Sheetmulch straw top cover has seeds, what to do????

Aloha all,

I threw together a sheet mulch garden with some extras I had lying around.

I used cardboard on the very bottom to kill suffocate any weed growth, then I threw about 4-6 inches of straws that had seed.

Next layer, I threw 4 inches of heavy duty compost that is really nutritious and was baking for over a year.

Lastly I threw mulch on top but the wood chunks were so big I was scared they would never decompose down so I scraped them off and threw more straw as the top cover.

Well, not even a week later I see tons of what looked like grass and was in awe that my compost would have weed seeds in it. Then I started pulling them up and they were seeds from the straw on the top layer. The straw has tons of seeds in them.

I'm in Hawaii and I have no idea about straw and what it actually is but I got tons of it popping up now from my sheetmulch- no dig- laborless garden. I know now to never use anything with seeds but what can I do about all the future straw?

Do I pull out each seedling as they pop up? Or can I wait till they all get 6-8 inches tall and cut them down to provide more top cover and carbon for the garden? If I cut them without pulling up the seed will the cut blade grow up again? Is there only one generation of seeds or will I forever have straw(cereal grain I think) growing?

I feel horrible because my sister saw mine and I had leftover materials so I made her a raised bed sheet mulch bed exactly the same.

Fellow Permies, what would you do? Thanks.

The compost baked for a year, you say.  Chances are the outer regions of the compost were not cool enough to destroy weed seeds, and some could have blown in while the pile cured.  Compost makes a fine soil amendment, but as a mulch it can promote weed growth.

Straw usually comes from grains.  If you are in Hawaii, I doubt this was imported due to cost, meaning its most likely local.  It could be a local grass.  Sure would be interesting to see what comes up.  What about a small patch intentionally planted with the seeds from this straw? 

Another option is to pull up the grass, mulch again.  While it can offer carbon when you cut and drop, the growth will also rob nitrogen

As far as the wood chips not decomposing, this can be a useful feature-long lasting mulch can save you the labor of remulching.

I regularly use hay as mulch: often considered a no-no because of all the seeds.
All I care about is getting my hands on mulch and I'm more than willing to deal with any germination!
How thick's the mulch? I try and have a pretty decent layer, around 10-15cm. so that seeds touching the soil struggle to get through and those that germinate in the mulch layer are easy to deal with.
I imagine thick mulch would be especially important  in a tropical climate, with the insane speed of decomposition.
Anyway, I just lift the very top layer, uprooting the (usually grass) and lay it back down. I don't want to bring lower layers up, or I'll set off another round of germination.
I try to do it on a hot day when it's not about to rain, as I want the seedlings to fry and not re-establish themselves.
The hay I use is mostly rye and timothy, which don't have creeping stolons. I'd be less relaxed if I thought I was introducing something pernicious.
I'd follow Ken's advice and check out your local species.

The top layer of straw is about 4" thick.

The seedlings are definitely not weeds from the compost but are from the seeds in the straw. I can see the seeds cracked and roots coming out and digging into the compost while the seeds are still on straw.

I called the feed store I originally got the straw from and they told me it was imported. This is all interesting as I've been told grains don't do well in Hawaii.

I think I may take off the top layer and put the wood chip mulch back on, then for the very bottom straw under the compost I'll just cut when I see them pop up.

Thanks for the responses guys. I'm still all ears if anyone else has any input?

See if you find out if it's straw which is the stem, along with a few seeds, of ONE type of grain, or if it's hay, which could be a whole mixture of different grasses along with a nice collection of seeds. 

Straw is usually not much of a problem as all the stuff that grows from it is generally just one type and so long as you cut it or pull it before it seeds the problem goes away.  We regularly have a nice lush growth of wheat from areas we have mulched.  Usually it's pretty easy to pull out as the roots are mostly in the mulch so we just pull it and either throw it on top of the mulch or feed it to one or other of the critters.

