All about plant fertilization

Fertilizer for Irises – [How and when to fertilize]


Iris is a perennial herbaceous plant that grows from rhizomes or creeping bulbs. It is characterized by its long and erect stems, and its striking and beautiful inflorescences that can be found in various colors such as purple, yellow, white, orange or pink. It is a plant that adapts perfectly to both indoor and outdoor cultivation, and is undoubtedly one of the most popular flowers in gardens around the world. In this post we will analyze everything related to fertilizer for irises which are the best fertilizers, how and when to fertilize, among other important details.


Fertilization in flowering plants such as irises is very important. It can make the difference in having a poor bloom or standing out with an excellent bloom. But as we will see later, we will not only benefit the production of flowers, there are other aspects for which keeping these plants well fertilized is crucial.

Fertilizer for Irises
Interesting fact: this flowering plant has been known and used for thousands of years, in fact it takes its name from the Greek word for rainbow, which is also the name of the Greek goddess of the rainbow, Iris.

1. Preferred Nutrients for Irises


As with all plants in your garden, it’s important to provide them with the proper nutrients. Obviously, irises are no exception. If you have read our blog a bit, surely you have seen how we repeat ourselves about the importance of three fundamental nutrients that are nitrogen (N), phosphorus (P) and potassium (K). In summary, N is key in the development of leaves and stems, P to promote root development, and K helps resist stress and maintain vigour.

But it is not enough to apply those three nutrients and that’s it. The main thing is not to exceed or lack those nutrients. In other words, we must strike a balance so as not to negatively impact the development of our iris plant.

We must strike a balance so as not to negatively impact the development of our iris plant.

Be aware that too much nitrogen can cause excessive foliage growth at the expense of flowering. On the other hand, a phosphorus deficiency can decrease flower production and weaken the roots. And a lack of potassium can make plants more susceptible to disease and heat stress.

2. What are NPK values?


You already know that the main nutrients your plants need are three (N, P, K), but how can we buy the fertilizer we need for each plant? For this there is what is known as NPK values, they define the concentration of these nutrients in a fertilizer.

Surely if you have ever used a commercial fertilizer you will have noticed that there are three numbers separated by a dash on its packaging. Those are, coincidentally, the NPK values.

Let’s take a simple example for you to understand:

If you have a 1 kg packet of fertilizer whose NPK values ​​are 10-5-10. This means that 100 g is nitrogen, 50 g is phosphorus, and 100 g is potassium. The rest is completed with other micronutrients and chemicals added from the fertilizer itself.

In other words, each number represents the percentage by weight of the nutrient with respect to the total weight. I think it’s a pretty simple definition, I hope it’s been clear as we’ll use this concept in the next section.

If you are reading this post, you will probably be interested in learning about fertilizing these other plants.

3. What is the best fertilizer for irises?


3.1 Homemade fertilizer for irises

Our house is always an inexhaustible source of organic matter production. If we know how to take advantage of this detail, we can save a lot of money on fertilizers. In the case of your irises, you can prepare one of these homemade fertilizers:

  • Infusion of eggshells: I have no doubt that you know that eggshells contain calcium, a nutrient that added to those mentioned above is also very important. To prepare this compost you must grind the peels in a food processor or mortar, and then place them in a container with water for a week. After a week you should filter the solution and use it to water your iris plants.
  • Banana peels: Banana peels are rich in potassium. Preparing this homemade compost is easy, you just have to place several banana peels in a container with water and let them rest for a few days. Then it will be enough to remove the husks and use that diluted water to water your iris plants.
  • Compost tea: compost is undoubtedly one of the most complete organic fertilizers, making a tea based on this fertilizer is a good way to take advantage of it. To do this, you must place a quantity of mature compost in a cloth bag and submerge it in water for a few hours or overnight. Then, use the water that the compost has absorbed to water your iris plants.
  • Nettle slurry: to finish I leave you this fertilizer, one of the least known of the four that I listed. To do this, place a handful of fresh nettle leaves in a large bowl and cover with water. Let the mixture sit for a few days, shaking it daily, until it has a strong odor and a greenish-brown color. Filter the solution and use it to water your iris plants by diluting it with water.

Obviously, there are many more homemade fertilizers that can be used on iris plants, but the article would not be enough to list them all. To begin with, these are three very easy to prepare.

