Irises are one of the most iconic flowers around. They’re also one of my personal favorites. While most of us only see irises in bouquets, I wanted to learn how to grow iris in pots.
It turns out, these flowering beauties do very well in containers.
You can grow iris in pots that are 10 to 12 inches deep and wide. You want to keep the soil moist but avoid overwatering them. You should provide organic fertilizer to the iris every month during the growing season.
1. Choose the best time to grow iris
If you’re familiar with iris flowers, you already know that they come in a wide range of colors. Believe it or not, there are reportedly over 300 different iris varieties out there.
For the most part, gardeners separate irises into two distinct categories: bearded and crested. Bearded irises are the most common and typically do better in pots. That’s because they have thick fleshy roots that grow closer to the soil’s surface. They don’t need a ton of depth, making them a good candidate for container growing.
You can identify bearded irises from the petals. They feature rows of fuzzy hair on the fall petals.
Crested irises can grow in pots as well. Though, you have to be a bit more selective to ensure that you’re getting a strong variety. These irises are low-growing and can spread rapidly. Thus, they can get out of hand pretty quickly.
Regardless of the type of iris plant you grow, timing is key. The best time to plant any iris is going to be sometime around the late spring and early fall.
The exact timing will depend on your region. Keep an eye on nightly temperatures. When the nighttime lows are between 40 and 50 degrees Fahrenheit, you’re good to go. Planting at this time ensures that the plant has enough time to establish itself before the temperature drops more for winter.
Now, there may be some wiggle room based on the variety you choose. For example, crested iris varieties are more forgiving when it comes to planting time. But, bearded irises are best when planted closer to fall because they go dormant in the middle of summer.
2. Find out how long iris takes to grow
Determining the growth cycle of an iris plant is tricky.
You see, the plant itself will grow without too many issues. It can start generating leaves and long stems the first spring after planting. But will it start producing blooms? Well, that depends on the growing environment.
Some irises can take years to start producing flowers. The root rhizomes will develop under the soil and may even produce seed pods that set. However, conditions might not be right to create flowers that you can enjoy.
About 60 to 75 percent of new iris plants will produce flowers within the first year. The remaining plants may need a year or two to establish.
These plants can take some time to see results. Even germinating seeds is a lengthy process that can last three months or more.
When Do Irises Bloom?
When they are ready, most cultivars will bloom in the early spring and summer. But even then, there are a lot of factors to contend with.
Some plants will only bloom for as little as two weeks. Others may have a late start, which cuts the blooming period short. It all comes down to weather and growing conditions. Irises are notoriously finicky.
3. Choose the right pot to grow iris
Irises can do very well in pots. But, you need to choose the right container to see the best results.
Your pot should be able to hold at least 2 gallons of soil. For dwarf iris varieties, go for a pot that’s 6 to 8 inches in diameter. But if you want a tall bearded iris, you’ll need to use a pot that’s at least 12 inches in diameter.
For material, you have a lot of options. There aren’t any strict requirements about the type of pot your iris should grow in. In fact, many gardeners opt for unconventional containers like barrels or large tubs. As long as the container has enough room for the plant, it’s suitable.
If you want to provide the most protection for the plant as possible, use a thicker pot material like terracotta or ceramic. Irises need to have some winter exposure to promote flower production. But, they still react negatively to cold weather.
A thicker pot will provide more insulation to keep the soil moist during the cooler months.
I like ceramic pots because they help absorb moisture from the soil and protect the plant roots from overwatering problems.
4. Prepare the pot to plant iris
Before you start planting, there’s some extra work to do on your pot. The goal is to create a conducive growing environment that mimics an open garden bed.
One of the biggest issues gardeners face with container growing is a lack of proper drainage. Iris plants need well-draining soil. If water can pool inside the container, you’ll run into issues that will stunt the growth of your plant.
If a potted plant is overwatered it will cause root rot that damages the roots. They won’t be able to supply the nutrients and moisture to the plant causing lack of growth or death.
I’ve written a post that will help you prevent overwatering the potted plant and recover the plant if you are facing the issue.
Take a look at the bottom of the pot. Make sure it has several drainage holes. If it doesn’t, make some. You can use a drill to pop a few holes in the bottom and give water more opportunities to flow out.
Once that’s done, you can focus on preparing your soil.
Iris plants need fertile soil that’s on the acidic side. These flowers aren’t like other acid-loving plants that need major soil amendments. The ideal pH balance is 6.8, which is just a hair below neutral.
Use a soil testing kit to take some baseline measurements. If your soil is neutral or alkali, add a bit of peat moss into the mix. Don’t go overboard here. Remember, the soil needs to be only slightly acidic.
It’s best to prepare the soil several months in advance. Adjusting the pH balance takes time. Once you add the peat moss, retest the acidity every month and make adjustments accordingly.
As you’re waiting for the peat moss to work its magic, you can also add compost to your soil. Organic compost will infuse the soil with nutrients that your plant can use to grow.
I recommend adding compost to the potting soil because it improves the texture, provides nutrients, and encourages beneficial organisms. You can find 7 expert tips on adding compost to your iris plant.
5. Plant the iris plant in the pot
There are a couple of different ways to grow iris plants. You can start them from seed or rhizomes.
Starting from Seed
Growing from seed is no easy task. It takes a lot longer and there are a lot of things that can go wrong. For this reason, most gardeners don’t opt for this route unless they have a lot of experience.
