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Eco-Answers from the Pros: Sustainable Soil Mix

I am a landscape designer with a maintenance crew working on Martha’s Vineyard. We are reviewing our Specifications to update to sustainable practice. I have previously specified for soils to be used for backfilling plants and filling perennial beds a mix of Earthlife Compost (3 parts), peat moss (2 parts), and sand (1 part). Is there a better mix in light of insuring a healthy planet? I have seen 7 parts topsoil to 1 part peat moss in another Spec and also have seen we should not be using peat moss. Thanks for any light you can shed on this.

Mixing soil components 1I don’t use peat moss. My ‘sustainable soil mix’ is to fill a wheelbarrow with the following and mix thoroughly: 1/2 weed free topsoil, 1/4 composted cow manure, and 1/4 traction sand. I have used this “concoction” for many years and have had great results. Water drainage is great and the manure serves as a good nutrient source. You can always substitute the manure with some other kind of compost.

Bruce Wenning, Horticulturist, The Country Club, Brookline, MA

I, too, don’t use peat moss both because of its sustainability issues and because it is hydrophobic and can be very hard to rewet if dried out. John Sabuco, Best of the Hardiest, dug up peat moss 12 years after using it in planting holes and found it largely unchanged and unpenetrated by tree roots. I can understand you’re need to use it though, since it’s easy to transport if not wet. Have you looked into coir (coconut husk meal)? It’s also easy to transport but breaks down more easily and is renewable on a less than epoch time line.

Not sure this will help since inland is so different, but have you looked at locally composted seaweed and other local organic debris – even making it yourself from your own property maintenance end of the business?

I split tree installations from perennial installations and manage them differently.

For the trees: I coat all exposed roots with a 1/1/1 mix of alfalfa meal, azomite, and greens, and I don’t use any amendments in the bottom two-thirds of the hole – just the existing backfill with the sides roughed up. At the one-third soil depth layer, I work in some high fiber compost like decomposed wood chip (even bark mulch in a pinch). I add roughly a good shovel full to each half of the hole working into the existing back fill soil. Then I add compost, more high fiber compost and a good quality low intensity organic fertilizer to the top 3” of the hole worked into the remaining back fill. All of this is designed to support fungi essential to the tree’s long term survival and keep the top of the soil open to water and air penetration. This seems to support the fastest and sturdiest response from the trees and allows for a much wider root system than the highly amended holes (that often act like a pot in the ground). I also find it easier to deep water or dry out trees planted this way, and that’s important since so many clients don’t get the watering right.

For the perennial gardens: I don’t know Martha’s Vineyard at all but would suspect you have the opposite of what I have for soil problems. Here in central MA I have clients with mostly clay based soils, but I do have a couple on sand dunes near lakes so I’m going to detail what I do on those two sites.

I bring in loam rarely unless I have to change the grade, and I try to work with whatever soil the site provides. If I do bring in soil or a soil mix (and I prefer a 1/3 compost; 2/3 loam limed mixed) then I make sure that the existing soil is well broken up and the two layers are somewhat physically integrated to help with the long term integration of the bed.

When starting from scratch, I add 2-3” of compost, stone dust (a visual dusting), calcium (check with a soil test if unsure), alfalfa meal (50lbs per 500 sq ft) and work that down either with a rototiller or some other means. Again – this is designed to support fungal populations which will help hold minerals and water in sandy soils – and they need the support – alfalfa meal is essential to get all microbial populations off to a great start.

When planting I adjust the holes to match the plant’s needs. You’re probably planting drought and sandy soil tolerant species so this may not be as big a deal, but inland there’s a really wide plant palette and I have some clients who want a more traditional garden look. This means I beef up the areas that delphiniums, roses, hollyhocks, etc. are going to be growing in with extra compost when planting. I also use a custom-blended organic fertilizer that is low intensity but complex mineralogically worked into the soil around each plant.

M.L. Altobelli, Owner of M.L.’s Greenery in Motion, Westminster, MA

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