When it comes to propagating rosemary, many gardeners are tempted to give their cuttings a head start with a bit of fertilizer. After all, young plants need nutrients to grow, right? Surprisingly, this well-meaning approach is actually very likely to backfire and damage or even kill the young plants.
You should not fertilize rosemary cuttings because they thrive in low-nutrient environments. Fertilizer can lead to root damage and negatively impact the plant’s overall health. Even older rosemary plants rarely need fertilizer, although, it can be beneficial during their active growing season in spring and early summer.
Over-fertilizing rosemary is an easy mistake to make, especially with younger plants or cuttings as they can’t take much fertilizer before they begin to take damage. Since most of the damage happens to the roots, it can be difficult to identify the problem before it is too late, but if you know what to look for, you will be better prepared. I cover what you need to know in this article.
But first, I want to go into a bit more detail about what happens to your rosemary cuttings or plants if you fertilize them when they are too young.
Why You Should Not Fertilize Your Rosemary Cuttings
It might be tempting to give your rosemary cuttings a boost with some fertilizer, but it should be avoided as it will almost certainly do more damage than good. Let me explain why.
Fertilizing rosemary cuttings or young rosemary plants can inhibit their critical early-stage root development. Fertilizing them will likely lead to root burn or stunted root growth, thereby damaging the plant as a whole.
Cuttings need to focus on establishing a strong root system to support future growth before fertilizer is introduced.
Additionally, using a nutrient-rich fertilizer, especially nitrogen-heavy ones, can promote excessive foliage growth at the expense of root development. This imbalance can result in weak roots that are insufficient to support all the foliage, eventually causing the plant to die.
Therefore, refrain from giving your rosemary cuttings or very young plants any fertilizer. It will allow them to focus on root development, which creates a strong foundation for healthy future growth.
Only Give Your Rosemary Fertilizer in This Situation
The only situation when you should give your rosemary fertilizer is when the plant is well-established (meaning not young plants or cuttings) and shows clear signs of nutrient deficiency.
This typically means:
- Yellowing or pale leaves
- Slow growth despite adequate space, sunlight, and water
- If the plant is growing in very poor-quality soil
In these cases, it can be beneficial to use a balanced fertilizer with a lower nitrogen content to avoid excessive foliage growth at the expense of root development.
Only consider giving your rosemary fertilizer in the spring or early summer when it is in the growing stage of its annual cycle.
Rosemary slows its growth in the winter. Reduced growth means reduced nutrient uptake, so fertilizing in the winter can lead to nutrient buildup in the soil, which can be harmful to the roots and thereby the plant as a whole.
Never fertilize rosemary cuttings or very young plants.
What Type of Fertilizer To Use for Rosemary (And How Much)
As a general rule, rosemary rarely (if ever) needs fertilizer and fertilizing it will often damage it rather than boost its growth. I have already covered this in detail in this article, so instead of repeating myself, here is how to pick the right type of fertilizer for your rosemary for those situations where it should actually be fertilized.
It is best to use a balanced, slow-release fertilizer with a lower nitrogen content and higher phosphorus and potassium for rosemary.
This type of fertilizer is suitable because rosemary prefers soil that is not too rich in nitrogen as excessive nitrogen promotes foliage growth, sometimes at the expense of root development. Phosphorus and potassium, on the other hand, are beneficial for root development.
5 Signs You Are Over-Fertilizing Your Rosemary
Over-fertilizing rosemary will damage the plant and its roots. It is not always easy to notice the damage early, but if you know the signs to look for, you have a much better chance of saving your plant.
Here are the signs that your rosemary is over-fertilized.
Leaf discoloration
Rosemary leaves will often start to turn yellow or brown at the tips when it is over-fertilized or growing in too nutrient-rich soil.
Stunted growth
Over-fertilization damages the roots, which itself is not visible since it happens underground. A consequence of this is that you will see stunted growth since the plant isn’t able to obtain the nutrients and water it needs because of the root damage.
Leaves curling up
One of the most common signs I have seen of rosemary being over-fertilized is that some of the leaves will curl up, which you can see in the photo above. It is usually accompanied by discoloration of the leaf.
Leaves falling off
Over-fertilized rosemary can drop leaves prematurely. It can happen because the plant is under stress from nutrient imbalance.
Wilting
Over-fertilized rosemary will often wilt. This happens because the roots are under stress and potentially being damaged by the excessive amount of nutrients in the soil. This root damage impacts the plant’s ability to obtain the water and nutrients it needs, which causes it to wilt.
In my experience, wilting and leaves turning brown and curling up are the most common and clear signs of rosemary being over-fertilized. The photo above is an old rosemary plant I had a while ago where you can see both wilting and leaf discoloration and that the leaves are curling up.
What To Do if Your Rosemary Is Over-Fertilized (4 Tips)
Once you notice the signs of over-fertilizing on your rosemary, it might be too late to save it but there are a handful of steps you should take to have the highest chance of saving it.
- Prune away damaged foliage
- Repot the plant into a larger pot and add fresh soil (if it is potted)
- Water generously for a few days to wash out excess fertilizer
- Avoid using more fertilizer until the issue has been resolved
In my experience, repotting rosemary can be a good way to solve certain problems, but if you do that, make sure you don’t scrape away all the old soil to replace it with new soil as that can cause additional stress on the roots. Instead, transplant the plant into a larger pot in which you add extra soil to dilute the concentration of fertilizer around the roots. If this is relevant to you, check out my guide on how to repot rosemary.
Watering generously is also a great way to wash out some of the excess fertilizer. Just make sure you don’t do it for more than a few days to a week in a row since it can lead to overwatering and root rot.