But if you’re comfortable with the work ahead, growing from seed can provide you with greater control over the growing environment.
When you’re ready to plant, soak the seeks in clean water for about three to five days. Don’t forget to change the water frequently to prevent any fungal problems.
Dry the seed out and prepare your pots. Bury the seeds about half an inch below the surface of the soil. Don’t stack seeds or spread them randomly. Instead, strategically place them a few inches apart. You’ll thin seedlings later, so you can add several seeds to a pot.
Now, put your planted seeds indoors under a grow light. When the temperature drops, overwinter the seeds outdoors. This will break the seed’s dormancy and promote growth. You can leave them outside as long as the temperatures don’t get too close to freezing.
It can take several months for sprouts to appear. But once you see them pop up, move them to a sunny spot for further growth.
Starting from Rhizomes
Rhizomes are like bare-root plants. Many gardeners refer to them as bulbs. While similar, rhizomes are actually swollen stems that develop a root system. They are propagations from a mature plant, so there’s a greater chance of success.
Dig a shallow hole in your pot that’s roughly 4 inches deep. Then, create a little ridge in the center of the hole. Set the rhizome on top of the ridge and let any roots spread down the side. The rhizome should look horizontal.
Fill the rest of the hole and cover most of the rhizome. But, leave the top exposed. The rhizome needs some exposure to cooler weather to grow. So, don’t cover it with soil or bury it too deep.
Plant propagation is one of the best and cheapest methods to grow plants. Check out my post on how you can use this method for growing iris plants.
6. Place the iris pot in the right location
To reach its full potential, iris plants need full sun. It’s best to position the plant so that it can get full exposure throughout the day.
These plants can tolerate partial shade. If you have no other options, only a half-day of sun exposure will suffice. However, exposure to partial shade will result in fewer blooms.
Irises are sun-loving plants and are often the first flowers of the season to bloom. But they need the right conditions to do that. Put your plant on the south-facing side of your house. Make sure that the plant is clear from nearby plants, trees, or structures that could cast a shadow.
Only in cases of extreme heat should you purposely block the sun. In hotter climates, the excess heat could damage the plant, so partial shade can be beneficial. But even then, this should only be a temporary measure for hotter days.
7. Provide sufficient water to the iris plant
Like any other plant, irises need water to grow. That said, you can’t water these plants frequently. They are very sensitive to overwatering. The exposed rhizomes can quickly rot out in standing water.
Not only will this stunt the growth of the plant, but it could kill it outright.
Irises need consistent and deep waterings. But chances are, those waterings will be less frequent than you’re used to with other perennials.
It’s best to wait until the top 3 inches of soil dry out before you water the plant. Generally, this is every other week. Timing can depend on your environment. In warmer areas, waterings could be a bit more frequent. You don’t want drought to kill your plant, so check the soil frequently with your finger to get a better idea of the plant’s needs.
The easiest way to water your iris is to simply pour water at the base. Using a gently watering-can, focus the stream on the soil surrounding the root. Pour slowly to let the water soak into the soil fully. It should start running out the drainage holes in the bottom.
That’s easy enough. Yet, there’s another method that many gardeners use to keep the foliage protected. It involves a large tub.
Fill a large tub up with about 3 inches of water and set your pot inside. The goal here is to water from the bottom up. Let the soil absorb water through the drainage holes. When the top of the soil in the pot is moist, you’re good to go.
8. Prune unwanted parts of the iris plant
Pruning your iris can help extend its growth cycle. While there are no guarantees, proper pruning may result in additional blooms later on.
The best time to prune is after the plant goes through a blooming cycle. Keep an eye on the stalks. You may see numerous blooms appear on a single stalk before the plant finishes.
Once all of those flowers open and die off, cut the stalk all the way to the ground.
This serves a couple of different purposes. First, it prevents the plant from forming seeds. Seed formation follows the blooming cycle. But when you cut the stalks, it encourages the plant to focus its energy on creating more flowers. So, you may see another blooming period late in the summer.
Secondly, pruning helps to conserve energy. Seed formation takes up a lot of energy. We want that energy to go to the roots and foliage instead. Cutting the stalks and preventing seeds can do just that.
Depending on where you live, you might want to do a second prune in the fall. In areas with mild climates, iris plants can stay green throughout the winter. Plants in areas that experience cold winters, however, will start to die back.
When this happens, the leaves turn yellow and start to shrivel up. Cut those dying leaves back to about 6 inches. This prune ensures that the plant uses its energy for root growth rather during the winter season.
9. Add fertilizer to the iris plant
Strategically timed fertilizer applications can do a lot to push your plant further. The goal here isn’t to support the plant’s primary growth. Hopefully, adequate soil preparation before planting will take care of that.
Instead, your fertilizer application should help with bloom production.
Use a standard all-purpose fertilizer product for your irises. Avoid anything high in nitrogen. Nitrogen will only develop more foliage.
Dry granules are best. You have to be careful to not burn the plant or its roots. Thanks to the exposed rhizome, water-soluble formulas will not do.
Gently scratch the fertilizer into the soil around the root. Use your finger to create a small ridge. Then, sprinkle the granules in.
Use this application method to feed your plant in early spring. Once your plant has gone through the blooming cycle you can apply another dosage. You should do this after pruning. The second application can help promote an additional blooming period in the summer.
You can use one of the 27 best natural fertilizers for your plants. Just make sure to use something that is lower in nitrogen and higher in phosphorus and potassium for good flower growth.