I could easily kill a cactus in under a week, so if I ever want a garden I'll need to plant everything in Wonder Soil. Wonder Soil is fertilizer-rich dehydrated peat which expands when you add water. One 14 oz. container is equivalent to 10 lbs. of regular soil.  Polymers in the soil time-release water so if you're a once a week (or month)  waterer like I am, your plants may still survive.