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.

The USDA zone info for Diamond Bar should be used to determine when you can plant welsh onion.

Planting Calendar for Welsh onion

Frost tolerance for welsh onion:	Tolerant of a very small amount of frost.
When to plant:	Up to 3 weeks before last frost.

Welsh onion do ok in moderate cold which means that you can get them planted just a bit earlier than other frost tender plants.

The earliest that you can plant welsh onion in Diamond Bar is February. However, you really should wait until March if you don't want to take any chances.

The last month that you can plant welsh onion and expect a good harvest is probably September. If you wait any later than that and your welsh onion may not have a chance to fully mature. Starting your welsh onion indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

On average the last frost has passed is on January 31 in Diamond Bar. It might get as low as 30°F during the coldest months of winter.

Keep in mind that USDA zone info for Diamond Bar is an average and the actual date of last frost is different every year. Half of the time in Diamond Bar it frosts late in the year after January 31 so be sure to be ready to cover your welsh onion in the event of a late frost.

USDA Zone Info for Diamond Bar

Here is the info for USDA Zone 10a.

Average Date of Last Frost (spring)	January 31
Average Date of First Frost (fall)	December 15
Lowest Expected Low	30°F
Highest Expected Low	35°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 35°F.

Plants to Grow in Diamond Bar

You may be interested in your other planting guides for Diamond Bar.