Varieties of Helianthus are my favorite summer flowering plants. If you are not known for your green thumb, then this may soon become your favorite garden flower as well. The Mammoth Sunflower is a particularly interesting variety as it will grow over 10 feet tall with flower centers reaching over 8″ in diameter. If you are looking for a beautiful cut flower, then this variety is probably not for you. Instead, try the “Teddy Bear” variety for successful cut flower arrangements that will last.
Like all other Sunflowers, the Mammoth Sunflower is an annual that prefers full sun, is easy to grow, drought tolerant, and heat tolerant with yellow flowers that bloom in summer. It can be grown easily from seeds using a direct sowing method with a shallow planting depth of about 1 inch and requires very little maintenance or attention afterwards. The only problem that can be encountered with Mammoth Sunflowers is that they may outgrow their supports quickly. To keep these giants from falling over, stalks need to be either staked, buried deeply after seedlings emerge and begin falling over, or roots need encouragement to grow deeply on their own to support the plant. This can be done using a method of infrequent but deep watering which I have found works better than other support methods.
Although this variety is grown for interest, it is also grown commercially as well. Mammoth flowers may only be showy for a couple days (another reason why they are not excellent flowers for arrangements). However, many people take advantage of this flower’s ability to produce hundreds of edible sunflowers seeds after their flowering interest has subsided. I recommend waiting to harvest seeds until after the sunflower head droops and the backside turns yellow to brown. Seeds should be allowed to dry before being stored if not eaten immediately.