Use this planting calendar to find the best times of the year to grow fruits, vegetables, herbs, flowers, and other popular plants in Portsmouth, IA, based on the USDA Hardiness Zone 5b.
On this page:
Portsmouth, IA Frost Dates & Growing Season
Last Spring Frost Date for Portsmouth, IA
The average last frost date in spring for Portsmouth is April 30th. For gardeners planting sensitive crops like tomatoes, peppers, and basil, it is generally recommended to wait until May 14th before moving plants outdoors. Waiting these extra few weeks significantly reduces the risk of a late freeze damaging young transplants.
First Fall Frost Date for Portsmouth, IA
The average first frost date in fall for Portsmouth is October 6th. This date marks the approximate end of the growing season for tender plants. Gardeners should plan to harvest frost-sensitive vegetables or provide heavy protection (such as row covers) before this date to avoid crop loss.
Growing Season Length in Portsmouth, IA
Based on historical frost data, the estimated growing season length in Portsmouth is approximately 159 days. This duration determines which vegetable varieties have enough time to reach maturity before the winter cold sets in. Short-season varieties are recommended for crops that require a longer warm period.
Please note: These dates are climatological averages. Actual weather conditions vary by year. Always check the local 10-day forecast before planting.
Portsmouth, IA Planting Calendar
This weekly planting calendar displays the ideal windows for starting seeds, transplanting, and harvesting your plants.
Portsmouth, IA Monthly Planting Recommendations
February
In February, recommended activities include starting Lavender seeds indoors (from February 19th to March 5th), starting Snapdragon seeds indoors (from February 19th to March 5th), and starting Begonia seeds indoors (from February 19th to March 5th).
March
In March, recommended activities include starting Cabbage seeds indoors (from March 5th to March 19th), starting Broccoli seeds indoors (from March 5th to March 19th), and starting Marigold seeds indoors (from March 19th to April 2nd).
April
In April, recommended activities include direct sowing Dill (from April 16th to April 30th), direct sowing Alyssum (from April 16th to April 30th), and direct sowing Calendula (from April 16th to April 30th).
May
In May, recommended activities include direct sowing Runner Bean (from May 7th to May 21st), direct sowing Black Bean (from May 14th to May 28th), and direct sowing Mung Bean (from May 14th to May 28th).