To learn the secret of growing sunflowers to record-breaking sizes
and heights, I turned Dr. Tom Heaton, the world's foremost
sunflower breeder and Renee 's Garden's sunflower seed
supplier. Tom has been breeding sunflowers for 30 years and has
revolutionized the market by introducing a dazzling array of new
sunflower forms and colors to the seed trade. His wholesale seed
production company specializes in long-stemmed pollenless cultivars for the cut flower market and home garden. He has developed
varieties in a full spectrum from burgundy and ruby red to orange,
peach, apricot, bright yellow, to fiery bicolors. Most of Renee's Garden
sunflower varieties are from his exuberant collection.
Fortunately for home gardeners with giant sunflower aspirations, Tom
has also focused on breeding the ultimate tall competition varieties (Renee's Garden's
"Sunzilla" ). Each year, Tom saves his longest stalk and largest
seed head of this variety in his garage to measure against the
following years. He currently prizes a 17-foot stalk and a 24 in. seed head! In this article, Tom has generously agreed to share his
method of growing giants like these in your home garden.
First -- Choose the Right Variety
Despite the growing popularity of new color introductions, the
sunflowers that grow largest are those most of us still imagine first when
thinking of sunflowers. These have tall single stalks with big flower faces of
golden yellow petals and chocolate brown centers that ripen into heavy heads
filled with seeds that birds will love.
I asked Tom why serious competitors should grow his variety instead
of traditional varieties of large sunflowers like Mammoth, Russian
Mammoth or California Greystripe. He explained that the seeds in
Sunzilla are hybrids, developed to be uniform and consistently reliable - so
that when you thin seedlings, you needn't worry that you may have
just uprooted your most potentially vigorous specimen. While older
varieties often become top-heavy and fall over in wet or windy
weather, Sunzilla has been selected for a
strong, thick stalk to support its heavy head. In ideal growing
conditions, it reaches heights of 16 feet or more and produces huge seedheads.
Dr. Tom Heaton
Renee's Giant Sunflowers:
See all Renee's Garden Sunflowers
To purchase these and other
Renee's Garden Seeds,
Site and Soil Preparation Are Critical
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.
Sunflowers are heavy feeders and deplete the soil more than many
other crops - especially if you are growing them to reach a massive height so the nutrient supply must be replenished each season.
Work in a slow release granular fertilizer - one that also contains trace
minerals-- about 8 in. deep into your soil. Tom uses Osmocote, but since I'm an organic gardener and
raise rabbits, I plan to mix in a bucketful of composted rabbit
manure plus a balanced slow-release granular fish fertilizer.
Depending on your soil, you may wish to add, in addition to
composted manure and an organic slow-release balanced fertilizer, an
organic amendment containing trace minerals such as greensand or
The Right Way to Sow and Thin For Success
To grow the largest sunflowers, it is essential to direct sow seed
directly into the garden, rather than start them in pots of any
kind. This is because sunflowers have long taproots that grow
quickly and become stunted if confined. Peat pots in particular
often dry out and block off root growth. Despite many gardener's
best intentions, transplanting often gets postponed - so beat the odds
and plan to sow seeds in the ground.
Since sunflowers that are planted in midsummer often flower on
shorter stalks, sow your giant sunflowers earlier-as soon as all
danger of frost is past and night temperatures are above 50 degrees
Fahrenheit both day and night. In the shorter-season, cold winter
areas of the U.S., this means late May to early June.
The ideal spacing in rows for giant sunflowers with large seed heads
is 20 in. apart. If you plant closer, you might get taller stalks but
smaller heads. If you plant farther apart, the seed head may be
larger, but possibly too heavy for the stalk to bear. If you have
limited space, Tom recommends sowing in a small clump that will
eventually be thinned to one plant.
To sow seeds, water your soil, and press seeds 1 inch deep in clumps of
5-6 seeds about 6-8 in. apart. Put snail bait in a circle around the
clump (I like the product Sluggo because it is non-toxic to humans,
pets and wildlife), and cover loosely with netting to protect emerging seedlings
from birds. If the soil is kept moist, seedlings will appear within
When the plants grow to 3 inches, thin them to the most vigorous 3 or 4.
When they are a foot tall, thin them to 2, and when they reach 2
feet high, select the best, most vigorous candidate. The point of
this gradual thinning method is to ensure that you're left with at
least one good seedling in the event that predators damage any of
the others. Remember, it's critical to thin back to the best single
seedling if you're going for giant sunflowers. Leaving even several
seedlings growing too close together will keep you from growing a
giant in your garden.
Feeding and Care of Your Growing Giant
Feed often and water regularly. While the plant is small, water around the root zone, about 3-4
from the plant with about 2 gallons of properly diluted
liquid fertilizer solution per week. For larger plants, scrape out a small doughnut-shaped
moat about 18 inches around the plant and about four inches deep.
Pour several gallons of properly diluted fertilizer into the moat
every week. Sunflower roots can grow to 4 feet below the soil
surface. Avoid pouring fertilizer directly on the stems, since this can
cause them to rot.
Another feeding method for larger plants is to make several
holes by driving a steel stake into the ground about 3-4 feet deep
and about 1½ feet from the plant. Fill the holes with properly
diluted liquid fertilizer. Tom uses Miracle Grow or Schulz's growing
solution, but as an organic gardener, you can use properly diluted
fish emulsion or other liquid organic fertilizers.
Tom recommends that you care for giant sunflowers as members of your
family. Be attentive to weather reports, especially, as your plants
become taller and more top-heavy. When heavy winds are predicted,
delay watering to reduce their chances of blowing over. Staking
isn't usually necessary for sunflowers, but it can be helpful in
extremely windy areas or if they must be grown in conditions that
are too crowded or in too much shade.
Harvesting and Enjoying Giant Seed heads
As the petals fall off, the center florets dry up and the seed
kernels begin to swell in the disks, carefully climb a stepladder
and cover your flower head with a mesh onion bag or loose burlap or
paper bag. This keeps marauding birds from robbing your seeds so
that the heads look perfect and complete when you are ready to show
them off to friends or proudly display them on their long stalks at
your local county fair. Cut the stalks at the base when the ripened
seeds develop a hard shell. If you plan to preserve them for your bird feeder, wait until the seeds are
completely dry; then remove them by hand or by rubbing them over
wire mesh into a basket. Store in tightly closed containers to keep
Giant Fun for All Ages
Growing giant Sunzilla sunflowers is a great way for getting
children inspired to enjoy the garden. The seeds, which make tasty
snacks for songbirds, are large and easy to handle. Like
Jack's beanstalk, the plants grow quickly skyward, and the flower
heads look cheerful and lion-like. Tall sunflowers can be planted in
formation: as forests, playhouses or teepees. You can even grow
colorful vines like scarlet runner beans up the stalks if you give
the sunflowers several weeks head start. It's easy to get children
involved in the excitement of watching how tall a family sunflower
grows each day, or let them compete on their own! I plan to give
seeds to several neighbors, and compare stalks at the end of the