Why haven’t my irises bloomed?

Melanie Mathieson
Gardening Guru

Many fellow gardeners have contacted me, this summer, with concerns about their bearded irises. Many gardeners may find that their bearded irises did not bloom this year or if they did bloom they seemed to have smaller and less flowers than usual. This has happened to many gardeners with multiple varieties of bearded irises including many of my own irises of which I have over 30 varieties.

Assuming that the plants of which you claimed have not bloomed are healthy and are mature (planted for more than one season) the reason for the lack of blooms this year is not the hot and dry weather that we have been experiencing but the conditions that we experienced last summer. The leaves and flowers of bearded irises are developed from a tuber called a corm. The leaves emerge first, then blossoms will follow after the leaves have developed about 75%. Most of the varieties of bearded irises hardy to our zone will flower between mid-May and late June. Once the flower has blossomed and died back the leaves will grow to their full height and then work very hard, the rest of the season, to replenish the corm with much needed energy that is used to develop the leaves and flowers for the next growing season. It is very important to make sure that you do not cut back the leaves on the bearded irises until the fall, once they are completely brown. If you remember the weather of last summer, it was quite cool and rainy most of the season, with very little sunshine. Because of these conditions many varieties of irises in the district were unable to rebuild their energy stores in these less than favourable conditions, therefore unable to produce flowers this season. The good news is that the hot dry weather we are experiencing this season, will help the irises to recover and rebuild their energy stores, as bearded irises love these hot and dry conditions, unlike many other perennials. Next year may very possibly be a banner year for flowers in both abundance and size.
Here are a few more tips to ensure that you are caring for your bearded irises the proper way so you can produce healthy and hardy plants.
1. Bearded irises grow best in a full sun location. This means an eastern to southern exposure. Not only do they require sun, for most of the day, directly on their leaves but also need sun exposure on their corm in order to remain healthy and produce enough energy in their corm to produce flowers and leaves for the next season. When planting bearded irises make sure you place the corm in the soil so the roots and bottom 2/3 of the corm are planted securely in the soil. The top 1/3 of the corm should be located above the surface of the soil so it receives direct sunlight. Always plant the bearded irises of any variety in this manner regardless whether you buy an iris already planted in a pot that is completely buried in the soil (this is an incorrect planting but some nurseries plant their irises deep in the pot so they don’t fall out of the pot once the leaves grow). Planting the corms below the surface of the soil is one of the most common mistakes made by gardeners, but is the very easy to rectify. Also make sure that if you are adding mulch to your garden that you do not cover the corms with mulch as the corms must remain exposed to the sun. If you have planted your irises incorrectly, once the hot dry weather has passed you can dig them up and replant them properly before mid-September. Doing so buy mid-September will give the plants a few weeks before freeze up to reestablish themselves firmly in the ground so the frost doesn’t heave them in the winter.
2. Never add fertilizer to your flowers when the weather conditions are hot and dry. Wait until these weather conditions pass and then fertilize. Once we get a few days of steady rain and the temperature drops to a normal level, it will be the right time to add a fertilizer to your irises. Remember to use a fertilizer with a high middle number (high in phosphorus - to produce roots and flowers). I like to add a slow-release granular fertilizer to the flowerbed in mid- to late August to help out the irises in the final days of the season.
3. Bearded irises need to be divided every four to five years or sooner if the corms become very crowded. Once the drought conditions pass you can dig the corms up, break apart the healthy corms from the old dried out parent corm (and throw the dried corms away) then replant the healthy corms using the methods stated above. Keep in mind that the irises that you have divided may not bloom the next season but will bloom usually by the second season.
Of course many gardeners plant bearded irises because they love their unique and exceptionally showy flowers. I think that the only negative characteristic of the bearded iris is that the flowers don’t last long enough, so it can be very disappointing when the plant doesn’t produce any flowers at all in a season. Patience can be a gardener’s best virtue so I guarantee that if you follow the tips stated in this column you will be rewarded next season with the best display of bearded irises ever.