Good summary, Bill. Excellent info!

Dave

Here Here! Couldn't have said it better myself Bill...

Blutranes

I'm sorry to add a fly to the ointment, but if Bill's "When a green colored green dries out, it is still a green despite what color it may turn." was correct, everything we compost would be a green. As grass clippings dry out & turn brown, much of the N is volatilized and they end up a brown.

Al

As grass clippings dry out & turn brown, much of the N is volatilized and they end up a brown.

Oft debated it's true, but the consensus is the reverse. Dried grass is still more of a green than it is a brown and will usually act as such in a compost pile.

Dave

I agree with Al to a point. It is not that simple but magazine writers have gone the extra mile in trying to make it so.

Rather than thinking of green and brown, carbon and nitrogen, I think in terms of protein and carbohydrate. Grass is a "green" as long as it has at least 5% protein content (95% carbohydrate). As soon as the protein is decomposed by the microbes, then the grass becomes something else that has never been explained. But then the microbes that decomposed the grass become full of protein and are 'green.' Green colored grass might lose all its protein in a day or two when the microbes living on it start to decompose the protein.

When the compost pile is finished cooking, ALL of the nutrients in the pile have been consumed by microbes. Even the nutrition inside the microbes has been consumed by other microbes. All the nutritious waste products from the microbes have been consumed by other microbes. All the non-nutritious waste materials have not been consumed and they are left in the pile. With 100,000 species of microbes in a typical pile, what you are left with at the end of the process is a pile of non-nutritious (to animals) waste material. If there were any nutritious material left, there would be more microbes in there decomposing them until there is absolutely zero nutrition left. Any microbes remaining in the pile have gone dormant because there is no more food. Fortunately they are easily awakened with food and water. Also fortunately the stuff in the pile happens to be nutritious to plants or is easily converted to nutrition for plants by other microbes in the soil. Also fortunately the compost retains the ability to absorb ammonia gas.

If you leave a pile of grass alone it will stink in a day or two. In that case Al is right about the nitrogen volatilizing and blowing away. That means that ammonia smell, the stink, is the nitrogen blowing away. However, if you compost the grass with dry leaves or other heavy "browns," they absorb ammonia gas and retain it. They do the same for carbohydrate gasses like methane.

I'm by no means a compost expert, but aren't you assuming that the grass is turning brown while in a compost pile? Why would straw always be considered a brown, yet dead, dried brown grass a green? Based on that wouldn't other dead leaves, once green and high in carbohydrates and proteins always be a green? What makes dead grass different than other greens gone brown in its ability to absorb ammonia? Wasn't the ammonia already locked in pile to begin with?

Al

Al, much of it depends on whether the leaves turned brown on the plant or off. If they were green when they were on the plant and turned brown later, they should still be considered greens. If they turned brown on the plant, they're considered browns.

When I can't get my mind around something, I tend to doubt. If one of you can point me to a reliable online source that confirms what you said, I'll read up on it & quit buggin'.

I reason that the relationship (ratio) of ligninous materials: cellulose is pretty important in the separation between browns and greens. Those materials that were high in lignin were browns and those with a disproportionate ratio of cellulose:lignin were greens. That is how I would rationalize that brown, dead grass might still be considered a green, but you're saying that if it was green when it was separated from the plant it's always a green? When it was separated doesn't do much to change the cellulose:lignin structure, so that would make my cellulose:lignin thinking wrong. I know it's not, because the presence of lignin and suberin in pine bark is what makes it break down so slowly in container soils - making it an excellent base for them. Hmmmm ...

Al

I oversimplified a bit. Depending on how something is dried, it could lose N to the atmosphere, but if you take green grass and dry it out, it will still be a green. If you let your lawn die and cut it, it's going to be a brown. If you're just drying something, what you're doing is removing the water, so the ratio of Carbon to nitrogen stays the same. But you're never just drying something, and nitrogen is more volatile and more likely to gas off than carbon, so in some cases, something could lose enough nitrogen to go from green to brown, but usually, if something would be considered a green when it's wet, it's still a green once it dries.

