From helping with soil temperature and moisture regulation to blocking out weeds, mulch is often considered a gardener's best friend. My go-to mulch is natural, organic pine bark (usually mini nuggets, but shredded is also ok) as it's has a good pH level for most plantings. I recommend staying away from dyed mulch. I'm personally not a fan of the artificial colors and am leery of any dyes or chemicals leaching into the soil when they break down. As for timing, there are 3 key times when you should mulch your plantings, so here's a quick rundown.
Early Spring
Early spring is the perfect time to refresh your mulch as much of it has broken down and worked into the soil over the winter. I like to add a layer 1"-2" thick to my planting beds and containers that still have a bit leftover from the previous fall. Go a bit thicker if your old mulch is gone and the soil is totally bare. This acts as a protective barrier that regulates moisture in periods of heavy rain or dry spells, prevents erosion and also helps to prevent unwanted weed seedlings from taking root. I also like the way it brings a tidiness to the beds and containers.
*Adding mulch before the plants have started to leaf out again will be much easier!*
Fall
Putting down mulch in the fall is much like adding a warm, protective blanket to your plantings for the winter ahead. I go a bit thicker with fall mulching, more like 3", which will help insulate the soil and plantings along with continued moisture and erosion control. As mulch breaks down, it also adds structure and beneficial organic matter to the soil in the same way that compost does. Careful not to cover any cutback or spent perennials with the mulch as this could lead to rotting.
Immediately After Planting a New Bed/Container
Newly-planted garden beds and containers need a good mulching right from the start. Disturbed soil is often most conducive to opportunistic weeds as well as erosion and mud splattering during rain, so giving your new plantings a heavy mulch (3") immediately after planting. Be sure to soak thoroughly with a lengthy watering to ensure the new plants get enough to drink right away.