In the landscape beds, mulches can really play an important role in limiting weed seed germination by keeping the seeds in the dark. Once the mulch breaks down naturally and sunlight can once again get to the soil, weed seeds are triggered and they are back. Once mulch is applied and settles, it should be two to three inches deep and kept away from the base of trees and crown of shrubs, perennials and annual flowers. The better way to manage landscape bed weeds is to apply the mulch to a clean bed to start with. Perennial weeds having a good taproot will still be able to regrow through the mulch. Spot treatments with systemic properties will, when applied to the new emerging foliage, move into the roots and take care of the weed for good.
If the look of open bare soil is what is preferred, frequent very light hoeing or soil disturbance is needed to control any emerging weed seedlings before they establish any kind of a root system. If the soil is constantly kept loose after every rain when weed seeds are germinating you can exhaust the seed bank in the upper quarter inch of soil and the beds end up being relatively weed free. Wind can always bring in new weed seeds, so no one is off the hook for the season.
Where you have beds of the same kind of plants like the annual flowers, a pre-emergence seed control product can be effective. There are still some rules that need to be followed to get good results. Typically new plantings will need to be left to grow for a couple of weeks to settle the soil around the transplants roots or if sown from seed, enough time has to pass before the product can be applied. As with the landscape beds, the soil should be weed free before making any application. If weed seeds have germinated into those tiny weed plants, pre-emergence products will not control them. These products work by either preventing seed germination all together or killing the emerging root radical at the point of germination. Another rule that normally applies is that once applied, do not disturb the soil or you break the barrier and weed seeds can once again germinate and show up.
The last and least liked way to manage the weeds is to pull them while they are young and have a minimal root system. Pulling a Lambsquater weed that is only two to three inches tall is easy, let it get a foot or more in height and it becomes a two handed effort and then hope it just does not break off and re-sprout off of what is left.