Yard Clean Ups:
If you are not having problems with diseases (examples; powdery mildew, rust on leaves) or insect problems such as Iris borer it is better to wait to clean up your garden till early spring (March) when the snow first melts off the garden. The various plant stems will catch leaves and snow, insulating your plants from the frequent freeze and thaw cycles or early and late winter. These rapid swings in temperature are what most often kill garden plants by heaving them out of the ground when it freezes and, sinking them back in when it thaws. This up and down movement damages many of the plants fine feeder roots making it difficult for the plant to survive.
It is best to chop up the garden debris into small pieces and spread them over the garden to recycle the nutrients that are stored in the old stems and leaves. Do this by spreading the garden debris out in a 2 to 4 inch layer over the lawn and driving/pushing your lawn mower back and forth over the debris to chop it into pieces. Then you can spread it over the garden once again. This gets the debris to lie down and look nicer and helps speed decomposition.
There are two approaches to how often to mulch. Some people spread 1 inch of mulch every year to keep nice brown color of bark much looking fresh. This also is a less daunting task to spread since it is a smaller amount of mulch.
The second approach is to mulch every other year with 2 inches of mulch which reduces the number of times you have to mulch but doubles the amount of work when you do mulch.
Mushrooms in the mulch: With any of the mulches don't be surprised if you see mushrooms or slime molds growing on your mulch for a short period of time. These fungus are needed to knit the mulch material into a mat that will suppress the weed seedlings. The fungus also initially decomposes the material to make the nutrients accessible for plants.
Types of Mulch:
There are many different types of mulch and it is better for the soil if you vary the types of mulch you use to end up with a rounded balance of nutrients in the soil.
Shredded Bark Mulch:
The most common type of mulch used is shredded hardwood bark that comes from the lumber mills. It is an attractive mulch that does a good job of forming a mat to suppress weed seedlings.
Stained Shredded Wood Mulch:
You can now buy shredded wood mulch that comes from old pallets and construction waste. They grind up these boards and then dye them with various colors. It is a good reuse of material that would otherwise go to the landfill, the dyes are unlikely to be organics and they give the mulch a uniform color which looks unnatural. Because of this I don't generally use this product unless a customer asks for it.
Leaf mulches both suppress weeds and quickly improve the soil because they break down faster than the wood based mulches. When using leaves it is more attractive if you chop up the leaves and then spread them. Do this by spreading the garden debris out in a 2 to 4 inch layer over the lawn and driving/push your lawn mower back and forth over the debris to chop it into pieces. Then you can spread it over the garden once again. If you can it is good to spread a mixture of oak and other leaves that break down quickly like maple, ash honey locust, and hackberry. The quickly decaying leaves can form a dense mat in wet springs that can be bad for the perennials if it is a thick layer. Shredding helps alleviate this, but it is best to mix in oak leaves (also shredded if you are shredding) which are rigid and decompose slowly. This creates air spaces in the mulch and keeps if from getting too dense in wet years.
Coco Bean Mulch:
Coco Bean mulch is very attractive, and depending on the person either smells wonderful or awful. It has a rich brown color and a nicer even texture but it comes from countries where chemical spray restrictions are looser and tends to have a chemical residue on it. If used it should be mixed with rice hulls because in wet years it will not get a chance to dry out and can become very slimy.
Wheat or Oat Straw makes an effective mulch if spread on thickly but it can bury smaller plants and is generally better in vegetable gardens where the plants can get above the straw. You will also get wheat and oat seedlings which look like grass growing in the mulch (which some people find unsightly. These are annuals and if you stop them from going to seed (by pulling out or mowing if in the lawn area) they will be gone the next year.
Marsh hay is very similar to straw but tends to have fewer seeds that can grow in the average garden setting.
You should not use regular hay to mulch because it is riddled with seeds and will introduce a whole host of weeds into your garden.