Composition #
For nearly every crop described in his book French Intensive Gardening, John Weathers explains that the garden beds are covered with a layer of “fine sandy/gritty mould”. When he explicitly describes it, it’s usually a mix of “spent manure” and “gritty soil”, and may be passed through a sieve.
While he doesn’t mention the size of the sieve, other writers have mentioned a half-inch sieve. Some modern British references suggest using 1 cm mesh for a soil sieve, so it seems not much has changed in these recommendations. Mostly, the “fine” and sieved soils are used for root crops like carrots, turnips, radishes, that can be malformed if they hit rocks or other chunks in the soil.
The manure he mentions is almost always horse manure, a byproduct of the many horses used for transportation in the cities at the time. This manure is either aged in the open air or first used to heat a hot-bed and then reused to grow in. “Hot” manure should never come in contact with the plants. Once in awhile he also mentions cow manure and “night soil”—a euphemism for human manure.
In addition to manures, he mentions “leaf mould”, which is simply decomposed/composted leaves, and occasionally just general vegetable compost.
The proportions of organic matter to soil vary only slightly between crops. Sometimes it’s 2 parts mould to 1 part soil; sometimes 3 parts to 1 part soil. When describing “gotte lettuce” he says the soil should be sandier than for “crêpe lettuce”, but doesn’t spell out what either one requires. Given that these were mixed in the field, the proportions are most likely by volume rather than weight. In practice it was probably something like, “mix 30 shovelfuls of composted manure with 10 of sand”.
Our Experience with Modern Sources #
We currently use a mix of Quikrete Medium Sand and the Earthgro Steer Manure Blend, both available at a number of local stores. The mix is 50 lbs of sand (roughly .75 cubic feet) to 2 cubic feet of composted manure, mixed in a 6 cubic foot wheelbarrow. That falls between the 1:2 and 1:3 mixes.
Given that these proportions provide plenty of organic matter to provide for structure and drainage, there’s some room for variation in which kind of sand (and soil, for that matter) is used.
As for the sand, this particular sand meets the US Golf Association specs for their root zone mixture they recommend for putting greens—which often has the grass growing in pure sand—so it’s certainly well vetted for growing plants in.
For the manure mix, Scotts/Earthgro guarantee a minimum of 50% aged steer manure with the rest as compost. Occasionally there are a few sticks and pebbles which are removed by hand. This is a place where a soil sieve could prove useful.
At some point we will try some other manure, composts, and maybe even decomposed leaf mould from the local oak trees, but in we have successfully grown a few crops using these locally available commercial supplies.
Thickness #
The main difference on a per crop basis seems to be more a matter of the thickness of the mix on top of the bed, rather than its composition.
It also seems hot-beds always have an extra few inches to buffer the roots from the hot manure.
A few examples Weathers called out:
- Carrots 6” over a hot-bed
- Cauliflower “frames filled to within 6 in.”, and for hot-beds:
“Early in December the hot-beds are made up, and a layer about 7 in. thick of rich sandy loam and leaf-mould, or old manure and sandy soil (three parts of manure to one of soil), is spread evenly over the surface.”
- Cucumbers 6-8” for frames over a hot-bed, and 8” for cloches over a hot-bed
- Endives 5” over a hot-bed
- Crêpe and Petite Noire Lettuces 1+”; and with frames, filled up to mould within 3-4 inches, then an inch of sandy mould; 4” over a hot-bed
- Gotte Lettuces 4”
- Cos/Romaine Lettuces 1” in the open; 4-5” over hot-beds