Before planting it is a good idea to find your USDA Zone info to estimate your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

A common way of determining when you can plant bok choi is to check out the USDA zone info for Billings.

Planting Calendar for Bok Choi

Frost tolerance for bok choi:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

Since bok choi do well in moderate cold you can plant them a little bit earlier in the year than other frost tender plants.

The earliest that you can plant bok choi in Billings is March. However, you really should wait until April if you don't want to take any chances.

The last month that you can plant bok choi and expect a good harvest is probably August. You probably don't want to wait any later than that or else your bok choi may not have a chance to really do well. If you are starting your bok choi indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

On average the last frost is on May 15 in Billings. In the coldest months of winter you can expect an average low temperature of -25°F.

Since the USDA zone info for Billings may not be accurate from year to year the actual date of last frost changes from year to year. Since half of the time in Billings there is a last frost after May 15 be ready to cover your bok choi in the event of one of those late frosts.

USDA Zone Info for Billings

Here is the info for USDA Zone 4b.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-25°F
Highest Expected Low	-20°F

This means that on a really cold year, the coldest it will get is -25°F. On most years you should be prepared to experience lows near -20°F.

Plants to Grow in Billings

You may be interested in your other planting guides for Billings.