A semi-underground greenhouse in Brittany:

November 2020, Brittany (1 month):

During part of the preparation of the expedition we were in French Brittany. In exchange for the hospitality, we worked in the garden: extending the chicken coop, planting trees and especially putting in a rich soil for a semi-underground greenhouse.

The main difficulty in setting up the greenhouse is enriching the soil. Indeed, the ground, close to a pine forest, is composed of a sandy soil, very poor in organic matter and retaining few nutrients necessary for the development of plants. It was therefore necessary to enrich or even "create" a new, richer soil. To do this, as the greenhouse would be semi-buried, we removed 60 to 80 cm of soil (to equalize, as the ground is sloping) to replace it with organic materials allowing, by their biological degradation with time, the formation of a rich soil. We have therefore "filled" the hole by strata of different materials:

5 cm of mulch (straw)
10 cm of topsoil
5 cm of nutrient rich material (compost, dry manure...)
10 cm of nitrogenous material (fresh grass clippings, nettles...)
10 cm carbonaceous material (straw, oak leaves...)
10 cm of nitrogenous material (fresh grass clippings, nettles...)
10 cm Carbonaceous material (straw, oak leaves...)
Original soil

The 10 cm of topsoil, almost on the surface, allows planting now, without having to wait for the soil to form, which will happen over time.

The advantage of this technique, although it requires a lot of work and an abundant quantity of material, is the creation of a new rich and productive soil very quickly. In addition, the greater the amount of imported material, the longer the soil will be rich and productive. Also, the surface of rich and productive soil will increase by "contamination" (leaching, erosion... which will displace the nutrients).

Result in May 2021: