I live in Ontario, Canada. Zone 4b. I've been looking into these two methodologies of no-till gardening and my concern with the deep hay mulching (Ruth Stout) is slugs. Which has led me towards using compost as a mulch (Charles Dowding). The soon to be garden plot (for use in spring 2018) is completely surrounded by tall grasses and 'weeds'. I've hacked away and mowed the area that will be used and will be layering on top of it to choke out the grasses and prepare the area.
My question is about using compost as a mulch, I had never heard of this before, thinking of compost only as a soild additive. Are weed seeds blown in from the top not a major concern? wouldn't it be a perfect spot for grass seed to germinate? (which my garden plot will be surrounded by).
Basically anything that anyone can tell me about compost as a mulch would be of great interest to me.
Weed seeds blowing in will germinate almost anywhere if conditions are right for them e.g think of roads, gutters etc. So mulching alone won't ever entirely solve this issue however it will reduce the bank of seeds available as opposed to the alternative method of disturbing and turning the soil.
If you want to help prevent some of the seeds coming in you can always build up with methods like hugelculture. Also keeping the area well stocked with plants during the growing season means they are usually outcompeted.
For me the downside of using the compost for mulch is the amount needed to do a large area so I now use it on the plants that the slugs like and use woodier mulches for most other plants.
Compost is bio-active therefor it makes a wonderful soil amendment, in no-till methodology it is spread around the plants as a mulch at a 3-4 inch thickness.
Most compost has been "Hot" composted and this heating helps destroy any weed seeds as well as any pathogenic organisms, thus reducing the expected "weed" numbers.
As Henry stated, weed seeds will blow in but we are trying to prevent those seeds already in the soil from having the opportunity to sprout, the fresh blow in is impossible to fully prevent.
Many people like to mulch an entire bed and this does take a lot of compost material, the better method for compost mulching is to mulch around each plant thus using less compost per bed than if you covered the whole area.
You can always come back with a different mulching material to fill in the blank space that doesn't have plants.