Flowers, Ornamental Gardens

Mexican Sunflower: Must-Grow Tithonia Plants


Mexican sunflower

There are actually two plants that qualify as Mexican sunflower, both of which are Tithonia species. Tithonia rotundifolia is also called the “red sunflower,” but Tithonia diversifolia has a slew of names ranging from “Japanese sunflower” to “tree marigold” or “Mexican tournesol.” 

Both share the common name “Mexican sunflower,” but the former is orange-to-red in color, and the latter is yellow. Each Mexican sunflower is so closely related that their care is identical. Both are native to Mexico. They’re both great plants for drawing in butterflies, and hummingbirds love them! 

Any master gardener will tell you Mexican sunflowers make a great addition to any butterfly garden as they are known for attracting many beneficial insects, including monarch butterflies. Grow Mexican sunflowers alongside milkweed (the monarch butterfly’s host plant), castor bean plant, flowers that look like sunflowers, and other butterfly-friendly plants in order to provide them with an additional food source. 

Tithonia diversifolia is a little more widespread than Tithonia rotundifolia (common red sunflower), but both are common garden plants. To prevent confusion from here on out, we will discuss T. diversifolia. This easy plant is in the Aster family and has flowers that resemble marigolds (which are also in the Aster family!). 

In both cases, Mexican sunflower care is the same. Now, let’s talk about how to grow Mexican sunflowers!

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Quick Care Guide

Tithonia diversifolia
Tithonia diversifolia. Source: Starr
Common NameTree marigold, Mexican tournesol, Mexican sunflower, Japanese sunflower, Nitobe chrysanthemum
Scientific NameTithonia diversifolia
FamilyAsteraceae
Height & SpreadUp to 8 feet tall by 3 feet wide
LightFull sun
SoilWell-drained
WaterDrought tolerant once established
Pests & DiseasesSnails and slugs, powdery mildew

All About Mexican Sunflowers

Monarch butterfly on an orange Mexican sunflower
Butterflies love to land on Mexican sunflowers. Source: kendoman26

Mexican sunflower (Tithonia diversifolia) are also known as tree marigold, Mexican tournesol, Japanese sunflower, Nitobe chrysanthemum, or simply Tithonia. As their name would suggest these flowers originate from Mexico and Central America. They are grown as annuals in most areas but can be grown as perennials in USDA zones 9-11. In warmer climates, they can be cut back to the woody growth in late fall/early winter and they will grow back in the spring. 

Although Mexican sunflower is the most common name for this plant, tree marigold seems like the most appropriate name. They can grow to be 8 feet tall and resemble a small tree! And the flower more closely resembles that of marigolds rather than true sunflowers. The Tithonia flower can come in a variety of colors, but the most popular are shades of red, orange, and yellow. T. diversifolia is most often yellow. 

Growing Mexican sunflower is so easy that you might even do it by accident! They have the ability to set roots from any point on the stem, much like a tomato. This means that if one of these sunflowers falls to the ground it then has the ability to root itself and grow a new flower. It is this growth habit that has led to it being considered invasive in some areas. 

All that being said, because of its aggressive growth, it can be used as a source of biomass and used to add organic matter to other areas of your garden. When using them this way it is important to run the stalks through a chipper or chop them finely to avoid them spreading to an area where you don’t want them. This way you can grow your own fertilizer! 

Mexican sunflower plants have been referred to as the comfrey plant of the south, and pound for pound provide nutrients equivalent to chicken manure. For this reason, it has also been referred to as vegan manure. Because Mexican sunflower care is so minimal, you’ll have great success using this way.  

If you’re concerned about dedicating a large amount of vertical space to the Mexican sunflower, then never fear! There are also dwarf varieties that won’t grow as tall such as Fiesta del sol. These smaller plants don’t take up as much space and still offer beautiful cut flowers from the garden. 

Caring For Mexican Sunflowers

Tithonia diversifolia flower
A good view of the Tithonia diversifolia flower. Source: Anita363

Mexican sunflower care is minimal which makes them a perfect plant type for the beginner gardener. Read on to learn how to keep these beautiful yellow flowers blooming all summer. Give them enough space in your garden and their blooms will attract many pollinators including butterflies – like the monarch butterfly – and hummingbirds. 

