Before planting it is a good idea to find your USDA Zone info to figure out 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.

In Zone 4a you can estimate when you can plant bok choi by looking at the USDA zone info.

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 more sensitive plants.

The earliest that you can plant bok choi in Zone 4a 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. Any later than that and your bok choi may not have a chance to grow to maturity. If you are starting your bok choi indoors then you might be able to get away with starting them a little bit earlier.

Last Frost Date

On average the last frost when the weather gets warmer is on May 15 in Zone 4a. You should expect an average low temperature of -30°F in the coldest months of winter.

Since the USDA zone info for Zone 4a 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 Zone 4a it frosts late in the year after May 15 be ready to protect your bok choi if you have one of those late frosts.

USDA Zone Info for Zone 4a

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°F

This means that on a really cold year, the coldest it will get is -30°F. On most years you should be prepared to experience lows near -25°F.

Plants to Grow in Zone 4a

You may be interested in your other planting guides for Zone 4a.