Although they are not demanding, I find that Marigolds (Tagetes) benefit from an organic amendment when planting, together with a light application of an NPK 5-10-5 fertilizer. I only apply more fertilizer before flowering if I see clear signs that they lack nutrients. Avoid overfertilizing by following the packaging strictly.
Signs Your Marigold Is Lacking Nutrients
Identifying whether your plants lack nutrients is challenging because so many factors are at play. Poor soil, bad positioning, insufficient drainage, or insect damage are just some possible causes of poor plant performance.
But, with careful examination and a process of elimination, you can identify nutrient deficiencies in your Marigolds.
Some of the most common signs of nutrient deficiencies are:
- Stringy and sparse foliage
- Twisted or misshaped leaves
- Yellow leaves or brown and yellow spots on leaves
- Leaves turning purple or red
- Lack of flowers
- Pest and disease problems
If your Marigolds are not flowering at their best, the problem is usually a lack of sun. However, it could also be caused by a shortage of phosphorous. If they are well-positioned in the sun, the nutrient problem is the more likely explanation for the lack of flowering (for more, see our in-depth guide to marigold light requirements).
Another sign of a phosphorous deficiency in Marigolds is when the underside of the leave turns purple. So, in your process of elimination, a lack of flowers and purple leaves would be a very strong indicator of a lack of phosphorous.
Follow this same process with the other signs to eliminate other potential issues before turning to fertilizer.
When and How Often Should You Fertilize?
Most Marigold varieties are not fussy about soil but do grow best in rich and well-draining soil. Marigolds that are overfertilized tend to grow foliage at the expense of flowers, so it’s important to feed only when necessary – generally when the soil is of poor quality.
Plant Marigolds in spring after the last frost date when the soil warms. Mix a good amount of organic compost into the soil before planting. If the soil severely lacks nutrients, add a handful of slow-release fertilizer at the same time to improve conditions as the plant matures.
Your Marigolds are unlikely to need more fertilizer than that for the season. But, if you see they are not performing as well as you’d hoped, apply a dose of granular fertilizer right before or just after flowering starts.
Do not feed your Marigolds with fertilizers high in nitrogen, as you will promote the growth of lush foliage over flowers. Choose a fertilizer designed for flowering for the best results.
The Best Fertilizer for Marigold Plants
Start with a good organic compost or well-matured manure. Apart from providing nutrients, this also improves the overall quality of your soil. If you do need to fertilize after that based on your plant’s performance and a soil test, choose a fertilizer with a 5-10-5 NPK ratio or one specifically designed to encourage flowering.
How to Apply Fertilizer
When adding fertilizer to the holes during planting, mix it well and avoid direct contact with the roots. If the fertilizer comes into direct contact with the roots, it may burn them and cause severe damage.
When applying later in the season, spread the fertilizer around the drip line or dilute in water, depending on your chosen product. If there is a chance of run-off, dig the fertilizer granules lightly into the soil to ensure you do not lose valuable nutrients.
Marigolds are not demanding and will survive (and even flourish) without much attention. But, under certain circumstances, they will grow best when given additional fertilizer.
Do not overfertilize, particularly with nitrogen, as it promotes soft leafy growth and hinders the production of flowers. The excessive soft leafy growth, especially in the presence of too much moisture, will encourage powdery mildew. Remember, it’s also prudent to cut back marigolds at the end of the flowering season.
Marigolds can produce sap when cut or handled. This sap can cause skin irritation if it comes into contact with exposed skin, so always wear gloves when handling marigolds.
Fertilizing & Plant Health
With a few exceptions, most plants will grow better when given the right amount of fertilizer at the right time. That is, after all, what it is designed for. The fertilizers add essential nutrients to the soil critical to plant health.
Nutrients are grouped into three different categories: macronutrients, secondary nutrients, and micronutrients. All nutrients are equally important and are essential for plant health, grouped into these categories only because plants require them in different quantities.
Fertilizing your plants is your way of ensuring they have all the nutrients they need to be healthy and thrive (see our guide to marigold growth expectations for more). Knowing what fertilizer is made of helps you understand what type of fertilizer you need, why certain types of fertilizers are better for some plants and not others, and why your plants will need fertilizer applied at different times of the year.
NPK fertilizers provide macronutrients, which should be present in plants at concentrations higher than secondary or micronutrients.
The macronutrients and their main functions are:
- Nitrogen (N) – promotes leaf growth
- Phosphorus (P) – promotes flowering and fruiting
- Potassium (K) – encourages root growth and photosynthesis.
Each macronutrient focuses on a different aspect of plant growth and health. NPK fertilizer is mixed in different ratios, depending on the particular focus of that fertilizer and the impact it is designed to have on your plants.
For example, if you want to ensure that your plants have the best chance at flowering, you will need to buy a fertilizer with a higher phosphorous ratio to encourage flower production.
Secondary nutrients significantly benefit your plants but are required in lesser amounts than macronutrients. The secondary nutrients and some of the more critical roles that they play are:
- Calcium (Ca) – for cell wall formation and improving the absorption of other nutrients.
- Magnesium (Mg) – an essential chlorophyll component that allows plants to manufacture food. Magnesium also acts as a phosphorus carrier in plants.
- Sulfur (S) is important in photosynthesis and is required to synthesize certain amino acids and proteins.
Even though they make up less than 1% of the dry weight of the plant, micronutrients are still critical for plant health. The easiest way to ensure your soil has sufficient micronutrients is by adding organic compost, but specific micronutrient fertilizers are also available if needed.
There are eight essential micronutrients:
- Boron (B)
- Zinc (Zn)
- Manganese (Mn)
- Iron (Fe)
- Copper (Cu)
- Molybdenum (Mo)
- Chlorine (Cl)
- Nickel (Ni).
Types of Fertilizer
There are two primary forms of fertilizer – organic and inorganic. Organic fertilizers are made of natural materials such as peat moss, compost, and seaweed, to name a few. Over time, these fertilizers improve soil health and productivity.
Inorganic fertilizers, as the word suggests, are synthetic. They come in three different forms:
- Liquid fertilizer – usually diluted in water and applied while watering your marigold plants.
- Powdered fertilizer – typically sprinkled onto the soil just before watering but can also be diluted in water.
- Granular fertilizer – often slow-release products worked into the soil as needed. They allow the nutrients to leach into the soil over a longer period whenever water is applied.
Fertilizing Marigold Plants FAQs:
Do Marigold Plants need fertilizer?
In suitable soil, Marigolds don’t need fertilizer to grow well. However, they will generally thrive better in most garden soils with an occasional application as required.
When should I fertilize my Marigold Plants?
Apply fertilizer to the holes when planting in spring if the soil lacks nutrients. Your annual Marigolds are unlikely to require more fertilizer during the season, but they can be applied if the plants are performing poorly.
What is the best fertilizer for Marigold Plants?
Start with a good organic compost mixed into the soil. Then, add granular slow-release fertilizers designed to promote flowering. Use a liquid-based fertilizer for potted Marigolds for easy application and absorption.
Is Miracle Grow Suitable for Marigold Plants?
Miracle Grow Bloom Booster (via Amazon) can be used for Marigolds of all types.
Marigolds have maintained their popularity, and it is not hard to see why. Colorful, symbolic, easy to grow, and beneficial additions to every garden are well worth your time and the little effort it will take to grow these beautiful plants, which also make great cut flowers in bouquet and vase arrangements. Marigolds will benefit from an organic amendment when planting, together with a light application of an NPK 5-10-5 fertilizer.
For more, see our essential guide to everything you need to know about how to grow Marigolds.