Whole or shredded…leaves are good mulch

Autumn means falling leaves. Depending on your point of view, you might see them as a nuisance, or as a treasure. Perhaps they are both. Many gardeners dislike using whole leaves as mulch because they tend to mat and are slow to break down into soil.
Take a careful look at your garden situations. Do you want a long-lasting mulch for trees and shrubs? Leaves will serve. They will smother weeds in neglected corners and improve the ground in compacted shaded areas under trees where grass won't grow.
Leaves may take a year to break down. This slowness is an advantage. I pile at least a ½ foot, preferably more, of loose dry shredded leaves under shrubs and around small trees, they mat down quickly, and the appearance is acceptable.
Leaf mulch will rejuvenate depleted areas under tree shade where nothing, not even weeds, will grow. The accumulated leaf mold has improved the soil so much that soon I expect to put in some woodland plants there.
Leaf mulches also control weeds. This allows moisture to seep through to shrub and tree roots, yet smothers most weeds. A few minutes spent laying such a mulch in fall or early spring can keep the area neat and weed free all year, at no cost.
Leaves do tend to make the soil more acid. On the pH scale they register on the acid side. Some such as oak leaves are more acidic than others. Over a long period, a heavy leaf mulch could increase soil acidity, benefiting acid-loving shrubs such as azaleas and rhododendrons, and most woodland plants. On the other hand, plants preferring neutral to alkaline conditions, such as most vegetables, might be harmed unless lime is also added. An occasional soil test will tell you what to do.
My own experience with using leaf mulches on beds has shown them to be beneficial in both winter and summer. In spring, they can be a disadvantage, as they delay the warming of the soil. Whole leaves will mat down and hinder or cripple the emergence of spring growth, so I much prefer using chopped leaves for mulching. Chopped leaves don't mat, they stay put, and they break down into leaf mold much faster than whole leaves.
You can chop your own leaves with a shredder, or by running a lawn mower over them a few times. Chopped leaves are excellent erosion preventers on slopes and they insulate soil to reduce alternate freezing and thawing in winter. To prevent diseases from overwintering under a leaf mulch, clean the garden in autumn after first frosts have blackened tender vegetation. Leave ground bare until hard frosts arrive; then apply two inches of chopped leaves around but not over your perennials.
In spring you may find that the mulch has pretty much become integrated into the garden soil.