Tithonia

( tith - OH - nee - uh )

At-A-Glance Information

The plants in this genus, commonly called Mexican Sunflowers, need full sun and regular water, and their flowers will attract hummingbirds and butterflies to your garden. Leaves are green and velvety, and flowers range in color from yellow to orange-scarlet with centers of yellow. They are native to Mexico and Central America, and are great when used as a temporary screening plant. These plants can take heat and some drought conditions.

Tithonia Species and Varietals

The genus Tithonia is a member of the plant family Asteraceae and includes 12 species. Mexican Sunflower grows in all zones (to find your zone, click here: Zone Map).

Tithonia diversifolia (Tree Marigold, Mexican Tournesol, Mexican Sunflower, Japanese Sunflower, Nitobe Chrysanthemum)
These plants are native to Mexico and Central America, and is an introduced species in many other areas of the world. Plants can be either annual or perennial, depending on the climate they are grown in. Individuals reach up to 10 feet tall with upright stalks topped with showy, honey scented flowers. Blooms are golden yellow with yellow centers.

Tithonia rotundifolia (Tithonia speciosa) (Red Sunflower, Mexican Sunflower)
Native to warmer, moist regions in North America, these plants produce vermillion-colored flowers with yellow centers. They are typically used as hedges behind smaller plants. Foliage is green. Varieties include 'Aztec Sun' (with apricot-gold flowers on a 4 foot tall plant), 'Fiesta del Sol' (with orange flowers on a 2.5 foot tall plant), and Goldfinger (a bushy 4 foot tall plant with deep orange blooms).

Caring for Tithonia

Sow Tithonia seeds in place in springtime. These plants are also sometimes available for purchase through reputable nurseries. They appreciate a spot in the garden that receives full sun; they do not tolerate shade well, becoming floppy and suffering from fungal diseases more often than those grown in sun. They like lean to moderately fertile soils that are well-draining and have a pH of between 6.0 and 7.0 (slightly acidic to neutral), and do well in rocky and sandy soils. If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home. At maturity, Tithonia plants are considered to be very drought tolerant, even thriving with some neglect. They do not tolerate wet soil well, so it is critical to not overwater.

Fertilizing the soil beneath Tithonia plants is not necessary; they actually do better in leaner soils. Prune to remove spent flowering heads (unless you will be collecting seeds for propagation). It is not necessary to do too much pruning, as these sunflowers are best left alone. However, they can sometimes get a bit lanky (especially if grown in too much shade), and can handle rejuvenation prunings. During lulls in blooming, cut back 1/3 of the top of the plant to refresh and tidy it up.

Propagation

Tithonia, or Mexican Sunflower, can be propagated by cutting or seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant, especially if you are propagating a hybrid cultivar. To propagate your Mexican Sunflowers, follow the instructions below:

Propagating Physostegia by Seed

Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand. You will also, after a few weeks, need individual 3-inch pots for each seedling that grows.
Harvest your seeds. The seed heads on plants are pretty easy to spot, they're left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will continue to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
Physostegia seeds will need a period of cold-stratification in order to germinate. To complete this process, first place seeds in a bag or other sealable container filled with moistened sand or peat moss. Then, place the container in the refrigerator (or similarly cool, dark space) for 2-3 months. The ideal temperature for cold-stratification is around 40 degrees Fahrenheit. After this period has passed, remove seeds from the container.
Get your container prepared. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 1-2 weeks from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 65 and 72 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.

Propagating Physostegia by Cutting

Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. If you don't have any potting medium on hand, you can make some. Just mix together equal parts (by volume) moss peat and horticultural-grade sand or grit sand.
In early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 3-4 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer; typically they will need daily watering. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new plant.