Need to improve soil in newly constructed hugelculture

Hello to all!  I have a new hugelculture...actually quite lengthy.  Dug down about to add 2 feet of old logs then mounded about 3 feet of dirt on top.  The problem is it is all sandy soil.  Planted clover and winter peas on it for green mulch and add coffee grounds from a local shop.  I think I might need to plant a summer cover crop for mulch and soil improvement but would also like to try some other plants.  May add a tree or two.  Any thoughts on how to help my sandy soil become fertile soil the most effective way? What summer
cover crops to use in Zone 8.  Thanks to all!

Hi Sue. Welcome to permies. Sounds like you're doing the right things. Some animal manures & buried kitchen scraps would probably help speed things up by attracting some worms & other soil critters. I would simply keep growing in that space & add organic materials as they become available. Make sure it gets plenty of moisture the first year or two. New hugels also need extra nitrogen so legumes are good.

https://permies.com/wiki/redhawk-soil

As many different living plants for as much of the time as possible will feed the microbes that will build stable soil aggregates.

Hi Sue.

If you happen to have clay deposits locally, you could try to get some of that stuff. Alternately, you could buy natural clays in dried powder form and amend your soil with that.

I would just keep applying compost to the top, and make sure you have a good mulch layer to keep wind and sun dessication down. Moisture control is a huge issue here, as the soil life is what will be holding most of your moisture, and not supporting them enough can lead to die-offs and dessication of the whole system.

If you had an abundance of woodchips, you could pile those thickly on the shaded side and inoculate with fungi, probably something easy like winecaps, and put a drip line on it. The fungi would support other soil life and break the woodchips down to a texture that is more suitable for retaining moisture.

If you had an abundance of river rock or other stone, you could dry-stack a double-layer of stone such that warm, moisture-laden air can pass through to a shaded inner layer, depositing that moisture there, which would make most sense to do on the sunward side.

If you nurture the soil life and keep the moisture at the right levels, the soil life will thrive and improve the water retention. If you grow cover crops for a chop-and-drop, you get not only mulch atop the soil, but the root zones below, slowly composting. If you're growing something like alfalfa, for instance, that means roots that go down potentially six feet or more.

If the concern is adding fertility to your hugelbeet, nature deposits nutrients on the surface of the soil. You can work amendments into the top layers, but I wouldn't bother, especially if you've been working on your soil structure already. I would, instead, make and use some of the actively aerated compost extract that Dr. Redhawk talks about extensively in his threads, linked-to above by Mike. To that I would add fungal slurries. If you haven't any interest in culinary mushrooms, winecaps will do well for breaking down woodchips, though I understand they are tasty enough. The compost extracts will infiltrate down through the soil structure, carrying beneficial microbes, as will the fungal slurries, which will encourage mycelial networks to form for biomass processing and materials distribution.

But however you do it, get it wet, keep it from drying, and get stuff in that will both grow in your sandy, unimproved conditions, and will make good cover crops. Growing things and killing them to make soil is the best way, short of importing amendments, to improve your soil.

But don't discount amending what you have. As I said, if you add clay particles, your soil will retain moisture more readily, and will hold fertility better. If you lack specific macro- or micronutrients, trace minerals, that sort of thing, you are unlikely to get them by growing plants, with specific exceptions (if the mineral resources are present but made unavailable by inappropriate soil pH or by death of those bacteria that make soil minerals bioavailable, for instance). A well-reasoned input that boosts your soil life into high-gear and accelerates and/or improves your positive impact or output by improving system health as a whole isn't a bad thing.

But let us know how it's going. Send pictures, and good luck!

-CK

Hello Sue.
I am in zone 7 so my experience is somewhat different but may be helpful. I have about 400' of 5' x 10' hugelculture berms built with cottonwood and sand and silt. The process has been going on about 20 years. Alongside the berms are adobe buildings. The recipe for adobe construction is 8 parts sand to 1 part clay plus some organic matter (mostly goathead plants). I give you this recipe in hopes that you will not add clay to your berm. The rock-hard results are great for building permanent structures for your homestead but not helpful for growing plants. The plants that grow well on the berm are natives grown from seeds that are in the sand already or easy to gather on roadsides locally. Mix those seeds with one part clay and one part compost to make 1/2 inch dry pellets to toss into depressions formed by your boot prints. These depressions hold water and help the plants grow. Eventually you will replace some of the natives (saltbush in my case) with edible plants. Use trimmings from the volunteer plants to enrich the berm. Hold the moisture in the berm with trimmings (keep all organic matter in the berm).
I have success planting non-natives at the foot of the berm where runoff water catches. I use horse manure to enrich the berms with organic matter since this is what is available here. My neighbors fill the wheelbarrow daily and I wheel the manure up ramps to drop the droppings on top of the berm (sheet composting). The nutrient rich runoff at the bottom of the berms has supported the growth of fava beans (great for eating and for compost), irises, fruit trees (plums, apricots, apples, pears, jujubes, cherries...) and extensive crops of garlic. The key is as much organic matter as you can get every year. Eventually (think 5 years or more) if you make catchments for water on the berm or even inject water into the berm with a homemade pvc hose attachment (about 3' long) the worms will take over. This project has been very rewarding and it is worth the effort that I put in years ago. The harvests over the last 10 years have been abundant and steadily increasing. Enjoy the process.
Amy

As amy notes, it is important to avoid adding too much of anything.  But right now you have too much sandy soil that likely has issues retaining water. I think that if you increase the amount of clay in the ratio of clay, sand, and organic material above the "nothing" level to something that gives your soil some variation,  along with a lot more organic material, good soil will develop as a result of nurturing the soil life and keeping the soil hydrated.

Yes, if too much clay is added and allowed to dry out so it can solidify, plants will die. But few plants like soil so porous and sandy that it's usually devoid of water and life.

I think a balance is necessary.

-CK