Sun and Temperature

Mexican sunflowers love full sunlight. They require 6-8 hours of sunlight per day and can be very drought tolerant once established. If you grow Mexican sunflower plants in partial shade, they will not produce blooms as profusely and will not grow as tall. They may even grow spindly, lanky, and flop over from a lack of sunlight. 

USDA growing zones 9-11 most closely resemble this plant’s native habitat. These plants are extremely sensitive to frost and cool weather and should not be grown outdoors until nighttime temperatures heat to 60 degrees Fahrenheit and above. 

For this reason, in milder climates with frost looming, you may want to start your Mexican sunflower seeds indoors in containers (like our Epic 4-cells) about 6-8 weeks before your last frost date to ensure that this plant has enough time to grow and flower in summer. This head start after the last frost will ensure that your Mexican sunflowers have enough time to grow lovely blooms. 

In warmer climates without as much frost, you may choose to sow seeds directly into your garden. Always consult the packet of your Tithonia seeds before you sow directly for the length of time from seed to summer bloom. 

Water and Humidity

Planting a Mexican sunflower seedling will require more water than an established Mexican sunflower plant. While they are young be sure to water your sunflower plant deeply and often (at least two times per week). Water in the morning at the base of the plant and avoid wetting the foliage and blooms as they can suffer from mildew. 

For this same reason, this plant type doesn’t enjoy high humidity, and plants need to be properly spaced in the garden to avoid overcrowding and increase airflow. Once the bloom season has come to an end, you can cease watering your plants. It’s also important to note that this plant does not like wet soil, so when in doubt, it’s better to underwater rather than overwater the sunflower garden. 

Soil

Mexican sunflowers can tolerate poor soil conditions and have been known to thrive in sandy and rocky soil. As mentioned above the most important consideration for your garden soil when you are growing Mexican sunflowers is that it is well-draining in order to avoid consistently moist soil. Your soil should be able to dry out between waterings. Mexican sunflower plants can also tolerate a variety of soil pH levels and can even tolerate slightly acidic soils. 

Fertilizing Mexican Sunflowers

As mentioned above, Mexican sunflower care is minimal. For this reason, this plant doesn’t require any fertilizer at all. The addition of some organic matter to the garden planting site at the beginning of the growing season should be sufficient. Once established, they don’t require much in the way of watering, nor do they require fertilizing. Deadheading the spent blooms will encourage more flowers than any fertilizer will. Not to mention, Mexican sunflower plants can be chopped and dropped into the garden and used as a fertilizer for other plants in your garden. 

Pruning & Training Mexican Sunflowers

Tall Mexican sunflower plant
Mexican sunflowers can grow to be quite tall. Source: Starr

As previously mentioned, deadheading spent blooms is necessary for flower production, more so than the addition of fertilizers. Once the bloom of your Mexican sunflower plants has faded, simply cut them back at the nearest growth point below to encourage bushier growth, and more blooms will soon appear. 

Without deadheading, you will get fewer blooms overall, and the Mexican sunflowers may grow too tall to support themselves and require staking or training up a trellis. You may also find your sunflower has done the planting of seeds without you, as seeds germinate in spring and flowers bloom in summer. 

One of the most important parts of learning how to grow Mexican sunflowers is deadheading. Deadheading prevents the spreading of seeds that gives Tithonia its invasive reputation. By removing the plant’s seeds from the garden, you’ll save space for other flowers in summer. 

Mexican Sunflower Propagation

Now that you know how to care for Mexican sunflowers, you may be wanting more of them and wondering how to propagate Mexican sunflower. The best and easiest method of propagation for these plants is to start them from seed. In USDA zones 9-11, you may choose to plant seeds directly outdoors or start seeds indoors and transplant Mexican sunflower seedlings in order to get earlier blooms. 

In milder climates with a shorter growing season, it’s recommended to start the seeds indoors for planting outdoors at a later time. Consult the back of the seed packet for recommendations specific to your area. 

Since these sunflowers put out aerial roots, they can also be propagated from stem cuttings. Like tomato plants, Mexican sunflowers can put out roots all along their stem. Remove a section of the stem just below a leaf node. Be sure that the cutting has at least 2-3 leaves. Place the cutting directly into a pot with soil and keep well watered in a sunny window indoors. Roots will establish within 2 weeks, and they can then be transplanted outdoors.  

