What should I fill my newly made planters with? They are five foot long by two foot wide by one foot high (eg: just earth or a mixture of new topsoil and compost).
What Is the Best to Fill Planters With?
It depends on what plants you plan on using. If annuals will be used, I suggest using equal parts potting soil and top soil. Using a quality (commercial), peat-lite potting soil with sterilized top soil makes a mix that is easy to use, yet heavy enough to hold moisture. You can definitely use compost instead of the potting soil. Sterile top soil will reduce weeds and pathogens.
If the planters are concrete, I line them with a thick trash liner. This keeps the soil from being to alkaline from the lime in concrete. Just be sure to poke drain holes in the liner.
If you use plants with a 'drinking problem', like petunias, consider using one of the moisture retaining polymers. Also, if you use plants that need lots of nutrition, add a time release fertilizer to supplement water soluble plant food.