Hugelkultur with hay/straw is a well-known strategy. I can't offer any particular guidance, but at least you can research it. I'd think you'd need at least 6-8 inches of soil on top. If you have some fresh manure, throw that in with the hay. Note that the bed will sink substantially as the hay decomposes.

LOL! Had to look up that word - never heard it! Glad to know it should work. I figured that at the end of the season I'd roto-till the top soil into the hay underneath if the hay has decomposed enough. If not I'll just add soil from the hot compost as it becomes available. Thanks!

The hay decomposition will be largely anaerobic and slow. So it may not be done by the end of the season. Before you rototill deeply, you might poke it a bit and see who's still down there.

The only thing you want to avoid is seeds in hey, if it's just the straw your cool if not your weeding forever. 1/3 straw / compost / top soil should work really well especially once the soil structure is established, should be like a sponge.

I think any hay seeds that are 6-8 inches underground aren't going to result in any weeds.

I disagree but to each their own.

Dave gives such good advice. Check with a local independent garden center. As for your hay, I recently saw a picture of a beautiful high tunnel garden, in Kansas I think, that was mulched with hay over cardboard. It was beautiful -- not a weed in sight.

I'm so used to doing a hot compost that I completely forgot about the seeds from the hay. I do have plenty of straw so I'll just use that to be sure - I do NOT want to deal with any more weeds than I have to. There is a local source of bulk growing mix but they charge $28 per ton and to fill all the grow boxes would require about 18 yards of soil (24 tons). I'd rather not spend the money if I don't need to. I have about 15 bales of straw that will probably cut the amount of soil needed by a third so I'll just use that.

Steve, you mentioned using 1/3 straw, 1/3 compost and 1/3 topsoil. Any reason I couldn't mix the topsoil and compost together?

Thanks to each of you for your help!

NonE at all

Are we serious, that we're worried about germinating weeds from seeds 6-8 inches deep? Never seen anything like that. A weed that can pull that off deserves to thrive! 2-3 inches, I can buy. FWIW, summer pasture grasses are seeded at a depth of 1/2 inch, and that's what we're talking about. Winter wheat needs more protection, and is usually seeded at 2 inch depth. I think coleoptile lengths max out at about 4-5 inches.

Well..seeds down 6-8 inches probably will not germinate BUT when you rototill later that will bring the seeds up closer to the surface.

We till in our amendments late winter then no more tilling. Weeding is done with a stirrup hoe to help prevent bringing up more weed seeds. This works great for us. I hate a weedy garden! I LOVE my stirrup hoe! Every week to 10 days I run it through the garden. It doesn't take long in our 60' X 80' garden and 10' X 24' raised bed. I also use it in some of my flower beds.

I think you'd be better off using the straw instead of the hay for your purposes.

Hope everyone has a great growing season!

Kathy

Let's back up. When you robotill at the end of the season, those seeds will be germinated and dead, if not composted. Yep, that's what happens. If they are going to germinate at all, they will have done so underground. Grass seed doesn't sit around in soil for years at a time. Burial under 6-8 inches of soil won't stop anyone from germinating. It'll stop germinating seedlings from surviving.

Before someone beats me to it, I should add that yes, there are certain varieties of plants that CAN emerge from great depth. Navajo corn seemed to be able to emerge from these depths quite handily, as it was adapted to germinate in tough desert conditions where surface moisture was almost non-existent. Those seeds are a lot bigger than pasture grass seeds, so the seeds have extra oomph. BTW, that experiment has been tried with modern corn, and it doesn't work at all.

I basically agree with Dan about the weeds but then I wouldn't use either hay or straw in my greenhouse beds. It will create a water table if nothing else and I think you will really regret it down the line.

But then I'd likely have a stroke when I got my first power and water bills for running a GH in Las Vegas anyway. So in the long run it wouldn't matter to me. ;-)

Dave

Digdirt, tell me more about why I would regret using straw, please. I'm not sure I understand. Would the straw not allow water to drain? Thanks!

Pending more info from Digdirt, I've decided to remove the hay and go with the straw. I have plenty of both and don't want to take a chance with any weeds that might survive when it comes time to rototill the straw into the soil. Thank you very much for all your input!!

The primary problem is they both mat down, hay faster than straw. So not only does your soil level fall off quickly but the matted straw becomes a tight, almost water repellent "woven rug" in bottom of the box until it finally rots.

Secondary problem is while straw (a pure carbon) is decomposing, since it is buried, it binds up nitrogen in the soil, uses up the available nitrogen for its composition process.

Your beds are 18" deep right? But you really only need 12" so I think you'd better off just filling them to the 12" depth with good soil rather than using either the hay or straw. Then fill them the rest of the way over the years as finances allow and compost becomes available. If you use the straw they are going to fall to that level anyway as the straw decomposes.

Just some thoughts to consider.

Dave

One can presume that any hugelkultur strategy will result in nitrogen being tied up by decomposition of the carbon, whether it's straw or tree trunks. But I thought the general idea was that by burying the decomposing material deeply, most of the soil growing layers are not nitrogen deprived. That's where hugekultur has an advantage over plain old in situ composting. Is that not correct?

Again, the hay, if buried under 6-8 inches of soil, will NOT have any seeds that will survive eventual rototilling to the surface. Just won't happen. Those grass seeds are soaking wet down there, and they will try to germinate pretty much immediately and not find any sun. I presume that rototilling won't happen until the end of the season. Right?

Digdirt, I guess since my plan was to put the straw down as squares taken directly from the bale, without spreading it out or loosening it up, I would already have the woven rug. Perhaps that would lessen the the "soil fall." Doesn't eliminate the nitrogen problem though. Thank you for explaining that to me - very helpful.

Thanks Dan. It would be nice to be able to just leave the hay there and put soil on top of it.. I wonder if I could alleviate the nitrogen deprivation problem through fertilization. My watering system is set up to deliver fertilizers with the water.