3.2 Commercial fertlizer for iris plant

Just as there are many options when looking for homemade fertilizers, it is the same with commercial fertilizers. For this case I have selected four good commercial fertilizers that work very well on irises. I leave them below:

  • Espoma Organic Bulb-Tone: This fertilizer is a rich blend of the best natural and organic ingredients enhanced with an exclusive Bio-tone formula. The NPK numbers of this fertilizer are 3-5-3, it also contains 6% Calcium. Ideal to apply when planting or after flowering in spring
  • Schreiner’s 6-10-10 Controlled Release Iris Food: This is a low nitrogen slow release fertilizer specially formulated for growing Iris. Its formula is 6-10-10 and it is recommended to apply one month before and one month after flowering. It can be obtained in 1 pound bags which yields approximately 25 newly planted Iris.
  • Bayer Advanced Rose & Flower Care: Although this fertilizer is formulated for roses, it is very useful for riris plants. Helps promote the development of strong roots and beautiful flowers. It is also useful as control of some pests and diseases. It has a rainproof systemic protection lasts up to 6 weeks.
  • J R Peters Jacks Classic No.4 10-30-20: This fertilizer releases nutrients gradually for up to 4 months. Its 10-30-20 formula also has micronutrients that provide optimal nutrition for strong roots and green foliage. It is useful for a large number of flowering plants, including irises.

Regardless of the commercial fertilizer that you are going to select for your iris plants, it is always advisable to read the instructions for use carefully. From my experience, having used many fertilizers of this type, I always recommend applying a dose slightly less than what is recommended in the instructions. It is better to go a little short on the dose than not to overdo it, since overdose problems are very difficult to solve.

4. Some questions about iris fertilizers


Before fully entering the final stretch of this post, where we will analyze how and when to fertilize your iris plants, we will stop to answer three frequently asked questions on this subject. Some of them have already been answered if you have read carefully. In any case, I want to make them very clear so that there are no doubts.

4.1 Is bone meal a good fertilizer for irises?

The answer to this question is quite simple, yes bone meal is a beneficial fertilizer for Irises. There are many reasons for this.

As we already mentioned, iris plants require phosphorus for strong root development, healthy flowers, and overall plant vigor. Bone meal is a rich source of phosphorous, so there you have one of the main reasons for it.

Another nutrient that we mentioned as important for irises is calcium. If you know anything about biology, you are sure that bones contain a large amount of calcium. Therefore, bone meal is an excellent fertilizer to provide calcium for your iris plants. In this way you will help to obtain stronger stems and with greater resistance to diseases and pests.

Finally, it’s worth mentioning that irises thrive in slightly acidic to neutral soils with a pH range between 6.0 and 7.5. Bone meal is ph neutral, so when applied to soil it helps bring its ph to neutral levels. Something beneficial for your irises.

4.2 Iris fertilizer 6 10 10 or 5 10 10 – It’s good?

A fertilizer with 6-10-1 or 5-10-10 0 NPK values may be adequate to promote healthy growth and flowering in iris plants. Let’s discuss the reasons behind this recommendation.

As we mentioned in the first parts of the post, nitrogen is good for plant growth. But in flowering plants, an excess of nitrogen can cause an excessive development of the foliage during flowering. Therefore, a fertilizer with a lower percentage of nitrogen (6% or 5%) is a good option.

Then have higher percentages of phosphorus and potassium, both 10% will be good for your iris plants. Phosphorus will help establish strong root systems, which in turn help the plant absorb water. While potassium will increase resistance to diseases and pests, development of strong stems and increased ability to resist drought or temperature fluctuations.

4.3 Is Miracle-Gro good for iris?

Miracle-Gro is a popular brand of water soluble fertilizer that contains a balanced mix of nitrogen, potassium, and phosphorus. It is sold as an all-purpose fertilizer for a broad spectrum of flowering plants. In any case, there are some key points to take into account before applying it to your iris plants.

In general, and as we have been recommending so far in this post, irises benefit from fertilizers with a slightly higher phosphorus content to help develop roots and flowers. So when choosing a balanced Miracle-Gro it may not have the necessary amount of phosphorus.

