestock feedmill nearby, I use 50+ pounds sacks of cottonseed meal ($12) as a fertilizer that both provides nitrogen and acidifies soil as it breaks down. It is pelletized which I initially did not like, but after the first rain since applying 200 pounds of it, the pellets explode in volume and hold quite a bit of moisture.

Acidic irrigation is another part of my strategy. I use 2 tablespoons of the cheap distilled white vinegar per gallon of water to irrigate the root zones. I use a much more aggressive rate to apply between plants where no roots yet exist. I repeat this weekly as vinegar only temporarily ties up calcium! Oak tea is an experiment I am currently trying to find a more biological approach than distilled vinegar.

Acidic mulching: mulching materials like pine straw/needles have long been recommended to help acidify soils. While acidifying soils has tossed some obstacles to my biological approach to raising food crops, I still want to mulch in a manner that promotes mycorrhizal fungal dominance that all woody species need. Therefore I mulch with shredded wood from tree tops but apply elemental sulfur below the mulch.

 

Conclusion

The best time to acidify soil is at least 2-3 months before planting. I missed the boat here and now have that added complications of working with living roots that will be burned by a direct application of strong acid. I hope to be able to gradually lower the pH of the soils before the bushes begin producing berries.

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