Dahlias are one of my favorite flowers to grow and to photograph. I grow Dahlias in my greenhouse and in front of my darkroom and outside my greenhouse in planters too.
With so many different colors and varieties, I never tire of them. I think they are elegant, interesting, and beautiful.
Did you know that each floret is actually a flower and not a petal?
The Aztecs used the long hollow stems of Dahlias to store water and they ate the flowers and tubers.
Dahlias are annual blooming plants, with mostly tuberous roots. While some have herbaceous stems, others have stems which lignify in the absence of secondary tissue and re-sprout following winter dormancy, allowing further seasons of growth. As a member of the Asteraceae the flower head is actually a composite (hence the older name Compositae) with both central disc florets and surrounding ray florets.
Each floret is a flower in its own right, but is often incorrectly described as a petal, particularly by horticulturists.
The modern name Asteraceae refers to the appearance of a star with surrounding rays.
In the language of flowers, Dahlias represent dignity and stability, as well as meaning my gratitude exceeds your care.
EARLY HISTORY OF DAHLIA FLOWERS
Spaniards reported finding Dahlias growing in Mexico in 1525, but the earliest known description is by Francisco Hernández, physician to Philip II, who was ordered to visit Mexico in 1570 to study the "natural products of that country".
They were used as a source of food by the indigenous peoples, and were both gathered in the wild and cultivated. Yes, you can eat them and I think they taste like a potato mixed with a radish.
The Aztecs used them to treat epilepsy and employed the long hollow stem of the (Dahlia imperalis) for water pipes. The indigenous peoples variously identified the plants as "Chichipatl" (Toltecs) and "Acocotle" or "Cocoxochitl" (Aztecs). From Hernandez' perception of Aztec, to Spanish, through various other translations, the word is "water cane", "water pipe", "water pipe flower", "hollow stem flower" and "cane flower". All these refer to the hollowness of the plants' stem.
Hernandez described two varieties of dahlias (the pinwheel-like Dahlia pinnata and the huge Dahlia imperialis) as well as other medicinal plants of New Spain. Francisco Dominguez, a Hidalgo gentleman who accompanied Hernandez on part of his seven-year study, made a series of drawings to supplement the four volume report. Three of his drawings showed plants with flowers: two resembled the modern bedding dahlia, and one resembled the species Dahlia merki; all displayed a high degree of doubleness.
In 1578 the manuscript, entitled Nova Plantarum, Animalium et Mineralium Mexicanorum Historia, was sent back to the Escorial in Madrid; they were not translated into Latin by Francisco Ximenes until 1615. In 1640, Francisco Cesi, President of the Academia Linei of Rome, bought the Ximenes translation, and after annotating it, published it in 1649-1651 in two volumes as Rerum Medicarum Novae Hispaniae Thesaurus Seu Nova Plantarium, Animalium et Mineraliuím Mexicanorum Historia. The original manuscripts were destroyed in a fire in the mid-1600s.
PLANTING DAHLIA FLOWERS
Dahlias are colorful flowers which are planted in the spring and generally bloom midsummer to the first frost, when many other flowers are long past their best.
Dahlias are known as tuberous-rooted perennials which grow from small brown tubers. They come in a rainbow of colors and range in size from giant 10-inch "dinner plates" to small 2-inch lollipop-style pompons. Most dahlias grow to be 4 to 5 feet tall. Dahlias are not well suited to extreme temperatures, and they require more water than many other flowers, but they like to be in full sun.
- Dahlias will struggle in cold soil, so wait until all danger of spring frost is past before planting. (I plant them a little after the tomato plants go in.)
- Select a planting site with full sun. Dahlias grow more blooms with 6 to 8 hours of direct sunlight. They love the morning sunlight best. Choose a location with a bit of protection from the wind.
- Dahlias thrive in rich, well-drained soil. The pH level of your soil should be 6.5-7.0, slightly acidic.If you have a heavier soil, add in sand, peat moss or aged manure to lighten and loosen the soil texture for better drainage.
