Weeds need sunlight to grow. When wood mulch decomposes or is spread too thin it allows weeds to flourish because they receive sunlight. Over-mulching can deprive your plants of oxygen. Rubber mulch when applied correctly will prevent sunlight from making its way to the weed seed but still allow oxygen to your plants. It's recommended to also apply a weed barrier landscape fabric as an extra layer of protection against weeds.
Mulch Type Tag