Troubleshooting Mexican Sunflowers

Tithonia diversifolia spent flowers
Spent Tithonia diversifolia flowers on the plant. Source: osahiro_nishihata

The Mexican sunflower plant is a relatively carefree and no to low maintenance plant. However, there are some signs to look out for when growing Mexican sunflowers that could indicate an underlying issue. 

Mexican Sunflower Growing Problems

As mentioned above, growing Mexican sunflowers requires full sun. Most of the growing problems that occur with this plant are a result of a lack of sunlight. If you notice that your plants aren’t blooming in the butterfly garden, that growth seems slow, or that plants are spindly and lackluster, then this could be a result of a lack of sun. 

There is no way to remedy a lack of light other than to use caution when choosing a planting site for your sunflowers prior to the time you plant seeds. Be sure to choose a spot to grow Mexican sunflower in your garden that receives 6-8 hours of sunlight per day and is not shaded out by any other plants or structures. 

Since these flowers are known to grow quite tall, they can also be knocked over if grown in a windy or exposed area. It’s not impossible to grow Mexican sunflowers or start seeds in these types of areas. However, you may need to provide support like a trellis or stakes in order to keep them upright. 

Pests

Since sunflowers are native to Mexico, these Tithonia plants are well suited to drought and dry conditions. Therefore most of their pest issues are a result of wet weather conditions. Slugs and snails can sometimes bother Mexican sunflowers, especially after extended rainy conditions. If you notice irregular holes in the foliage after prolonged wet weather, then this may be a sign of snails or slugs. 

A wet piece of cardboard can be placed near where you grow Mexican sunflower to act as a trap. These pests will seek out the cardboard as shelter during the day and can then be easily collected. Iron phosphate has been known to control snails and slugs in more extreme infestations, or organic slug & snail baits can be applied. 

Diseases

When you learn how to grow Mexican sunflower, you’ll find overwatering can cause the perfect conditions for fungus to take hold, especially in hot and humid climates. If too much moisture is splashed onto the foliage during watering, then this can contribute to issues with powdery mildew. This mildew appears as a white flour-like powder on the leaves. 

To prevent these issues, always bottom water your plants. Neem oil may also be sprayed as a preventative measure to reduce the colonization of spores on foliage. In advanced cases of this mildew, removing and destroying infected plant material may be best to prevent it from spreading to nearby healthy plants. After removing infected material (stalks, seeds, and flowers), spray neem oil or a liquid copper fungicide onto the remainder of the plant and nearby plants to reduce the risk of further spread. 

Frequently Asked Questions

Mexican sunflower
Mexican sunflower is a gorgeous pollinator plant and garden asset. Source: Starr

Q: Do Mexican sunflowers come back every year?

A: Mexican sunflower (Tithonia plants in general as well) will need to be planted again each spring in mild climates. In USDA zones 9-11, you can grow Mexican sunflowers as perennials. 

Q: Is the Mexican sunflower an annual or perennial?

A: Mexican sunflowers are annuals in most areas. 

Q: Is Mexican sunflower invasive?

A: T. diversifolia is considered invasive in Florida, but T. rotundifolia isn’t, and in most of the western US both are used interchangeably. That means you can grow Mexican sunflowers anywhere safely.

Q: Will Mexican sunflower reseed itself?

A: Yes, although Tithonia is an annual, it will readily reseed and come back year after year with little intervention. In warmer climates such as USDA zones 9-11, you can grow Mexican sunflowers as perennial plants.  

Q: Do Mexican sunflowers need full sun?

A: Yes, grow Mexican sunflowers in full sun or 6-8 hours of sunlight per day. 

Q: How long does it take for Mexican sunflowers to bloom?

A: Consult the Tithonia seed packet for planting information about the exact days to bloom. However, most Mexican sunflowers will bloom in midsummer and into the winter in warmer climates. 

Q: How do you cut and drop a Mexican sunflower?

A: Tithonia plants produce aerial roots, kinda like tomatoes do — you can cut & drop the leaves with no problem, but it’s better to chop the stems into fine particulate, so you don’t accidentally propagate the thick stems and make new plants!

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