Iris plants are cherished for their stunning flowers that come in a diverse range of colors. With proper care, these elegant perennials can continue blooming year after year and add lots of beauty to your garden. One of the keys to keeping iris plants healthy and encouraging prolific blooms is fertilizing them at the right time. This comprehensive guide will explore everything you need to know about when and how to fertilize iris plants.
Overview of Iris Plant Types
There are two main types of iris plants – bearded iris (Iris germanica) and Siberian iris (Iris siberica) The bearded varieties are the most popular garden irises known for their big, showy blooms on tall stems Siberian irises have smaller flowers and thrive in damper conditions. Other iris species like Dutch iris (Iris hollandica) and Japanese iris (Iris ensata) are also commonly grown.
Irises grow from rhizomes which should be planted shallowly in the soil. Proper fertilization encourages the rhizomes to grow and store energy, resulting in abundant blooming. While all iris varieties benefit from feeding, this guide focuses specifically on bearded and Siberian irises which have very similar cultivation needs.
Ideal Time to Fertilize Iris Plants
Fertilizing irises at the right time is crucial to promote lush blooms and healthy plants Irises require fertilizer twice a year – in early spring before flowering and a month after blooms fade. Here are the optimal fertilizing periods
Early Spring
- Fertilize irises just as new growth emerges in spring.
- Ideally fertilize when bulb flowers like tulips start blooming in your region. This is usually March-April.
- Spring feeding encourages excellent root development and stores nutrients for abundant blooming.
After Bloom Period
- Apply fertilizer again after irises finish blooming which is typically June-July.
- Post-bloom feeding helps the plants replenish nutrients and prep for next year’s flowers.
- Fertilize irises immediately after blooms fade, not later.
Late Summer (Optional)
- An additional late summer feeding in August-September can promote root growth before winter dormancy.
- Only fertilize 6 weeks before your first expected frost date.
- This is very beneficial for Siberian irises that grow late into fall.
Choosing the Right Fertilizer for Irises
Picking an appropriate fertilizer is vital for proper iris nutrition. The ideal fertilizer for irises:
- Is a slow-release, granular formula that gradually infuses nutrients.
- Has low nitrogen (the first number on the NPK ratio). High nitrogen causes excessive foliage.
- Contains higher phosphorus (middle number) and potassium (last number) to encourage blooming.
- Has an NPK ratio around 5-10-10 or 5-10-5. A ratio below 10-10-10 is recommended.
Specific fertilizers recommended by iris experts
- Balanced 10-10-10 or 5-10-10 fertilizer.
- Bone meal or superphosphate for phosphorus.
- Alfalfa meal which provides a balance of nutrients.
Avoid quick-release, water-soluble, or high nitrogen fertilizers. Also don’t use compost or manure as this may harbor diseases.
How to Apply Fertilizer to Irises
Proper application technique ensures the irises absorb nutrients through their roots and prevents damage to the plant.
- Read and follow all label instructions for the fertilizer product.
- Use about 1⁄2 cup of fertilizer per mature iris clump. For potted irises, use 1⁄4 cup.
- Spread the fertilizer evenly around the plant about 6-12 inches from the base.
- Gently mix the fertilizer into the top 1-2 inches of soil using a trowel or cultivator.
- Water the irises thoroughly after feeding to dissolve nutrients into the soil.
- Never allow fertilizer to touch the leaves, stems or rhizomes.
Signs Your Irises Need Fertilizer
Monitor iris plants regularly for signals they need more nutrients. Common deficiency signs:
- Sparse flowers or reduced blooming.
- Yellowing leaves and lackluster foliage.
- Poor rhizome growth and easily uprooted plants.
- Increased pest and disease damage.
If you notice these issues, fertilize as soon as possible per the spring regimen. Also adjust soil pH if needed since irises prefer slightly acidic soil.
Benefits of Proper Fertilization
Fertilizing irises at the ideal times and with the right products provides many benefits:
- Promotes extensive root systems and vigorous rhizome growth.
- Encourages taller, stronger foliage that resists flopping.
- Enables plants to store more energy for abundant blooming.
