When you know the planting zones of your area, you can make smart container plant choices for your apartment garden. Use the hardiness map (click here for a larger version) by locating where you live and matching the color with the chart to the left of the average annual extreme minimum temperature in that area.
The color tells you what planting zone you live in. When researching plants to grow in your apartment container garden, use this information to know if the plant will survive throughout the winter outdoors or if you will need to bring the plant indoors while it is still cold outside during the winter.
Once you know your planting zone, then what? Well, gardeners who live in zone 6, for example, can keep plants that are hardy to planting zone 6, meaning that plants hardy to zone 6 will survive the winter in the minimum temperatures of planting zones 6, 5, 4 and so on. But container gardeners living in zone 6 may choose to only grow container plants hardy to zone 5 and not zone 6. Why? Potted plants are less insulated than plants that have their roots in the ground soil, so potted plants may freeze quicker and not do as well during the winter. Apartment gardeners who live in planting zone 6 may want to play it safe and only keep container plants outdoors that are hardy to zone 5, zone 4, zone 3 and so on. Any other potted plants can be overwintered indoors and grown under grow lights.
Keep in mind that the expected minimum temperature of each of the planting zones is not the same every year, so use the hardiness zones as guides and don’t take them too seriously. And for other factors, some potted plants may just not make it through the winter.
Hardiness zone maps can be a little difficult to read. If you live in a very populous city, read "What's My Hardiness Zone?" to see the planting zones of the 20 most populated cities in the United States.