The giant sunflower is one of the most majestic of all flowers, reaching higher than any other flower you can imagine. Growing as tall as 20 feet (8 meters) giant sunflowers make an impressive sight seldom seen in any typical backyard. There are several varieties you may want to try your hand at growing: "Sunzilla", "Mammoth", and "California Greystripe" are popular giant varieties and, with some TLC, have the potential to attain these legendary heights! Giant sunflowers, however, can be difficult to grow - with their sheer size they require significant attention and you need to work harder to protect your giant sunflowers from the whims of nature. But despite the work involved, growing giant sunflowers is a challenge many a gardener gets excited about, either to enter into competitions or just for the sheer thrill of growing a plant as tall as a house! Growing sunflowers can also be a fun way to inspire your kids to get involved with the garden. With growth happening so quickly, changes visible even day to day, it's easy for kids to see progress in their efforts. What is the height of the tallest sunflower? According to the 2004 Guinness Book of World Records, a sunflower grown in the Netherlands holds the record for being the tallest sunflower in the world at 25 feet, 5.4 inches tall.
Growing giant sunflowers is not much different than growing regular sunflowers, but you have to focus your attention on just about every factor in the plant's life cycle to a greater degree. Giant sunflowers deplete the soil rapidly since they require so much nutrition to reach their massive heights. Each season you grow them, you will need to prepare your soil. Dig compost or manure into the planting bed to a depth of about 2 to 3 feet. Your soil will have to be loose enough for the water to be able to drain but still firm enough so that the giant sunflower will not tilt. Pay attention to weather reports - if heavy winds are called for, you may want to hold off watering until winds have tapered off. Wind is a threat especially once the sunflower head opens, since there will be a lot of weight at the top of the plant. (You do not want your sunflowers to fall over just because there is a breeze in the air!) The giant sunflower also needs even more sun than regular sunflowers, at least 7 or 8 hours a day, so you might want to ensure that the location you are planting will maximize sun exposure. Plant a giant sunflower in the shade and you can simply forget getting a giant sunflower - you will get a medium one at best.
Caring for a giant sunflower requires you to be aware of the soil conditions and water levels. The rule of thumb is to feed often and water regularly. You can feed your giant sunflowers weekly with a liquid fertilizer (such as Miracle-Grow) taking care to never pour the solution directly on the plant itself, since this can cause the stem to rot. Watering levels for the giant sunflower need to be monitored and you should keep a close eye on how much water there is left in the soil so you do not over-water. Here, the risk is not so much of rotting the roots, but that over-watering will allow the soil to loosen, making your giant sunflower tilt and potentially be uprooted. Some gardeners plant giant sunflowers next to stakes or an unshaded trellis in order to stabilize the plant, but this is not essential. If you decide to use support, tie the sunflower off in stages with thick string or growers ties - but make sure your string does not cut into the sunflower as it sways in the wind or you might end up inadvertently cutting down your plant before it reaches maturity!
The giant sunflower might be a very impressive plant to look at, but due to the sheer height and potential gangliness, some consideration needs to be given as to where you decide to plant them. Close to your house is a generally an undesired location due to the blockage of sunlight and the fact that a enormous giant sunflower next to a normal building looks, well, somewhat out of proportion. The giant sunflower will also dwarf practically every other plant or small tree in your garden. An interesting planting however, is to either plant the giant sunflower in a small grouping by an open trellis for support or simply create a wall of giant sunflowers at the end of your gardens. A wall made out of giant sunflowers is an impressive sight and although not long-lasting, the illusion of a wall will be complete for the summer months.