If you live in a warm climate where the first frost comes well into late fall, you can plant sunflowers even later in the season. Be sure to choose the right variety for the time you still have left and follow our growing tips to make sure your sunflowers look marvelous come harvest season.
Annual sunflowers bloom during summer and into autumn. Sow new plants every few weeks and you'll enjoy non-stop flowers until the first frost. Perennial sunflowers bloom for a period of 8-12 weeks with some beginning as early as July and others finishing as late as October.
Sunflowers should be planted 1 to 1½ inches deep and about 6 inches apart after the soil has thoroughly warmed. If you wish, you can plant multiple seeds and thin them to the strongest contenders when the plants are six inches tall. Give plants plenty of room, especially for low-growing varieties that will branch out.
After pollination and petal drop, sunflower can withstand temperatures as low as 25 F with only minor damage. Twenty-five degree temperatures at the bud stage will often damage leaf and stalk below the bud and seeds will not develop. Easily damaged by light frosts in 28-32F range.
It may be towards the end of summer, but you can still plant sunflowers and enjoy them during the fall. In north Florida, try to complete sunflower planting by the third week in August. Depending on the variety, sunflowers will bloom about 55 to 75 days after planting – 60 days is a good average.
So how late can you plant sunflower seeds? With varieties that only require a 50-60 day growing season, you should be able to plant sunflowers as late as July for fall flowers. If you live in a warm climate where the first frost comes well into late fall, you can plant sunflowers even later in the season.
While it's not recommended to plant sunflower seeds in late summer or fall due to colder temperatures and shorter days, some varieties may still thrive during this time. However, choosing these varieties carefully is important, and taking additional steps to ensure their success.
Twenty-five degrees Fahrenheit at the bud stage will often damage the stalk below the bud and seeds will not develop. If hard frosts do occur, many times only the seed in the center of the head (the last to pollinate) will be affected."
How long do sunflowers take to grow? There are various varieties of sunflowers, and each one will grow at a different rate. On average, though, it takes between 80 and 120 days for a plant to mature and develop seeds.
If soil temperatures are just right, sunflower seedlings will sprout up in 10 to 14 days. Growing sunflower seeds requires space. To start sunflowers indoors, plant three seeds per each 3- to 4-inch peat pot. A soilless planting media will give you the best drainage.
Sunflowers are generally planted in spring or early summer for late summer and fall blooming. However, if you live in a warmer climate, you can get a second planting in for mid and late fall flowers. Late season sunflowers may grow a little shorter or produce fewer flowers because there will be fewer daylight hours.
Sunflowers bloom last only till the middle of fall and it is highly unlikely to get your hands on these pretty flowers in December. If the sunflowers are late bloomers, you might still get some till October. But after October, it becomes difficult for these summer and sun-loving plants to produce flowers.
Many flowers carry the name “sunflower” that are, in fact, completely different species of plants. Some sunflowers are annual and survive only one season, and others are perennials that will return every year. All perennial and annual sunflowers produce brilliant flowers that are a highlight of any late-summer garden.
At the end of the season, it's easy to harvest sunflower seeds to dry for re-planting, baking up for a tasty snack, and re-purposing into suet cakes to feed the birds in the winter months. Sunflowers are ready to harvest when their foliage turns yellow, the petals die down and the seeds look plump.
The allelopathic characteristics of sunflowers are toxic to some plants, potatoes being one of them. This process inhibits germination and can stunt the growth of potatoes. They also compete for nutrients in the soil. Potatoes should be planted well away from sunflowers to avoid them affecting one another.
Place one seed in the divot and cover it with soil. If you have extra seeds, you can put 2-3 in one hole and then trim off the two weaker seedlings. Water the soil gently to help settle it. Sunflower seeds of most varieties should be planted about 18-24 inches apart, as they will grow to be quite large.
When to Plant Sunflowers. Plant seeds after the danger of spring frost has passed and the soil temperature is at least 60 degrees. This will be between March and May, depending on where you live.
Newly planted sunflowers need damp conditions, especially during germination, but established sunflower plants need about one inch of water per week. Underwatered sunflowers will not grow large or bloom, and the plants may droop and appear wilted. Overwatered sunflowers are susceptible to root rot.
There are pint-sized sunflowers that grow just a foot tall and giant varieties that reach for the sky, but you don't need a big garden to grow sunflowers. These classic summer bloomers can be planted in plastic pots, fabric planters, or even buckets.
Sunflowers that have reached the R7 stage can withstand temperatures down to 25 °F (-4 °C) with only minor damage. Only a frost duration of 6 hours or more below 25 °F would penetrate the thick layer on the back of the sunflower head and cause damage.
Best Fertilizer For Sunflower
Feed sunflowers using a balanced formula with a ratio of 10-10-10 or a product low in nitrogen with a 5-10-10 NPK ratio. A balanced fertilizer will support the entire plant. Nitrogen supports heavy foliage growth, and nitrogen-rich fertilizers are a good choice for leafy plants.
Yes, old seeds may produce less vigorous plants. Seeds that are just a couple years old should still grow to become perfectly robust plants, but as seeds get really old, both the germination rate and plant vigor can decline.
One of the fastest flowering varieties, 'Ruby Eclipse' (pictured above, right) is an attractive branching sunflower that's as productive as it is beautiful. Blooms are a mix of bicolor flowers in shades of cream, dusty rose, and ruby-red. Super easy to grow, with one planting producing for 3 weeks.