Mexican Sunflower (Tithonia Diversifolia)

This attractive flowering shrub is also great for restoring depleted soil; plant it in the fall for great garden soil in spring

One of our Mexican sunflower (Tithonia diversifolia) plants in early June

Mexican Sunflower (Tithonia diversifolia) is one of those plants that’s a perfect combination of easy to care for, attractive, and beneficial for the garden. It’s one of my favorites in multiple areas of the Acre.

Mexican sunflower basics

Also known as Tree Marigold, Mexican Tournesol, Japanese Sunflower, or Nitobe Chrysanthemum, the Mexican sunflower is originally native to Mexico and Central America. These days, however, it’s adapted to the warmer temperate and sub-tropical environments on every continent.

The plant is a woody shrub that will grow from 6 to 10 ft (2-2.75 m) and spreads equally wide.

Mexican sunflower bush in late spring about 8ft tall and 10ft wide

In warm climates (USDA hardiness zones 7 and up), this type of tithonia is a perennial that grows quickly in late winter and early spring, blooming with bright 6-inch yellow flowers in all but the hottest part of summer. In cooler zones, it’s an annual that will bloom from late spring through fall.

Care Requirements

The Mexican sunflower is a very low-care plant. It thrives in full sun or partial shade and will grow in nearly any type of soil. The plant is also drought tolerant and well-adapted for environments where it gets a lot of rain in one season and remains essentially dry for the rest of the year, making it a perfect plant for the arid American southern plains and southwest.

The Mexican sunflower plant is drought resistant

If the plant gets more water, it can get weedy and spread quickly. It is considered invasive in tropical regions like south Florida and Hawaii.

Plant Uses

Garden Screen

Aside from being a showy, flowering plant, it grows tall and relatively dense, making it a good screen for hiding fences, walls, and other objects. I use it as a hedge to obscure a low chain link fence near the front courtyard, as well as screen out a shed and the side of my neighbor’s house in a couple of other areas.

This tithonia screens a low chain link fence near the courtyard

As the plants get later in the season, the lower leaves will die back, creating a sort of tree-like forest of long, woody (but soft) stems, topped with green leaves and flowers. Walking among them is a lot like walking through a forest in a Dr Seuss book.

The reason tithonias are also known as “Tree Marigolds”

Cut Flowers

The Mexican sunflower blooms continuously throughout the season, and cutting the flowers encourages more flowers to grow. Better yet, the woody stems make the flowers well-suited for use in cut flower arrangements. They will last up to a week or more in water.

Tithonias make great cut flowers

Here in San Diego, you will find them a staple nearly year-round in the fresh flower markets.

Green Mulch

Probably one of the best uses of the Mexican sunflower is as a green mulch or fertilizer for rocky and/or nutrient-depleted soils. The plant fixes nitrogen, potassium and phosphorus in its stems and foliage and releases them quickly back into the soil after the plants are cut. For this reason, many farmers will grow the plant around the edges of their fields, then “chop and drop” them into the field as a green mulch. The leaves and stems can also be tilled into the ground to provide biomass and fertilizer in marginal soils.

Reel from @Ecoversity on Instagram

Our soil here in the foothills of San Diego County is a mixture of sandy loam and rock that really benefits from fresh organic matter. So, what I do is start some tithonia seedlings in the fall and transplant them into a garden area that needs a boost in the early winter. I let the plants grow all winter, which is our wet season, so they get very bushy and green.

In early spring, a couple of weeks before I want to use that area of the garden, I will chop the tithonias to the ground and till the leaves and stems just a bit into the soil. The chopped-up material breaks down very quickly inviting soil-dwelling organisms to move in as well.

By the time I’m ready to plant in that garden, the soil is in perfect condition for a long growing season.

Growing Mexican sunflowers from seed

Like other members of the Aster family (asters, daisies, sunflowers, etc.), tithonia is easy to grow from seed. Simply plant the seed about a half-inch deep and keep the soil most (but not wet) until it sprouts (10 to 20 days).

Tithonia seedlings can be transplanted once they have their 3rd set of leaves

Once the seedling has produced its third set of leaves (usually around 4 weeks), it can be transplanted into the garden. It should start flowering in two months, give or take, depending on the weather.

You can buy tithonia seeds, but they are also really easy to harvest yourself. Just take a dried flower head and twist the crown to release the seeds from the head. (Note: the dried flowers are kind of pokey, so I use a pair of pliers to separate the seeds from the flower head.)

A tithonia flower next to dried seed heads

The tithonia flower head after the petals have fallen off

Using pliers to twist the seed cap off the flower head

Pulling apart the seed cap with pliers to separate the seeds

Pieces of the seed cap

What the seeds looks like

As long as you keep the seeds dry and out of sunlight, they will remain viable for several years.

Conclusion

So there you have it. The Mexican sunflower is a great-looking, versatile and easy to grow plant that also helps maintain and improve your garden’s soil condition. If you haven’t tried growing these, I definitely recommend them. I find them a great plant, and I bet you will too.