Hello world, this is Chris, here to deliver a daily dose of permaculture existential questions.
There are many things that seem simple on paper in permaculture. Mulching is one of them. The theory goes: you throw a copious layer of dried plant material (straw, shredded bracken, pea straw, grass clippings, alfalfa straw, coconut husks, woodchips, etc.) on your garden bed, and you will have solved many of the most preoccupying problems of the average gardener: you prevent water loss through evaporation, nutrient loss and erosion from rain, wind and heat, inhibit weed growth, and boost microbial and invertebrate life in the soil. And if you want an even longer lasting mulching regime, you can go for sheet mulching and spread a layer of cardboard or newspaper, then a layer of compost or aged manure, and then a layer of brown plant material, and this should be even better at banishing drought and weeds and boosting fertility in your garden.
Wouldn't it be nice if it were that simple! But there are some pitfalls to know about. The first is that a thick layer of mulch means that the soil is going to take longer to warm up in the spring, so you may want to rake your mulch to one side when the sun is shining to help the ground warm up. Of course that's tricky if there are lots of perennials in the bed. This might be a reason why our peas and broad beans didn't come up for the most part. One sunny, circa 15-20 degrees Celsius day, wondering if they were on their way, I stuck a finger in the ground, and sure enough it was really cold right under the sheet mulch (that I had installed when the ground was still cold). I hear that cold ground is a common reason for peas not coming up (these guys have a solution).
Next, I wonder how you can reconcile planting seeds directly in the ground and sheet mulching. Planting perennials in mulch or sheet mulch is fine, but can seeds push through mulch? Probably not, since that would put in question the weed suppressing properties of mulch. So should you wait until your seeds have come up, and then put mulch between the plants? I have tried several different tactics here. I have sheet mulched, then made gaps in the top layer of dry plant material, and planted seeds in the layer of soil+composted horse manure above the cardboard. This has worked for lettuces, I guess their roots made it through the cardboard below. I've also tried planting seeds in bare ground, and then mulching in between. It becomes impossible to sheet mulch in this case, but spreading some brown much material among the plants is easy enough. Is it enough to suppress weeds and do all the other magical things mulch does? We shall see...
One thing I have noticed is that a thin layer of mulch thrown on top of direct sown clover seeds made a huge difference. I just threw the clover seeds on the ground without burying them, which meant that when the sun shone and the earth dried out, the seeds would sit there and refuse obstinately to germinate. Areas on which I had half-heartedly thrown a thin layer of mulch, however, where full of tiny clover seedlings. So, among all my questionings of the value and appropriate use of mulch, this is my one shining success story! In fact, I have taken to throwing a thin layer of mulch material on the seedling beds, and do believe this to be better than bare ground, while not inhibiting seedling growth.
So, mulch can delay soil warming in the spring, and has varying impacts on seedling. But it gets even more technical if you look into it. Some mulches compact down in the rain, forming an impervious mat that prevents water infiltration, while mulches can absorb all the water from light rainfalls, and then evaporate it back into the atmosphere, leaving the ground below dry. This means that mulching is not necessarily a water saver, but can actually be a water waster! I have noticed this when I watered the mulched beds copiously, and then stuck a finger in them only to find that below the soaked, spongy mulch, the ground was bone dry.
In addition, uncomposted, green mulches, especially uncomposted wood chips, contain phytotoxins and hormones that inhibit plant growth. They also tie up nitrogen, and can starve the plants. Doesn't sound too great... Anyone out there going to take a stand for green mulching?
Lastly, there is the question of how deep to plant perennials in mulch, especially sheet mulch. Should the top of the root ball be level with the cardboard, the compost, or the straw/clippings? If the plants are too deep, the mulch around the stem can favour fungal diseases and crown rot, while planting them too high will make their root ball more likely to dry out.
So, I guess this is what happens when you take your head out of your books and try things out for real. You realize things aren't that simple! At least, that's what I'm going through right now, and I often feel confused. What would Bill Mollison do?!
Our mulching has been done with dead bracken we pulled up in fields, and shredded with a weed wacker. Apparently it's high in potassium, making it especially good for things like potatoes. On the other hand, it grinds up pretty fine, which makes it more likely to form a dense mat with less air flow. Maybe we should try mulching with unshredded bracken to see if that would make a more fluffy, porous mulch.
In permaculture, you live and learn. Nothing can replace direct experience and experimentation. Hopefully I can figure out the intricacies of mulching, and I'll be sure to keep you posted if the universe teaches me anything more on the topic.
For an interesting discussion on the impacts of different mulch types, you can read this. Also for another practical account of mulching strategies and lots of great advice, check out this post on Patrick's blog.
PS: So I think I was a bit down on mulch when I wrote this. I must say that we've just had a dry period of a few weeks, which just ended, and I really noticed the difference between sheet mulched beds and bare beds. We barely watered the perennial cabbage/leeks/walking onions bed, which is sheet mulched, whereas the greens and broadcast sown beds, which aren't, required daily watering. Also, I can now vouch for the weed suppressing properties of mulch. So In short, sheet mulching is awesome, especially for planting seedlings later in the spring once the earth is warm. In other cases, you just have to give it some thought. But I like giving thought to what I do in the garden, so that isn't a problem, is it?
