Hello Permies!

I'd like to ask some questions about wood chips mulching:

After having watched the Back to Eden movie, it was already February, I wanted to cover my garden soil with mulch. It was laying naked all winter, so I went for wood chips. I put a 10cm (4inches?) thick layer. When it was the time to sow the first carrots and beets I found myself wondering about the following:
It's fresh (=dry, not yet decomposed) woodchips. So I removed the chips in that row and sowed on top of the soil and added just a thin layer chips back just to cover the seeds and protect them from birds. I suppose I need to make sure the area is kept quite moist there, right? Then the seeds will sprout in the soil and will be able to grow quick and easily through the mulch which I will graduately cover the row back up with...?

Still I am leaft with more basic questions about wood chips mulch and how to handle it:

1. As wood chips mulch is supposed to hold weeds back from growing through it, how are the little seedlings, the young vegetable plants that have been sown underneath the mulch, supposed to grow through the mulch then? Mulch doesn't discrimminate, right?
2. Often you read about removing mulch in spring so that the sun can warm up the soil. Sounds logic to me! But so does: In the forrests the mulch isn't removed even in spring. Are there any benefits of having the mulch NOT removed in spring?
3. There is a Youtube video that tells about the necessity to put manure, fresh compost from the pile or other organic material on top of the wood chips in order to creat compost tea when it rains so that the whole mulch system will fill with nutrients that slowly make their way down to the soil which is gradually fertilized. I saw that Paul (Back to Eden movie) does it with his chicken manure/compost, aswell. Wouldn't this mean that this mulch system would grow weeds like crazy?

Hope you guys can clear this up for me. Thanks!
Kerstin

A lot depends on the quality of the soil before you put the mulch on. If it was very good garden soil then what you described is all you have to do. If you want to warm the soil where you are planting you can rake the chips back for your row and cover it with clear plastic which will sprout the weed seeds then cook them on sunny days. If the soil is poor amend it with compost before you plant the row. Only the row or hill needs the compost for the first year. As the system works over the years eventually the soil is good everywhere and you just plant where the path was last yer and let the organisms replenish what you have harvested.

Hans has given some good advice.

Mulching removes light from the soil surface and retains moisture in the soil beneath it, it also helps reduce soil erosion. It is the removal of light that keeps the weed seeds from sprouting, 10 cm of mulch is thick enough to do this for most weed seeds.

In answer to your first question;
When planting, you pull back the mulch, sow the seeds, wait for them to sprout before starting to replace the mulch.
you do not want mulch over the seeds you plant, once they are up you can add back the mulch as they grow, this keeps them healthy and able to grow with out weeds competing for nutrients and moisture.

In answer to your second question;
Removal of mulch to allow soil warming can be done, you can also simply use a black cover to gather heat to warm the soil without needing to pull the mulch back.

In answer to the third question;
Top dressing with compost or composted manure can be done directly on top of the mulch, or it can be placed on the exposed soil to be covered with the mulch as the plants grow. Either way works well.
Remember, weeds need light to grow, the primary function of mulch is that it removes light from the soil.

The benefit of composted materials on top of the wood chip mulch is that as the rain leaches the nutrients through the mulch and into the soil,
it is also starting the decomposition of the mulch by feeding the micro organisms so they can break down the mulch fibers into more nutrients for the soil beneath.

The benefit of composted materials directly on the soil is that all the nutrients leach into the soil without being filtered by mulch. It also allows you to use a trowel to work a bit of into the soil surface as you are planting your seeds.

The method I use is; At the end of the growing season, lay down a compost made of mushroom compost/composted manure/chopped wheat straw, broad fork the bed so the compost can infiltrate the soil. Plant winter cover crop, heavily seed the beds so they will have a thick green cover for the winter. In late Feb. to March chop and drop the cover crop, wait one week then broad fork the beds. April is planting time, plant seeds and put in started seedlings, around seedlings lay down 1cm of mulch, when seeds sprout and reach 2cm height lay down .5cm of mulch. As plants grow add mulch slowly till it is 10cm to 15 cm thick, depending on type of plant. Root veggies get less mulch, strawberries get a mulch of wheat straw that is 10 cm thick to keep the berries from ground rot, squash get a mulch of wheat straw 12 cm thick, things like cucumber, gourds, tomatoes, peppers and corn get up to 15 cm of mulch mixed with finished compost. All melons are grown on trellis with hanging nets for the fruits so the vines can be mulched and top dressed with composted manure/mushroom compost.

Wow, thank you very much for your great and detailed answer, Bryant! I have gotten really a good impression from this how to work with mulch and compost. So in general I got the idea how to plant seedlings into mulch wholes and so on. What you explained made sense to me and I thought of it nearly the same way.

