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.
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.
The short answer is that it's not too late. Consider that most ornamental and cut-flower sunflower varieties flower 60 days after planting on average. So, for most years, if seeds are planted by Aug. 15, you can enjoy these gorgeous flowers from late September to October.
Plant sunflowers in late spring, once the ground is nice and warm. Most sunflowers germinate when soil has reached 70 to 85 degrees F. The best time to plant sunflowers is just before the soil reaches this temperature.
Sunflower planting season is ideally spring or fall. In the spring, you can start seeds outside three weeks after the last frost. Those who prefer to garden indoors can sow sunflowers earlier, about two to four weeks before the weather warms up.
It's probably not too late to plant sunflowers
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.
From these examples, it's clear that if you plant late season sunflowers, it's best to find the variety with the quickest development, especially if you're expecting a light frost soon. Generally, the latest time for planting sunflowers will be in July or late August.
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.
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.
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.
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.
Sunflowers typically start blooming in August, with longer-season varieties and later-planted crops blooming into September. Peak sunflower season is late August to early September in many temperate climates.
Perennial sunflowers need a dormant period, so they do not make good winter houseplants. The growth dies in the fall, and the roots need time to rest and gear up for the next growing season. Leave landscape plants outdoors, move container-grown plants to a protected area, and wait until spring.
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.
10 to 13 weeks after planting. After two to three months, sunflowers begin to flower. Typically, sunflowers stay in bloom for three weeks, but you might get a full month if you're lucky.
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.
Sunflowers are fast reproducers, and one plant can create dozens of others. Plant seeds about an 1 inch below the ground. Germination occurs quickly, usually between 5 and 10 days, but spring crops produce more plants than summer crops. Spring crops are planted in April and May.
It's important to note that while most sunflower varieties are annuals, many will reseed themselves if left to the end of the season on their own, especially if there are critters around the planting site to help spread the seed.
After two to three months, sunflowers begin to flower. Typically, sunflowers stay in bloom for three weeks, but you might get a full month if you're lucky.
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 need full sun; see 6-8 hours of direct sunlight per day – the more the better if you are trying to grow them to their maximum potential. Choose a well-drained location, and prepare your soil by digging an area of about 2-3 feet in circumference to a depth of about 2 feet.
They do fine in soils that are slightly acidic to somewhat alkaline (pH 6.0 to 7.5). Once sunflowers get started, they can tolerate drought as befits plants whose ancestors grew happily in dry prairie regions. They are so easy to grow that they often plant themselves, springing up unbidden beneath a bird feeder.
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.
This lower threshold temperature varies with plant species. Scientists have determined the lower base temperature for sunflower is 44 °F (6.7 °C).