Find the size of your containers to determine the size of the bag you want to buy.
For example, a 20-quart bag fills two 12-inch standard clay pots, or you can fill one 14-inch basket and still have enough to fill half of another 14-inch basket. To follow this example, find the pot sizes in the column on the left, and then follow the line to the right to the shaded boxes.
|Size of bag and approximate number of pots that it fills|
|Pot type & size||Approximate soil volume of pot*(dry quarts*)||10-qt bag||20-qt bag||32-qt bag||40-qt bag||64-qt bag|
|STANDARD CLAY POTS|
|8 ¼ inch||3.6||3||5½||9||11||18|
|10 ¼ inch||6.9||1½||3||4½||6||9|
|STRAWBERRY JAR 5 gallon||14||¾||1½||2¼||3||4½|
|21 ¾ inch||31.2||¼||½||1||1¼||2|
This isn’t perfect, but it beats a wild guess.
When you buy potting soil, are you just guessing at how much you need? We hope this table has given you a way to figure how much to buy. However, these figures are approximate. Here’s why:
There are very few standards regarding container sizes and volumes. To make it even more confusing, containers that do list volume typically measure using liquid quarts. Of course, potting soil is not a liquid, so the bags contain dry quarts, which are about 1 1/8 liquid quarts. None of this is really important to your success. We’re just explaining so that you will understand why the numbers on this table are approximate.
Nor do these figures account for any packing down of the soil (the taller the container, the greater the compression). Compression can cause you to need 15% to 20% more soil. On the flip side, the soil that comes with your transplants (the roots) will add volume.
Do take notes about your own pots if you have containers that you use over and over again. That is the only way to know exactly how much to buy.
Store leftover soil in a dry place, perhaps in a clean plastic tub or garbage can, until next time.
Adapted from soil volume tables from Conrad Fafard, Inc., makers of commercial and home garden potting mixes.