As balcony container gardeners, we buy some plant containers and bags of potting soil from our local garden center, and then we grow our favorite container plants. Simple. But when we purchase bags of dirt, what are we getting exactly, and why can’t we just dig up some dirt from the ground and use that instead?
First of all, unless you mix your own garden soil, do not use dirt from the ground in your plant containers. Ground dirt is not porous enough to allow good drainage in our plant containers. So you go to the local garden shop for some healthier and better-draining soil and pick up a bag that says “potting soil” on it.
So what is “potting soil,” exactly? Well, potting soil has no actual “soil” in it. It is actually a soil-less mix, including peat moss, ground pine bark, vermiculite, perlite and added nutrients (often with slow-release fertilizers). And what’s even more confusing is that there seems to be a “soil” for every type of container plant: vegetable mixes, rose flower mix, bulb mixes, etc. The good news here is that for most of the plants in your container garden, you will be able to use just regular “potting soil.” Plants like succulents and cacti need extra sand, and orchid flowers need to be planted in peat.
Good potting soil is well-draining porous material made of particles between one-sixteenth and a quarter of an inch in size. Too-small particles will create a dense garden soil that does not drain properly, and anything too large will not retain enough water. When you water container plants, the water should penetrate the soil quickly, and excess water should drain out quickly. The soil should be able to absorb water quickly and hold up to two times its own weight in water. Ideal potting soil doesn’t shrink or swell when watered or when dried. If it pulls away from the plant container when dry, you probably not have a high-quality potting soil.
The pH of your potting mix is important, but you shouldn’t have to worry about this until you’ve used the same potting soil for more than a few years. The pH of the mix will change due to fertilizers and the type of water used to water the plants in your balcony garden (your tap water may be hard or alkaline). Container plants can tolerate soil pH between 5 and 8.5, and they will begin having nutrient deficiencies outside of those ranges. After using the same potting soil mix for several years, purchase a cheap pH test kit from your local garden shop (you can even ask if your garden center tests soil pH), and see if you have an inappropriate pH. You can use additives to alter your potting soil’s pH if needed.
The best part about purchasing potting soil for the balcony garden is that it is free from weeds, garden pests and pesticides. It is not unheard of to have worm eggs or other hitchhikers in a purchased garden soil, but your odds are much lower of obtaining pests from bagged potting soil than dirt from someone else’s garden. Although it may sound quite complicated, purchasing potting soil is can be as simple as buying a bag with the words “potting soil” on it!