Iris bulbs do great when they are planted in the fall. This gives them plenty of time to grow strong roots so that they can bloom the next summer. But how late is too late to plant them?
If the ground has already frozen where you live, it’s too late to plant iris bulbs. It’s best to plant your bulbs at least six weeks before the first hard freeze (when temperatures drop below 28 degrees Fahrenheit for several nights in a row) so that they can establish a root system before winter hits. In most climates, September is the latest iris bulbs should be planted.
Let’s talk more about why timing is important when planting iris bulbs.
When Is It Too Late To Plant Iris Bulbs?
If you plant your irises immediately before a hard freeze, there’s a good chance they won’t survive the winter. While bulbs are very hardy, they still need time to get established before the cold weather hits. This is especially true in climates where temperatures drop below zero degrees Fahrenheit.
The exact cutoff date for planting iris bulbs depends on your location and specific climate, but in most places, irises should be planted by the end of September. This is a good way to make sure your iris bulbs have a few weeks to get established before overwintering.
To calculate a more exact time for planting your iris bulbs, take a look at your USDA plant hardiness zone. Find the average first frost date for your zone. The first hard freeze usually takes place several weeks after the first frost, so you’ll want to plant your iris bulbs at least three weeks before the first frost date.
For example, in zone four, the average first frost date is anywhere from September 21st to October 7th. To make sure irises have enough time to establish, they should be planted by September 1st in this zone.
Can I Wait Until Spring To Plant My Iris Bulbs?
If it’s too late to plant iris bulbs in your zone, you might be wondering if you can wait until spring to plant them. The good news is that yes, you can plant your iris bulbs in the spring once the ground has thawed.
However, it’s important to keep in mind that you shouldn’t expect blooms the first summer if your bulbs were planted in the spring. The irises will spend their first season establishing a healthy root system and should bloom the next summer. Occasionally, they’ll be able to bloom in their first season, but it’s not very common.
Iris bulbs are low-maintenance and easy to grow, but it’s important to plant them at the right time. By making sure they have at least six weeks in the ground before a hard freeze, the bulbs will be able to establish a strong root system that can survive even the most brutal winters. Alternatively, you can plant your bulbs in the spring once the ground thaws.