But I still have a question left:
E.g.: After one year, when the wood chips mulch had been toplayered with compost and winter cover crop clippings and stuff, all the chips have been soaked with nutriens because of past rain falls... Wouldn't that mean that the surface of that mulch, being rich in nutrients and LIGHT, would be coverd with weeds like crazy? Isn't it's function to shaden out the soil lost after the mulch layer itself has become a nice place to settle down for weeds? Isn't that actually the fact for all kinds of mulch layers? That is what I'm still left wondering about - this function of the mulch to hold back weeds...

The only answer I can think about is when you look to garden centers and stores, they sell special soils to sow into. They are less nutricious because the young seedlings won't be overfeed as if they were in compost-rich soils. So does this work for weeds coming up in compost-rich mulch then, too?
But then again I think of the Back to Eden movie, how Paul was directly sowing into the decomposed mulch layer.... And, when sowing into the soil in mulch wholes, isn't this soil compost-rich, too?

I don't really get it, it seems contradicting to me somehow...

Mulch, to be effective in weed reduction needs to be around 4" thick (if a ground cover ie: landscape cloth, old sheet or something like them is laid down first then mulch can be 3" thick),
with this in mind and the fact that when we talk about compost we mean fully finished compost, there should be no live weed seeds in finished compost.

The leaching effect is what moves nutrients from one layer to another along with capillary action.
If you have a proper thickness of mulch covered with a layer of finished compost, there really should be no light reaching the underlying soil, it is this lack of light that makes mulch effective at weed control.

Those special seed sprouting soils are a mix of composted materials with additions of fertilizer. We just bought four bags of the stuff for our straw bale gardens, the reason we did this is they grow our tomatoes, peppers and some squashes which we put in as transplants.
These transplants do best when the planting holes are large and some "soil" is added around the root ball, most commercial potting soils have slow release fertilizer included in the mix, which helps the bales break down further which is what we want.
Since this year is the first year for these bales, my wife wanted to add some of this stuff, and even though I can do the same thing more permaculture, I also know when to let her have her way. Next year she will go along with my coffee ground/manure/leafmold compost because we also have some bales that are mine to play with. She is already noticing that mine are growing the same items, just as well as her bales are growing them. Sometimes the best way to educate is to demonstrate

To most gardeners, especially those used to doing things the "commercialized" way, things we do seem to be counter intuitive, but what we mostly do is use things Mother Earth uses for the same things that companies make with artificial fertilizers and such.

Most compost is not extreme when it comes to nutrient content, rather it is balanced, the inputs are what determine the finished product. If you put in more greens than browns, you can end up with a higher N content but it still won't be way out of balance due to the way thing deteriorate in nature.
Decomposition in nature allows N to leach into the soil with every rainfall, along with other nutrients, so when the decomposition is complete, most of the nutrients are already in the layers beneath. Just because something is "compost rich" doesn't mean the nutrients are out of balance, actually the opposite is more likely to be true.

You putting wood chips on a non sprouted plant will prevent it from growing.

I took a Soil Science class some years ago. They explained that the whole purpose of working the soil before planting, was to ensure that the seed, would have a good coating of soil to go around it, and deliver moisture to the seed so it could sprout... As someone said above, it would be good to sprout your seeds, then crowd the mulch back around them.

One thing you may unfortunately notice with mulch, is that you provide habitat for critters, such as voles, who might not ordinarily live in your garden. Voles are herbivores, to my understanding, moles are carnivores. The voles nearly wiped out our asparagus one year, and I suspect might be busy again out there. They are hungry little buggars!

I hope this helps. Welcome and good luck! Best, TM

Hey everyone,

thanks for your replies!!! I really appreciate your input!

Unfortunately, my questions have not really been answered yet. So let me try again.

Take a wood chips mulch layer that is some inches thick, and then on top of it take a topcover of (ready) compost mulch that will gradually fertilize the wood chips and soil below it after rainfall and so on. The mulch layers on top of the soil are so thick that no daylight can penetrate through it. You know, just the standard mulch - compost layer sytem.
My question is: Even if weeds (and of course also beneficial seeds) are hold back from sprouting from underneath the mulch - this is what mulch is doing - what about the weeds that could spout from on top of the mulch layer? Sprouting in the compost layer? It is fertile soil, it has access to daylight, it holds moisture, so why aren't the weeds coming up like crazy there? To me this would seem logical! But I dont hear people complaining about having mulched and composted their soils and have gotten enourmes weeds problems.

Bryant: I read on German websites and webshops that sell sprouting soils that these soils are less fertile than normal garden soil! Just the other way round! And there are also instructions on other DIY websites, how to make those soils and it's instructed hat you take plain garden soil from the garden center (not additionally fertilized) or your own garden soil and mix it with sand so that you'll create "poor" soil for your seeds to sprout in! I am suprised to read that yours is so very different then...?

So in fact we are now talking about two topics here:
1. Why don't masses of weeds on top of a well fertilized mulch system, with plenty of access to daylight, come up like crazy?
2. Is it perhaps because the over fertilized "sprouting soil" - meaning here the top layer of this well fertilized mulch system - is too strong for the young seedlings? If this is the case, is that why sprouting soils need to be weaker, poorer than normal garden soil? What makes sprouting soil so different and better for sprouts and seedlings than normal garden soil anyway?

