What you are doing is growing a green manure crop and if you are satisfied with the time it will take to build up the amount of organic matter in the soil what you are doing is oay. It would be faster to add compost.

kimmq is kimmsr

as Kim says, it is just a cover crop. Choose vigorous, fast, deep rooted plants. you don't specify a zone, but if you need suggestions post your area.

The main disadvantage I see to your plan is time scale. It'll take a LONG TIME to improve your soil substantially by simply cover cropping. Many seasons. In fact, I wouldn't just add compost, but remove and dispose of a lot of the sand. Was this a real garden bed once? If so, how did it end up with so much sand?

To the extent that you are making major changes in this bed, I'd point yourself in the right direction and get some soil analysis done. You're not even fully aware about what you're trying to fix.

Yes, your cover crop won't be able to produce any of the plant-usable nitrogen that you need, but the nitrogen-fixing soil bacteria that should eventually take up residence there certainly will. They do magically make their own from nitrogen that is not already in the dirt. Cyanobacteria need moist soils to survive well, but are found in just about every soil ecosystem.

It seems to me that the choice between these 2 options will come down to an intersection between work, money, and time. If you want it 'garden-ready' very quickly, then the compost option is the way to go. That choice costs some money and work.

The other choice will be cheaper, but you'll have less work up front, and it will take time.

Thanks for the feedback, everyone!

> What you are doing is growing a green manure crop

I absolutely agree. I'm just trying to accelerate the process, from seasons to weeks.

> Choose vigorous, fast, deep rooted plants.

I've been planting cowpea, primarily. It has deep taproots as you recommend, and the seeds are large and contain 25% protein which will add significant nitrogen and other nutrients to the soil. I'm also trying wheat because it looks nice like a lawn grass when crowded, and it's also high in protein, though the seeds are small.

> The flaw in your plan is that these plants will be unable to leave behind any minerals or nitrogen that was not already in the dirt

I'm using a ridiculously large number of big seeds which are rich in protein. I believe that the amount of nitrogen, etc added from the seeds alone would be significant.

> The main disadvantage I see to your plan is time scale. It'll take a LONG TIME to improve your soil substantially by simply cover cropping.

I hope to achieve very fast results with the deliberate crowding of the seedlings. The top portion of the soil could be saturated with little roots within 2 weeks, creating lots of channels for water infiltration. It'll probably take much longer for the roots to rot to the point where they'll help the soil to hold more water and nutrients, though.

> How deep? How far do you have to dig before you get to a different material?

I've not dug deep enough to get to a different material, but it's more than 10cm deep.

> you have no earthworms is you have compacted sharp sand.

I thought so initially, but since I started watering the soil, I've been seeing earthworm casts at the edges of the area, where some weeds have also started springing up.

> Was this a real garden bed once? If so, how did it end up with so much sand?

The owners gave up on growing things there and just wanted it to look 'neat' with no weeds.

A couple of years ago, we did cover cropping with buckwheat. It was cut back before it went to seed, so we had control over it, with a new crop planted after the first one was tilled in. We got 3 crops in a short growing season, and much better soil. Admittedly our problem was the opposite - heavy clayey soil - but it worked wonders.

Without knowing where you are, there is a fair amount of guessing involved, but I'd definitely go for a nitrogen fixing crop. You don't want it to go to seed unless you don't mind/can control it as a weed. Whatever you do, it isn't the seeds that provide the soil improvement but the plant mass.

Johnny's Seeds in Maine has a little chart about cover crops. We just picked things from the chart.

I'm using a ridiculously large number of big seeds which are rich in
protein. I believe that the amount of nitrogen, etc added from the seeds
alone would be significant.

Why not save time and money and till a lot of alfalfa pellets into the soil?

I've not dug deep enough to get to a different material, but it's more than 10cm deep.

Four inches? That's not very deep.

well, it is something, cowpeas are indeed productive, both as crop and as manure, and once the bacteria get hold of debris this winter, more nitrogen will be added. Rome was not built in a day. but check your soil for K, P and other minerals. Sandy soils tend to be poor.

to answer Lazy's suggestion of alfalfa pellets, the difference between wheat and pellets is mycorrhizal development.

"The top portion of the soil could be saturated with little roots within 2 weeks"

Very very little roots. You could have huge improvement in the top two or three millimeters of your soil. I suspect you need more than that.

You say you could just get a load of compost and dump it on the garden. So do it! That would improve your soil rapidly. Sure, do a cover crop on top of that if it makes you feel better.

Again nitrogen is not an issue. Don't fixate on it. Slow breakdown of the compost will add nitrogen naturally, and as I said, once the soil biome gets cranking, nitrogen fixing bacteria will populate.

I'm really not sure I understand what's driving you to focus on cover cropping if you have these other options. The method you're choosing is guaranteed to take longer than any other method.

I planted cowpeas in 6 small areas of the sandy garden. The seeds were poured into each area such that they were touching each other on all sides, then covered and watered. They sprung up quickly, displaying their first true leaves within 3 days and shading the areas completely. Since then, not much has changed above ground. I'll dig up some of the roots tomorrow to find out what's going on down there.

> you say you could just get a load of compost and dump it on the garden.

Actually, what I can get easily is manure, not compost. Poultry manure. Large quantities of smelly stuff.

> I'm not really sure I understand what's driving you to focus on cover cropping.

Curiousity. Also, it seems like a very elegant and "natural" way to inject organic matter into soil.

I cut down most of the cowpea seedlings today, 7 days after their emergence. They had completely shaded the soil. Used the leaves and stems to mulch the areas that they were planted in. The stumps left behind, being bent and too thick, made the soil surface look ugly, alas. Root penetration was quite low, as expected in 9 days.

I am currently testing corn, the grass with the largest seeds. The seedlings won't shade or fertilize the soil as well as cowpea, but their thin, straight stems will leave nicer stumps behind. The leaves will be easy to 'mow' regularly too.