One of the best tools that you have as gardeners to help us figure out your gardening schedule is the USDA zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

In Portsmouth you can estimate when it's the best time to plant astilbe by checking out the USDA zone info.

Planting Calendar for Astilbe

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

Astilbe are barely cold tolerant which tells us that you can start planting them slightly earlier than more sensitive plants.

The earliest that you can plant astilbe in Portsmouth 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 astilbe and expect a good harvest is probably August. If you wait any later than that and your astilbe may not have a chance to fully mature. You can get started a few weeks earlier by starting your astilbe indoors.

Last Frost Date

In Portsmouth the average date of last frost happens on April 15. It might get as low as -5°F during the coldest months of winter.

Remember that the actual date of last frost is an average because it is based on the USDA zone info for Portsmouth and it will vary from year to year. Half of the time in Portsmouth last frost occurs after April 15 so make sure that you are prepared to protect your astilbe if you have one of those late frosts.

USDA Zone Info for Portsmouth

Here is the info for USDA Zone 6b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-5°F
Highest Expected Low	0°F

This means that on a really cold year, the coldest it will get is -5°F. On most years you should be prepared to experience lows near 0°F.

Plants to Grow in Portsmouth

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