Hay is a bit more tricky as you could have a whole load of different weed seeds to contend with.  Maybe try turning the whole top layer of mulch, complete with weeds, upside-down so that the roots dry up.  But do it before any of it goes to seed!

check through near the straw and see if you can find a few seed heads to help identify the grass, possibly even a few ungerminated seeds. around here the straw is either wheat or oats. i always have volunteer grains come up from the mulch and leave them. silly to pull out whats going to grow into food. even if the wheat starts in mid summer, one plant will give me 100 wheat berries easily.

I had this same issue this year. I built some hugle beds, seeded them with vetch, yellow clover , and radish, and then put a thin layer of oat straw over them. I couldn't believe the lush lawn that sprouted up. When the oats got 18" high, I took the string trimmer and cut them down half way so the vetch and clover could get some light. Now, after a month, I'll do it again. Good thing the yellow clover is a biennial. As long as the oats don't get a chance to go to seed, I'll be fine. Next year I'll be inspecting any straw I buy much closer.   

It's all straw of one type. I've attached pics if anyone can recognize what it is. 

You have wheat, barley or rye on your hands. 

hopefully it is an annual type of grass that will dye off and leave a green manure behind, my problem here is I can get things like quackgrass seed in any "brought in" mulches, esp straw or hay or animal manures..and then I'm in a pickle as they ruin my garden..so careful is the word when bringing in anything onto your garden

Aloha guys and thanks for all the replies. I posted before and after pics so everyone can see my little project. I ended up raking off the top layer of straw and just throwing the mulch back on. It seemed easier than worrying about all the germination of the grain.

I hope the bottom layer of straw seeds will not be able to grow because it's too far down under 6+ inches of compost and mulch and it won't be able to set roots in the cardboard anytime soon. If they pop up I'll deal with them when it happens.

As you can see the side of my house has only a small sliver of land. I've got exactly the same depth of land all the way around my home so I have to be really space efficient. Luckily I have State owned land behind my house that no one babysits and I'm planning on planting breadfruit, mountain apple, tangerine, banana; I already planted avocado, orange, & papayas. Dreams of one day having acres but for now I just learn and experiment on what I've got.

Thanks for all the replies guys- I continue to learn so much from all of you.

curious as to why you didn't like the grains growing. it is food after all.

Why I didn't grow the grains..... I did want them growing. I thought it would be a nice supplement to my campaign for self sufficiency but found more reasons not to grow it:

All the resources on Grain growth in Hawaii conclude that it brings nasty fungus problems and they don't do well. Many commercial farms and small gardeners have tried growing for food or feed for cattle & poultry, and none have had a successful harvest.

Felt grain to be a labor intensive food. While it offers carbs you burn more growing it and bringing it to the table. My philosophy is if you can't directly pick it and eat, it's processed and I don't want to mill seeds down and deal with recipes for breadmaking. Breadfruit grows on trees and offers great starch.

Didn't want to share my nutrients/sun and take away from my other vegetables or get in the way.

I did plant a small 2'x2' experiment section of the grain seeds on the other side of my house. Hawaii has 11 of the world's 13 climate zones so I wanted to conduct my own research in my climate zone because I'm not sure if the research was done in the wet or dry, high or low. Some Hawaii climates have great Asian pears and plums, some have great citrus, mountain apple only grows up in the mountains, some soil has so much coral nothing grows. I just am interested to see if I can do it.

Thanks everyone for the comments and questions.

fair enough, but just so you know. you don't have to grow wheat just to make bread or flour like everyone thinks. there are tons of recipes that just cook the wheat like rice would or its added to soups and such whole like barley. meaning you can get a good amount of nutrition from a small patch of grains. sprouted wheat berries are also very nutritious.

Thanks Hubert, I honestly was one of those who thought wheat was only good for bread. I am now more hopeful to see my experiment patch develop so I can cook it like rice.

well you don't cook it just like rice. search for wheat berry recipes on google. youll get thousands of hits. and also sprouted wheat berries too.