- Supports bigger blooms with richer, more vibrant colors.
- Boosts overall plant health, wards off pests, and prevents diseases.
- Prepares irises for winter dormancy and next year’s growth cycle.
Common Iris Fertilizing Mistakes
Some common mistakes to avoid when feeding irises include:
- Using quick-release or water-soluble fertilizers that cause rapid growth.
- Applying high nitrogen fertilizer that results in floppy plants.
- Fertilizing at the wrong time such as during summer dormancy.
- Allowing fertilizer to touch the rhizomes leading to rot and death.
- Applying too much fertilizer which can burn roots and leaves.
- Forgetting to fertilize newly planted irises which need nutrients to establish.
- Not watering after fertilizing so plants can’t absorb the nutrients properly.
Fertilizing iris plants at the right time with an appropriate nutrient ratio plays a major role in their health and productivity. Follow the tips in this guide to determine the ideal fertilizing periods for your climate and select a suitable fertilizer product. With just two or three yearly feedings, you can enjoy thriving, floriferous iris plants that provide stunning color in your garden year after year.
Pre-Bloom Care for your Bearded Iris with Ben Schreiner.
FAQ
What is the best fertilizer for iris?
Because phosphate is important, we recommend bone meal or super-phosphate and a light balanced fertilizer such as 10-10-10 or 6-10-10 depending on the amount …
What month do you cut back irises?
- Timing is Key: Wait for the first few frosts to kill off the iris foliage, then cut back the plants.
- Why Cut Back? Cutting back irises after flowering and after the foliage has died helps prevent diseases and pests, especially iris borers, from overwintering in the leaves.
- How to Cut Back: Cut the foliage back to 6 to 8 inches above the ground.
- After Flowering: Once the blooms are finished, remove the spent flower stalks down to the rhizome.
- Leave Green Foliage: As long as the foliage is green and attractive, leave it in the garden, as it continues to produce energy for the plant.
- Consider Dividing: If your irises haven’t bloomed well, they might need dividing, or they could be in too much shade.
- Fertilize: Fertilize your irises with an organic fertilizer in the spring.
How do I encourage iris to bloom?
An amendment of superphosphate, colloidal phosphate, or bone meal applied in early spring can help plants develop blooms.Apr 21, 2021
Is Miracle-Gro good for irises?
Fertilizing Iris
Provide a light application in early spring and again a month after bloom. Place fertilizer around rhizomes, not directly on them. Alfalfa pellets (without salt) are extremely beneficial when incorporated in the soil around the newly planted irises. Do NOT use Feed & Weed preparations or Miracle Grow.
When should I fertilize my Iris?
When a particular type of iris blooms impacts the ideal time to fertilize it. The plants benefit from being fed twice a year, in early spring and around a month after they have finished flowering.
Do Irises need fertilizer?
There are other key times in the lifetime of an iris when it will benefit from fertilizer. It is beneficial to add fertilizer when you plant iris bulbs, along with when you split irises. Irises want fertilizing before and after blooming
How do you fertilize irises?
Irises appreciate a granular, slow-release fertilizer applied before and after the normal blooming period. Spread the fertilizer in a ring around the plant, near the root zone, and avoid getting the feed on the rhizome or foliage. Gently scratch the fertilizer into the top layer of the soil and water the root zone well.
When should I fertilize my bearded iris?
The plants benefit from being fed twice a year, in early spring and around a month after they have finished flowering. ‘The best time to fertilize bearded iris is before their blooming season, usually right about when tulips start blooming in your area,’ advises Mike Sutton from Sutton’s Iris Garden.
What is the best fertilizer for Iris?
Phosphorus is essential for root and stem growth and is especially important for blooming plants. A balanced fertilizer that is high in phosphorus and contains other essential nutrients such as nitrogen and potassium is the ideal choice for iris. It is important to choose a fertilizer that is specifically designed for iris.
When should irises be planted?
It is important that the roots of newly planted irises be well established before the end of the growing season. Plant your iris at least four to six weeks before your first hard freeze or killing frost. Irises require at least a half-day (6-8 hours) of direct sunlight.