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

One way of getting a good idea when you can plant tithonia is to look at the USDA zone info for Mercer Island.

Planting Calendar for Tithonia

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

You really shouldn't plant tithonia until after all chance of frost has passed because they require warm weather.

The earliest that you can plant tithonia in Mercer Island is April. However, you really should wait until May if you don't want to take any chances.

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

Last Frost Date

The average date of last frost is March 15 in Mercer Island. In the coldest months of winter you should expect an average low temperature of 15°F.

Always keep in mind that USDA zone info for Mercer Island is just an average and the actual date of last frost can change quite a bit from year to year. Half of the time in Mercer Island there is a last frost after March 15 so make sure that you are prepared to protect your tithonia in the event of one of those late frosts.

USDA Zone Info for Mercer Island

Here is the info for USDA Zone 8b.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	15°F
Highest Expected Low	20°F

This means that on a really cold year, the coldest it will get is 15°F. On most years you should be prepared to experience lows near 20°F.

Plants to Grow in Mercer Island

You may be interested in your other planting guides for Mercer Island.