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.

The first opportunity to plant zinnia in Riverside should be estimated by looking at the USDA zone info.

Planting Calendar for Zinnia

Frost tolerance for zinnia:	Not tolerant of frost.
When to plant:	After the last frost.

You should not plant zinnia until after all chance of frost has passed because they require warm weather.

The earliest that you can plant zinnia in Riverside 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 zinnia and expect a good harvest is probably September. If you wait any later than that and your zinnia may not have a chance to really do well. You can get started a couple of weeks earlier by starting your zinnia indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on February 15 in Riverside. In the coldest months of winter you can expect an average low temperature of 25°F.

Remember that the actual date of last frost may not be accurate from year to year because it is based on the USDA zone info for Riverside and it will vary from year to year. Half of the time in Riverside last frost occurs after February 15 so make sure that you are prepared to cover your zinnia in the event of one of those late frosts.

USDA Zone Info for Riverside

Here is the info for USDA Zone 9b.

Average Date of Last Frost (spring)	February 15
Average Date of First Frost (fall)	December 15
Lowest Expected Low	25°F
Highest Expected Low	30°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 30°F.

Plants to Grow in Riverside

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