At winter's end, gardeners rush to the seed aisle of the garden center, looking for something fast-growing that will transform the landscape in a few months, much like the annual Mexican sunflower (Tithonia rotundifolia) that quickly leaps to shoulder-height and beyond when temperatures heat up.
Mexican sunflowers yield dozens of showy daisy-like blooms with petals in fiery colors of red, orange, or yellow, all with yellow centers. The serrated ovate leaves are dark green on tall, sturdy stems. Plant seeds or seedlings in the spring to enjoy an ongoing display of profuse blooms throughout the summer into fall.
|Botanical Name||Tithonia rotundifolia|
|Common Name||Mexican Sunflower, tree marigold|
|Plant Type||Annual, perennial|
|Mature Size||3-8 ft. tall|
|Soil Type||Sandy, well-drained|
|Bloom Time||Summer, fall|
|Flower Color||Yellow, orange|
|Hardiness Zones||9-11 (USDA)|
|Native Area||North America, Central America|
Mexican Sunflower Care
Mexican sunflowers are ideal for the beginner gardener who wants pops of color to fill in a large blank spot in the flower border. They're also great for cut flower arrangements while producing enough to attract scores of butterflies and beneficial insects like parasitic wasps. These flowers aren’t fussy about soil and don’t need much care after they start growing.
These annuals are a welcome addition to the butterfly garden thanks to their nectar-rich shallow blossoms that meet a pollinator’s needs. Unlike many butterfly-friendly plants that are small in stature, the tall blooms of the Mexican sunflower bring butterflies right up to eye level, making them easier to observe. A mature stand of sunflowers makes a good addition to the vegetable garden, as the pollinators they attract will help increase your vegetable yields.
One packet of Mexican sunflowers will give you many vasefuls of cut flowers throughout the summer. Plant them with companions that thrive in the same sunny site and average soil, like cosmos and zinnias, which will also act as cut-and-come-again blooms for the cutting garden.
Full sun is a critical factor in growing healthy Mexican sunflowers. Plants growing in shady areas may not bloom, will flop over, and might suffer from fungal diseases.
Save your soil amendments for fussier flowers like roses and dahlias, because Mexican sunflowers like lean soils with low nutrient content. Good drainage is important to prevent problems like root rot. Sandy or rocky soils more closely resemble the native soils of Mexico where the plants grow wild.
Mexican sunflowers are drought tolerant throughout their life cycle and don't need watering, contributing to their low-maintenance charm. Wet soil is not tolerated by Mexican sunflowers, but if your area gets more rain than average, you can compensate for this by planting them in soil with excellent drainage.
Temperature and Humidity
Mexican sunflowers love hot weather, even days with triple-digit temperatures. Conversely, cool weather stops the Mexican sunflower in its tracks. When nighttime temperatures are in the 60s, it’s the right time to grow Mexican sunflowers. Average humidity is best for healthy plants. Provide extra spacing for plants in humid areas to prevent powdery mildew.
Mexican sunflowers grow just fine without any supplemental fertilizer. In areas with especially depleted soils, you can add an all-purpose flower fertilizer at the beginning of the season to get plants off to a quick start. For the amount, follow the product label instructions.
Types of Mexican Sunflowers
- ‘Torch’ is the mainstay of Mexican sunflowers, growing in gardens since the 1950s.
- ‘Fiesta del Sol’ is a dwarf variety for smaller gardens or containers, growing between 2 and 3 feet in height.
- ‘Goldfinger’ is another good dwarf variety.
Pruning Mexican sunflowers isn’t necessary but can help to get lanky plants under control or to keep overgrown plants in bounds. Keep in mind that you may sacrifice some blooms when pruning. Cut off the top 1/3 of the plant when it’s experiencing a lull in blooming to both deadhead and tidy the plant.
Propagating Mexican Sunflowers
Although the Mexican sunflower is easy to grow from seed, if you can’t find your favorite variety you can also propagate plants by stem cuttings. Unlike established Mexican sunflowers, this type of propagation requires daily watering to get the cuttings to root. Here's how it's done:
- Take two or three stem pieces and cut them down with sharp pruners to about 12 inches tall.
- Remove all but one pair of leaves on the stem. Cut the remaining leaves in half, as they are too large to be supported by the cutting.
- For each cutting, fill a 4-inch pot (plastic, clay, or terra cotta) with large drain holes with loose potting medium. Water until the soil is moist.
- Insert about 6 inches of the stem into the soil and gently press down the soil around the stem.
- Keep the pots in a location with filtered sun and water daily. Expect roots to form in about 10 days.
- Transplant outdoors in about eight weeks, or when they have developed a strong root system and the roots start to grow out of the pot's drain holes.
How to Grow Mexican Sunflowers From Seed
The small, triangular seeds of Mexican sunflower germinate easily in warm, moist soil. The quickest approach is to sow the seeds outdoors, at the same time you plant tomatoes, two weeks after the last frost. In short summer areas, zone 4 and colder, start the seeds indoors six weeks before the last frost to ensure the plants have time to mature and bloom before fall.
Because of its large size and rapid growth, plant no more than a few Mexican sunflower seeds in a container. Sow seeds directly in the pot, as large plants are difficult to transplant. Use a soilless potting mix with good drainage.
Potting and Repotting Mexican Sunflowers
You can also grow dwarf varieties of Mexican sunflowers in pots on your patio, deck, or balcony. Like for all patio plants, breathable clay or terra cotta pots with large drain holes are the best choice because they keep the soil cooler than plastic pots and ensure evaporation.
Because Mexican sunflowers are annuals in most zones, choose a pot that will fit the mature plant without requiring any repotting during their single-season lifespan. A gallon-pot is a good size for one sunflower. Plant it in the center of the pot. Mexican sunflowers are also attractive in larger planters with trailing plants like million bells or portulaca, which also appreciate full sun and dry conditions.
Mexican sunflower doesn't survive the winter outside of its native range. Count on starting new plants in the spring.
Common Pests and Plant Diseases
Snails and slugs sometimes bother Mexican sunflowers, especially in rainy weather. Place a piece of damp cardboard beside plants and collect the pests when they hide during daylight hours. The plants might suffer from fungal diseases if the area is too shady, and they might suffer from powdery mildew if they are too crowded, especially in humid areas.
How to Get Mexican Sunflowers to Bloom
Unlike other plants, Mexican sunflowers thrive in rocky or sandy soil. In fact, you might get better blooms from poor soil than you will from robust, nutrient-rich soil. Sun is also a factor, as these plants need a lot of it. If they still aren't blooming, consider that they might have too much water sitting around the roots; the soil must be well-draining.
What is the difference between sunflowers and Mexican sunflowers?
Mexican sunflowers and common sunflowers (Helianthus annuus) are both tall, sun-loving annual flowers that tolerate dry and poor soils. Common sunflowers usually have larger blooms, sometimes larger than 12 inches in diameter, and many varieties also have edible seeds. Grow the two sunflower plants at the back of the border for a visual and pollinator feast.
What do I do with Mexican sunflowers at the end of the season?
These flowers provide excellent nutrients to the garden. Cut them down, chop up the stalks, and add them to your compost bin.
Can Mexican sunflowers grow indoors?
Though you might try dwarf varieties as container plants, these need to be kept outside so they get the proper sunlight and high temperatures they need to thrive.