I think this is pretty common, at least in my experience. The way plants grow (inconsistent height), and the way straw is harvested it's always going to have some shorter stalks in it with seed heads. It's annoying though. I just pull them up which is very easy as the root system isn't down in the dirt. The issue for me is that I never have deep enough straw down to shade out weeds (can't afford a nice 8" thick layer, alas).

Now, a few years ago I left half a dozen bales out during the winter. The seeds sprouted, grew, died, and I used the straw the following year. I'm pretty happy with that, though there was a bit of mold inside the bales.

Looks like someone didn't thresh their grain very thoroughly. It isn't difficult to kill young wheat, stirring or turning the mulch will do that.

IMO the difference between straw and hay is important, and often misunderstood.

Straw is senescent stalks of the cultivated annual grasses known as cereals. Sensecent means the stalks have transfered most of their minerals and energy to the grain and then died. Straw is high carbon (mostly cellulose), low in minerals, decomposes slowly. It is regarded as a waste product in large commercial monoculture cereal farms. These farms produce nice clean straw with no weeds in it. Sustainable organic cereal farms don't use herbicides so they usually have weeds at the seeding stage in with their straw. They also are often reluctant to give away their straw. They will sell it only if they don't want it for their own uses (such as bedding animals or composting). In composting terms "brown".

Hay is grass (or grasses, herbs etc.) cut when green and full of life and dried. It is rich in minerals, relatively low in carbon. It decomposes fast. Mountain meadows can be cut every year or two with little or no manure or fertiliser, the wild herbs and flowers thrive, but the yields can be pretty low this way. Some hay is grown at higher yields commercially with fertilisers. But IMO buying this kind of hay is effectively buying fertiliser. In composting terms, hay is "green".

Haymaking is skilled labour/energy intensive and takes a lot of land. Hay is not a waste product. The amount of hay needed to permanantly maintain a mulch thick enough to suppress weeds is huge. I tried this method for several years. I estimate that for every square meter of garden you need at least 3-4 square meters of highly productive hay meadow to be devoted entirely to your garden. If the hay is from hay from a nice traditional low input wild flower meadow, probably more area is required. I used fresh cut grass. Hay is dried and has less volume, 3-4 square meters is a very conservative estimate. So vegetable yields from this kind of garden would have to be divided by 4 (at least). Energy (human and/or mechanical) required for the hay also needs to be considered in the equation, and makes this method less attractive.
Weeds did grow up through the hay if the mulch wasn't replenished faster than it decayed. I found 18inches of mulch would kill established grass and weeds, six inches would keep new weed seeds germinating.

I have in the past been given free grass clippings from golf courses and salvaged old spoiled haystacks destined to be burned or landfilled (where I live farmers cut rather more hay than they need, in case of a long winter, store surpluses for a year or two and then dispose of it), so some years there is lots of surplus spoiled hay, other years none. I know someone whose neighbour is cutting masses of nettles and gives them away to use as mulch. But these are exceptional circumstances. Once you embark on a system of permanant mulch, you need a continuous supply of mulch. If you are surrounded by wasteful farmers, overusing fertilisers and throwing away materials they should be returning to their own soil, it's good to use those materials.

IMO the best use for hay is feeding animals in winter. I have seen animals going hungry after all the locally available hay was bought and used to mulch footpaths.

Many gardeners use mulch temporarily in summer, and clear the ground in spring so the soil can warm up. This means they can use mulch when it is available, but aren't dependent on it.

Bill Mollison commented that sheet mulch was expensive, and seemed to view it as a way to establish perennials more than as a way to keep annual vegetables weed free.

I have 50 grow bags, all kinds of vegetables with companion plants. How did I do 2 days of research, settle on Wheatgrass, and not know about the seed problem... such expensive positing soil I'm using, was seed free... good knows how long I'll have to deal with this. A carpet of seedings... a lot of work, tough with companion plants... everything was going so well... never use wheat grass.