- Bedding dahlias can be planted 9 to 12 inches apart. The smaller flowering types, which are usually about 3 feet tall, should be spaced 2 feet apart. The taller, larger-flowered dahlias should be spaced 3 feet apart. If you plant dahlias about 1 foot apart, they make a nice flowering hedge and will support each other.
- The planting hole should be slightly larger than the root ball of the plant and incorporate some compost or sphagnum peat moss into the soil. It also helps to mix a handful of bonemeal into the planting hole. Otherwise, do not fertilize at planting.
- Avoid dahlia tubers that appear wrinkled or rotten. Pink “eyes” (buds) or a little bit of green growth are good signs. Don’t break or cut individual dahlia tubers as you would potatoes.
- Dig a hole that’s about 6 to 8 inches deep. Set the tubers into it, with the growing points, or “eyes,” facing up, and cover with 2 to 3 inches of soil (some say 1 inch is adequate). As the stem sprouts, fill in with soil until it is at ground level.
- Tall, large-flowered cultivars will require support. Place stakes (five to six feet tall) around plants at planting time and tie stems to them as the plants grow.
- Large dahlias and those grown solely for cut flowers are best grown in a dedicated plot in rows on their own, free from competition from other plants. Dahlias of medium to low height mix well with other summer flowers. If you only have a vegetable garden, it’s the perfect place to put a row of dahlias for cutting (and something to look at while you’re weeding!).
- Medium to dwarf-size dahlias will do well in containers.
- Dahlias start blooming about 8 weeks after planting, starting in mid-July.
- Some gardeners start tubers indoors in containers a month ahead to get a jump on the season.
- Do not water the tubers right after planting; this encourages rot. Wait until the sprouts have appeared above the soil to water.
- Do not bother mulching the plants. The mulch harbors slugs and dahlias like the sun on their roots.
- Apply slug and snail bait to avoid garden pests.
CARING FOR DAHLIA FLOWERS
- Don't water the soil until the dahlia plants appear; in fact, overwatering can cause tubers to rot. After dahlias are established, provide a deep watering 2 to 3 times a week for at least 30 minutes with a sprinkler (and more in dry, hot climates).
- Dahlias benefit from a low-nitrogen liquid fertilizer (similar to what you would use for vegetables) such as a 5-10-10 or 10-20-20. Fertilize after sprouting and then every 3 to 4 weeks from mid-summer until early Autumn. Do NOT over fertilize, especially with nitrogen, or you risk small/no blooms, weak tubers, or rot.
- Like many large-flower hybrid plants, the big dahlias may need extra attention before or after rain, when open blooms tend to fill up with water or take a beating from the wind.
- When plants are about 1 foot tall pinch out 3-4 inches of the growing center branch to encourage bushier plants and to increase stem count and stem length.
- If you want to grow large flowers try disbudding—removing the 2 smaller buds next to the central one in the flower cluster. This allows the plant to put all of its energy into fewer but considerably larger flowers.
- Bedding dahlias need no staking or disbudding; simply pinch out the growing point to encourage bushiness, and deadhead as the flowers fade. Pinch the center shoot just above the third set of leaves.
- For the taller dahlias, insert stakes at planting time. Moderately pinch, disbranch, and disbud, and deadhead to produce a showy display for 3 months or more.
- Dahlia foliage blackens with the first frost.
- Dahlias are hardy to Zone 8 and can be cut back and left in the ground to overwinter; cover with a deep, dry mulch. Further north, the tuberous roots should be lifted and stored during the winter. (Some dahlias will survive in Zone 7 if the winter isn’t too severe.)
PESTS & DISEASES
- Slugs and snails: Bait 2 weeks after planting and continue to bait throughout the season.
- Mites: To avoid spider mites, spray beginning in late July and continue to spray through September. Speak to your garden center about recommended sprays for your area.
- Earwigs and Cucumber Beetle: They can eat the petals though they do not hurt the plant itself.
- Deer: Find a list of deer-resistant plants to grow around your dahlias.
- Powdery Mildew: This commonly shows up in the fall. You can preventatively spray before this issue arises from late July to August.