Using Mulch

[BobT]

A thin layer of mulch only an inch deep will prevent plants from growing yet I can plant my seeds a couple inches deep and they grow just fine.  This may seem like a silly question but how does this work? Can anyone explain this?

Thanks.  

[roony]

I use straw as mulch in my tomatoes. It doesn't stop all the weeds from coming but it sure slows them down a bunch. I suppose part of it is because mulch is not the same as soil so weeds have a harder time busting through it. Of course plastic mulch is better for weed protection but it has other disadvantages.  Hope this helps a little.

 

[delcecchi]

A thin layer of mulch only an inch deep will prevent plants from growing yet I can plant my seeds a couple inches deep and they grow just fine.  This may seem like a silly question but how does this work? Can anyone explain this?

Thanks.  

Simple.  an inch of mulch like straw or chips won't prevent weeds, although it will retain moisture etc.  It takes more like a foot of straw. 

Less than an inch of newspaper, cardboard, plastic, etc will stop weeds.

[Early Riser]

Most of the time mulch is used in-between established desirable plants, and in the rows between beds. 

Mulch is typically laid down early in the season where you don't want undesirable plants to grow, and then again after your desirable species are growing in order to smother out weeds that would otherwise arise. 

Personally I typically mulch in my main vegetable garden at home with composted leaves and grass clippings from the previous year. This is done in the springtime and early summer. Now that my beds are thick with full growth plants, there is a lush canopy of "living mulch" so that I really have no weeds anywhere in the garden to speak of. 

In the fall I mulch heavily in all my paths between beds with chopped up leaves from neighborhood lawns. I probably go through 20 of the ubiquitous brown bags full of leaves in the fall, and store an additional 20 bags over the winter for use as carbon rich brown material to mix with my grass clippings, coffee grounds from various sources, and our kitchen scraps for making compost through the following garden season.  

I started another garden up at my brother-in-law's cabin near our Hovland homestead this past April by tilling up an area in a large opening in his forest, laying down a 1" layer of composed horse manure from my neighbor's pasture, and covering it all with black plastic mulch. I planted seed potatoes to further break up the ground through slits in the poly. All are now growing, flowering and putting out copious tubers, with virtually no choking weeds. I have used all kinds of organic material for mulch, including newspaper, large rhubarb leaves, weed cuttings prior to going to seed, fresh grass clippings, logs, etc. It all goes into the ground, brings in a lot of worms, and greatly enriches your soil over time.

[BobT]

I can place a 1" thick layer of grass clippings from my lawn between the rows in my garden and weeds will not grow, which means it inhibits the growth of even those seeds that are on the surface.  I can plant seeds up to a 2"-3" deep in soil and then pack it down and they will still find their way to the surface.  How is it that the grass clippings deter growth when soil does not?  That's what I can't understand.

[pushbutton]

One thing that might come into play is the size of seed/variety  Most seeds that you can plant that deep are larger, produce a stronger shoot/sprout, and can push through. Most weed seeds are a lot smaller.Dont think lettuce or carrot seed would push through mulch either. Would also assume non disturbed more hard pack mulched over areas are not going to "grow" as many things as well as the recently cultivated rows that will get more water, light, air.....or whatever is need for more successful or stronger growth.

 

 

[BobT]

It's almost as if the seed is able to distinguish that there is a layer of mulch overhead and won't push through it but if the total amount of soil over the seed was the same depth, it would push through.  

Carrots and radishes and other similar seeds I fully understand.  If you plant them 2" deep they won't grow.  But peas and beans will push through 2" of soil.  I've never tried planting them 1" deep and then adding 1" of grass clippings to see if they would still push through.  Maybe the weeds that are growing are like the radishes and carrots and require shallow planting?  That might explain it I guess.

[Dotch]

Pushbutton has it right. An old weed science rule of thumb is that the smaller the weed seed the shallower it needs to be in order to germinate. Things like woolly cupgrass, cocklebur, velvetleaf and giant ragweed have relatively large seeds so they can come from a fair depth, up to 4" deep for cocklebur given the right conditions. Things like lambsquarters, pigweed, foxtails, etc., have smaller seed so laying mulch or crop residue over the top of them will tend to lower their germination in a given year. Eventually by repeating the process, the weed seed bank is greatly diminished as a result. 

[roony]

I think the weed seed bank around here is FDIC insured. 

 

[pushbutton]

Just remember it is against MN law to give away weed seeds to your neighbors, family, and friends. They must aquired through an approved weed seed library or officially inspected first. 

[Powerstroke]

The difference I'm seeing in your discussion BobT is your comparison of grass clippings to mulch. Grass clippings are actually quite dense and you need a lot of grass to make a 1" blanket of clippings. In the places that I have piled grass clippings before, the grass clippings will kill anything else underneath. I'm not sure if it is too dense, or if it creates too much heat while decomposing or what. 

I would say that grass clippings is not a typical organic mulch. Also, comparing mulch on top of soil to seeds placed below soil is not an apples to apples comparison. Seeds are designed to germinate and seek the surface. Its what they do. Soil is a very light and porous material compared to a layer of decomposing organic matter piled on top of the soil. 

[BobT]

Thanks for the explanations.  It makes sense.  

For what it's worth, I learned a lesson this year.  Using the grass clippings was an experiment I attempted as a way to control weeds and make use of them when I mowed the lawn.  I discovered it isn't necessarily the best thing to do as they created a problem.  I noticed my wife was watering the garden a lot and even after we had received some pretty significant rainfall amounts.  One time I asked her why she was watering the day after it rained over 3".  She said her tomatoes were drought stricken.  When she lifted the layer of grass clippings she found the soil underneath was dry.  Apparently, the grass clippings are dense enough to shed the water off the garden like a roof rather than allowing it to penetrate.

Live and learn I guess.