Iris plants are distinctive in the garden. Especially around those wet areas where most deep-rooted plants would die of root rot.
With over 300 iris species to choose from, there’s multiple colors to choose that produce gorgeous petals.
Of course, having irises not blooming is just having green stalks poking up from the ground. It’ll give you some decoration, but it’s highly disappointing when you’ve been looking forward to the colorful blooms for months.
The flowers on these are distinctive as they produce six petals shooting out at the top of the plant. Three of the leaves stand upright, while the other three are “fallers” that trail from the seed pod.
There are two types of irises. Bearded and beardless. Bearded irises bloom from spring into early summer. The beardless variety are the later bloomers.
5 Reasons Why Irises Won’t Bloom
1 – They Need Time to Get Established
Irises need time to settle into their new homes. That can take months. It’s estimated that over 60% irises will not bloom in their first year because their rhizomes need to get established in the ground first.
The vast majority of irises are suited to planting in the later part of the summer months, or early fall at the latest.
The longer these are in the ground, the more greenery they can grow. They need that time and protection by late fall from the first of the winter frosts. And, they’ll need protected again from the early spring frosts.
That’s why it’s preferable to get these established in the garden earlier.
For any plant to flower, it needs the leaves for photosynthesis. Sunlight promotes photosynthesis so make sure it gets plenty.
2 – Full Sun Locations Are Needed
Irises are sun loving plants. This is not a type of plant to have under the canopy of a tree where it gets dappled sunlight.
For the iris to bloom, it needs at least six hours full sun every day.
It is a lot and that is because irises use a ton of energy. If you don’t train it to devote that energy into blooming, it simply won’t.
Its natural instinct is to pour all its energy into reproducing because the mother plant rarely reblooms, or at least no more than twice in one year and that’s only if you plant rebloomers.
The bearded iris is the reblooming type that can bloom from early spring, into summer, then burst into a second round of blooming later in the season.
There are subtle differences between getting an iris to bloom for the first time ever, the first time in a new a season and getting an iris to bloom again in the same season. The main difference being that these need to be divided after a couple of years.
3 – Dividing Irises to Prevent Crowding
After two years, irises start to lose their vigor when (or if) they flower. The mother plant only blooms a couple of times at most. The new blooms are on new rhizomes.
Irises pour most of their energy into growing new rhizomes, which are like tiny stems that sit just below the soil surface. They are not roots that store a ton of water.
Because of the fast-growing nature of the rhizomes, and the fact that the rhizomes cluster, irises are terrific plants to absorb lots of water.
On the flip side of that, they can take on too much water. So, only plant them slightly beneath the soil or there’s a BIG risk of stem rot. That will definitely prevent the plant from blooming.
4 – Getting the Planting Depth Right
When you plant irises (or transplant them), only have the rhizomes scratching the surface of the soil. The rhizomes need air circulation and that’s highest at the topsoil. Not buried deep.
An inch is plenty of depth for an iris. Any deeper than two inches in ground soil lacks the airflow they need to breathe.
Given the amount of water these absorb, the rhizomes will rot fast when buried too deep.
If in doubt, plant them higher. At least if they’re planted too shallow, they may not bloom, but they won’t die of rot either. They will if they suffocate from being planted too deep.
5 – Spacing is Pertinent
The spacing is another component that needs to be considered at the planting stage.
Given these are often planted in groupings of multiple iris divisions, they cannot be planted too close together.
Again, it’s the air circulation that gets reduced when rhizomes crowd each other out that become problematic.
To get the spacing right, you need to know what you’re growing.
- Bearded irises, which are the most common type across the US can be planted with one to two feet of spacing between each plant.
- Beardless iris plants need an addition one foot of space – between two and three feet apart.
Caring for Irises
If you’ve just planted irises in the garden this season, it may take them until next season to establish themselves in the ground soil. A lot can be said about patience with gardening. Irises do make you wait.
While you wait, there are other things to take care of to make sure they have the healthiest rhizomes for going into next season.
One of those is mulch and it’s something to be careful with.
Mulch Can Be Good or Bad for Irises
On wet days, it gets saturated, raising humidity and moistening the plant. That can rot the plant.
On the other hand, mulch should be used as a heat reflector. As much as irises love the sun, the rhizomes are sensitive to direct sunlight. The leaves aren’t, but the rhizomes are.
Given these are loosely planted, the rhizomes can be exposed to sunlight. In a heatwave, that will damage their rhizomes. Irises won’t bloom when any part of it is damaged. Instead, its energy will be used up trying to heal.
Grass clippings are often recommended as a suitable mulch to prevent the soil from drying too fast in extreme heat. It can be; however, fresh cuttings are rich in nitrogen.
When using clippings, or any garden debris as a mulch, let them die back a little so they lose their nitrogen content.
Grass clippings should be brown when used as a mulch. Irises are sensitive to nitrogen. They get enough nutrients from water and sunlight.
Fertilizers for irises are low on nitrogen with a higher quantity of phosphorous and potassium.
If you do apply a mulch, remove it as soon as temperatures cool. The risk of mulch is from the reduced air flow and holding water.
Sap-Sucking Pests will Prevent Irises from Blooming
As much are plants are gorgeous to look at and nurture, they do succumb to pest damage and need a little nursing.
The ones that do the most damage on irises are the usual critters with the sharp antennae that pierce into the leaves to drink the sap.
Given irises need a ton of energy, any insect that depletes its nutrients, deprives it of energy. Less energy, less flowers.
Regular leaf inspection is the only way to spot insect damage.
The tricky part is finding them because the most damage is done by the tiniest of mites. The ones you rarely see. Instead of spotting insects, you’re more likely to see their excrements.
All the insects that eat your plant will also poop all over it. It’s called honeydew. It’s an extremely sticky substance that coats the leaves.
Only the insects are parasites, their excrement isn’t. Honeydew on the leaves of irises block the chlorophyll pores, preventing sunlight from reaching the plant.
When that happens, photosynthesis is hindered. Growth slows and will eventually stop. There will be no chance of the iris blooming if the honeydew remains on the foliage. It needs to be washed off.
If it isn’t washed off, the leaves will get coated in sooty mold.
Helping Irises Recover from Sooty Mold
Sooty mold is a fungus but it isn’t parasitic like the bugs are. It only sits on the leaves making it look ugly. Given the substance it grows on, it is sticky so its hard to remove.
It can be scraped off when it’s wet. It’s easier to remove it with neem oil though. That works as a fungicide and a miticide. An insecticide too for most nasty garden critters.
It’s one of the best methods to get rid of bugs on indoor plants. It’s just as effective in the garden, provided it’s applied in the morning or at night.
Coat the leaves in any oil during the high heats of afternoon sun, the leaves will burn. That blackness won’t rub off.
Also, be mindful of the good critters in the garden. Neem oil is a contact insecticide.
It won’t poison passing flying bees, but if you happen to spray it on a plant that has ladybugs preying on aphids, the neem oil will kill the ladybug too. Don’t do that.
Those cute little helpers feed on the nectar of flowers. They don’t have sharp mouths to pierce leaves. They get their nutrients from the aphids, and mites that eat your plant.
Keep the ecosystem in your garden balanced by treating your plants for insects when they are least active. That is early morning before predatory insects come around hunting for breakfast. They’ll help you keep your plants healthy.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.