Weeds should be controlled either by hand weeding or mulching . The addition of organic matter over the plastic reduces heat absorption and masks the artificial appearance of black plastic. Mulching materials should not come in contact with plant stems. The high moisture environment created by mulch increases the chances of stem rot which can result in plant death. This condition is not due to a nitrogen deficiency and can not be corrected by the addition of fertilizer.
Annual flowers require more maintenance than most other landscape plants.
However, their brilliant colors add an atmosphere of warmth and life to a landscape which more than justifies the additional maintenance.