Hope I could express myself better this time... If not, please ask what needs to be clearified.

Hi Kerstin, really excellent detailed information here! My simple answer to your question, based on my experience of using tons of wood chips for about 4 years now:

- yes you will get weeds growing "on" your mulch after two or three seasons of new seeds dropping onto the surface of the mulch, if you leave it undisturbed. In the section of my yard where I sheet mulched with thick cardboard and 6" of woodchips in order to kill Bermuda grass, I had complete cessation of weeds and grass initially. By the third year I needed to pull annual weeds growing in the decomposing mulch so I just add a fresh layer of chips, about 3" thick.

- in the vegetable garden, I use the fresh woodchips as mulch which eventually becomes part of the soil as it decomposes - so you do need to keep adding a thin layer of fresh woodchips every year for annual weed suppression. I have mounded beds so I spread about 4" thick on the sides and a little thinner on top around the vegetable plants. When the mulch is fresh you will have virtually no sprouting of new weed seeds.

I have heard of folks putting down cardboard and then covering it with soil.
But I don't hear of people putting down mulch then covering it with dirt.


But back to your original question.
Mulch blocks sunlight.
Soil covered mulch causes an increase in fungi which uses up all of the available mineral thus making the soil poor.
The top layer of mulch normally get super dry

So I think the answer to your question is there is not a super abundance of weeds on to because it is difficult for the seeds to get there. Dandelions and fire weed can float in on the wind and cleavers get packed it by you and your pets. The weeds that come up in super abundance drop there seeds close the the plant. The reason the come up in super abundance is you spread them around when you cultivate. Cultivation prepares a seed bed for weeds and sows the seeds at the same time.
The goal is to only cultivate enough space for the seed or transplant you want to grow there. Now if you want a nice bed of lamb's quarters and the seed is in the soil cultivate the spot and then weed out the undesirables.

Bryant: I read on German websites and webshops that sell sprouting soils that these soils are less fertile than normal garden soil! Just the other way round! And there are also instructions on other DIY websites, how to make those soils and it's instructed hat you take plain garden soil from the garden center (not additionally fertilized) or your own garden soil and mix it with sand so that you'll create "poor" soil for your seeds to sprout in! I am suprised to read that yours is so very different then...?

So in fact we are now talking about two topics here:
1. Why don't masses of weeds on top of a well fertilized mulch system, with plenty of access to daylight, come up like crazy?
2. Is it perhaps because the over fertilized "sprouting soil" - meaning here the top layer of this well fertilized mulch system - is too strong for the young seedlings? If this is the case, is that why sprouting soils need to be weaker, poorer than normal garden soil? What makes sprouting soil so different and better for sprouts and seedlings than normal garden soil anyway?

Sprouting soils can be just about anything, for an example, when I worked at Peto Seed Farm, we used blotter paper and incubators to sprout many of our trial cross seeds then planted the sprouted seeds in a compost/sand/vermiculite mix in 4"pots. Obviously blotter paper is void of plant nutrients, so yes you can sprout seeds in nutrient devoid mediums.
The reason most use nutrient poor "sprouting soils" is two fold, first, yes they don't need many nutrients to get going, everything a sprout needs is in the seed. However, if you were to let that newly sprouted seed stay in that medium for more than three weeks, you would have starving plants.
The nutrient poor sprouting mix also keeps the plants from bolting and falling over dead. If you are monitoring your sprouts at least once a day, it is an easy thing to add more dirt around the stem, as the stem grows, this will have the function of more roots being formed and it also gives the baby plant support.
In my own case, I make my own using a formula that I developed in 1970 for Peto Seeds. Since I check my plants twice daily when sprouting, use small size cube trays which are transplanted one week after sprouting to 4 or 6 inch pots, and I leave 2" of free space for support filling. In my opinion, each person should do what works best for them. I have been working in the agriculture field for over 50 years now, I still experiment and keep good notes on the results.

Now for your number one weed question. Most compost if it is "finished", meaning it has heated up to around 160 f., any weed seeds (all but the sturdiest desert plants, perhaps) are dead. This means there are no weed seed able to sprout in that compost. So if you use said compost as a top dressing on mulch, you won't see weed seeds sprouting simply because any that are there are dead seed and decomposing or are already decomposed.
If you do see weeds growing on top of the mulch, they are most likely wind blown volunteers that found a happy place through their travels on the wind.

High nutrient levels are dangerous for newly sprouted plants, over nutrition can cause bolting, (plant shoots up faster than the cells can harden to support the plant) this caused fall over which tends to kill the new sprout. Sprouting soil doesn't need a lot of nutrients since most are going to be transplanted fairly soon after sprouting to larger containers. Sprouting mediums can be just about anything (including shredded newspaper) as long as they hold moisture and are able to support the base of the newly sprouted plant. What type of plant is being sprouted, thin stem or thick, usually has a bearing on which medium is best for sprouting the seed.