Perhaps if you look at it from the POV of C/N ratios.

Some Common C/N Ratios (range)

sawdust 150-200
fall leaves from oak, maple 40-60
peatmoss 50
fresh grass clippings 15
sun-dried grass clippings 20
straw 50-150
hay from legumes 15
raw garbage 25
cow manure 30
fresh garden debris 20

Grass clippings, even when dried, still have a C/N ratio of only 20, substantially lower than that of fall leaves or straw. So while an argument could be made that dried grass clippings has more carbon than fresh grass clippings, it still falls on the less-than-30 C/N ratio or the "green" side of the line.

Straw and/or sawdust with their high C/N ratios are often considered the "perfect" browns. Conversely, fresh grass clippings, often called the "perfect" greens. I know from personal experience with it that sun-dried filed hay that is over a year old can still kick start a compost pile within 24-48 hours. ;)

In the link below, if you click on the internal link called Appendix A, it gives you a detailed C/N ratio list.

Dave

Here is a link that might be useful: Cornell C/N Ratios

As vegetable waste dries it could loose some of the Nitrogen value it had, depending on how it is handled. Grass, which is similar to hay, as it is cured does not necessarily loose its high N levels although it could. Just stand next to a pile of grass clippings gasing off N to the atmosphere and smell the strong ammonia odor. However, grass left in thin layers cures without loosing N, just like hay would. So if you stored your vegetable waste in a way that if could gas off N, and you smelled ammonia which is an indication of N loss, it might end up a "brown", a substance with a high C:N ratio, expressed as 50:1.

Here is a link that might be useful: C:N ratios

...aren't you assuming that the grass is turning brown while in a compost pile?

Grass does not turn brown while it is in the pile. It turns to compost.

Why would straw always be considered a brown, yet dead, dried brown grass a green?

Because straw does not have any protein in it. Grass does. Straw is an agricultural by-product, the dry stalk of a cereal plant, after the grain or seed has been removed. Before the grass forms a seed head, the protein "lives" in the grass blades and stalks. When it forms the seed, all the protein is concentrated in the seed. Wheat is an example. There is an old saying about separating the wheat from the chaff. Straw is chaff.

Based on that wouldn't other dead leaves, once green and high in carbohydrates and proteins always be a green?

Yes...until they decompose into compost. Alafalfa, clover, and vetch are three examples of plants with leaves that hold on to protein. The concentration of protein in a plant is a characteristic of grass, nuts, seeds, and beans as well as some legumes. If you are thinking of tree leaves, only mimosa and acacia trees have much protein. Most garden variety trees have flowers. Those flowers become fertilized by pollen and develop into to seeds or fruit with seeds in them. The leaves don't have that much in the way of protein.

What makes dead grass different than other greens gone brown in its ability to absorb ammonia?

The presumption that greens turn brown is incorrect. Greens decompose into compost, and browns decompose into compost. Protein sources are the cause of ammonia gas. If grass is mowed and remains moist, it starts to decompose. If it is in a pile, you can smell the ammonia. If it is not in a pile, it dries out. The microbes that decompose it into ammonia need moisture to do that job. So if the grass is allowed to dry out, it may discolor as the leaf dies, but it does not lose that much nitrogen. Browns absorb ammonia as does the finished compost itself.

Wasn't the ammonia already locked in pile to begin with?

Yes if the pile had adequate "browns" (dry tree leaves are great for this). The ammonia is the result of the decomposition of protein. If your pile never had any protein in it, then there will be no ammonia to absorb. If your pile is composed of nothing but protein sources (like grass), then the ammonia will escape and the pile will smell. If the pile already had carbohydrate materials (browns), then it would have absorbed any ammonia from prior decomposition of protein.

Right now leaves on my mulberry tree are quite green in color. A textbook says the C:N ratio is 25:1. Are they "green" using the insiders argot here?

In a couple of months my mulberry leaves will be quite brown in color. Will they "brown" or "green"?