On the other hand, being balanced you may end up applying too large amounts of nitrogen. And as we have said several times, this can be detrimental to flowering. You should always take care of this point, since what you are looking for are good flowers.

Another point to note is that the Miracle-Gro is quick release. While this may cause you to see almost immediate results, it may not be the best. This will generally lead to rapid foliage growth, at the expense of flower production. In addition, excessive foliage growth can cause weak stems.

With all this I can say that you can apply Miracle-Gro on your iris plants. But this should not be the main fertilizer to apply, you can only use it occasionally and in low doses. Then you will need another fertilizer that provides phosphorus and potassium. To improve the health and flowering of your iris plans.

If you are reading this post, you will probably be interested in learning about fertilizing these other plants.

5. When to fertilize Irises?


So far we have mainly talked about the correct selection of fertilizer. But there is no point in finding the best fertilizer for your iris plant if you apply it at the wrong time afterwards. Knowing when to fertilize these flowering plants is key.

There are several times during the year when you can fertilize your irises. Let’s analyze each of them below:

5.1 Early Spring

One of the ideal times to fertilize irises is in early spring, just as new growth begins to emerge. Fertilizing at this time provides a boost of nutrients when the plants need it most for vigorous growth. It supports the development of strong and healthy foliage, which is essential for photosynthesis and the production of energy reserves in the rhizomes.

5.2 After Blooming

Another opportune time to fertilize irises is after they have finished blooming. Once the flowers have faded and been removed, the plant shifts its energy focus from flower production to replenishing its energy reserves for the next blooming season. Applying fertilizer at this stage helps replenish nutrients in the soil and provides the plant with the resources it needs to strengthen its rhizomes and prepare for the following year’s blooms.

5.3 When not to fertilize?

It’s important to note that irises have a period of dormancy during late fall and winter. During this time, the plant’s growth slows down, and it enters a rest phase. Fertilizing during dormancy is generally not recommended because the plant is not actively growing and cannot efficiently utilize the nutrients. It’s best to wait until spring when the plant resumes active growth.

6. How to fertilize Irises?


We already saw which are the best fertilizers and in which time it is better to do it. It’s time to see step by step how to fertilize your iris plants.

  • Choose the right time: for this you have nothing more than re -read the previous section. In it we have made clear what are the best moments to fertilize.
  • Select the appropriate fertilizer: For this it is good to review sections 3. and 4. of this publication. In these sections we analyze the best fertilizers for iris plants, and we also answer some important doubts.
  • Prepare the area: Eliminate waste or weeds around Liris plants. In this way, it will ensure that the fertilizer reaches the soil directly and avoids any competence for nutrients.
  • Apply fertilizer: Depending on the type of fertilizer you have chosen, the process can change. Anyway, you should always make sure it apply it evenly at the base. And always be careful to maintain a distance of 6 to 8 inches from the rhizome. In this way, it avoids direct contact of fertilizer with the rhizome, something that could cause burns or damage.
  • I water the plants: Once the fertilizer has applied, it is good to water its iris plants well. This helps dissolve the fertilizer and carries the nutrients more deeply to the ground. In this way, roots can better access nutrients.
  • Cover the area (optional): If you want to help maintain moisture, regulate soil temperature and suppress weeds growth, it is a good idea to cover the base of plants with an organic mulch layer. However, be sure to leave a small space between the mulch and rhizomes to avoid excessive moisture accumulation and possible rot.
  • Repeat the applications: depending on the fertilzant that has selected the applications per year that can change. In general, it is necessary to apply 2 or 3 times during the summer spring season.

These are the 7 basic steps to carry out the fertlization of their iris plants. Follow them and will not have byblemas so that the iris become healthy and strong.

6.1 Fertilizing Bearded Irises

Iris is more specifically a genre of plants, within this genre there is for example the bearded iris. These are undoubtedly one of the most popular and cultivated species of iris. They are characterized by having long and sword -shaped leaves, which form a dense and attractive foliage even flourish. The flowers are large and striking, with six distinctive petals that often have a “beard” at the bottom, hence their name.

If what you have is a garden is a bearded iris, and you are looking for how to fertilize it, I have good news for you. Everything you have read in this post applies perfectly to bearded iris. Therefore you can continue step by step everything seen here to know how and when to fertlize this kind of iris.

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