How far apart to plant sunflowers is an important choice and depends on the purpose you’re growing the sunflowers for and the type of sunflowers you’re growing.
If you’re growing flowers to harvest as cut flowers and place in vases you’ll want to plant sunflowers pretty close together to keep their stems from becoming too thick and not fitting well in flower arrangements.
Some types of sunflowers are bushier than others. Knowing about the variety you’re growing is necessary to space sunflowers correctly. You should go by the instructions for the specific variety you’re growing but here are some general guidelines.
Branching type sunflowers need plenty of space, especially the larger ones like Skyscraper and other giant sunflower varieties. Plant these 24-36″ apart in all directions. Tall single stem sunflowers can be planted 12-24″ apart and dwarf sunflowers can be planted 6-12″ apart.
This is a branching type sunflower also sometimes called a multi-headed sunflower. They have a wider spread than single stem sunflowers and need more space.
The University of Minnesota Extension recommends planting varieties that are between 2-5′ tall 6″ apart, taller sunflowers 1′ apart, and giant sunflowers 2′ apart. Taller sunflowers are something like 5-10′ feet tall and giant sunflowers over 10′ tall.
Sunflower Plant Spacing vs. Yields
Here are two quotes from a study on sunflower spacing done in India in 1975.
These studies have shown that sunflowers can be manipulated over a wide range of plant populations and row spacings without seriously affecting yield.-EFFECTS OF PLANT POPULATION AND ROW SPACING ON SUNFLOWER AGRONOMY
Populations of 60,000 to 75,000 plants/ha at row spacings of 35-60 cm are recommended for sunflower production under dryland conditions.-EFFECTS OF PLANT POPULATION AND ROW SPACING ON SUNFLOWER AGRONOMY
Dryland conditions means without supplemental irrigation. Plants with irrigation could be planted closer together because each plant would have more access to water.
The spacing recommended equals 1 sunflower plant per 1.8 square foot to 1.4 square foot.
This study was conducted by the University of Wisconsin’s Agriculture Department. In Table 2 the results of the experiments are listed.
The lowest plant density was 14,970 flower heads per acre, 1 plant per 2.9 square feet, and the highest plant density was 34,800 sunflower heads per acre, 1 plant per 1.25 square feet.
The seed yield increased from from 2,004 lbs. to 2,232 lbs. per acre. The yield increased only 10% even though the plant density doubled.
What Happens If You Plant Sunflowers Too Close Together?
Planting sunflowers too close together won’t cause too much of a problem. Sunflower heads will be smaller and stalks will be thinner at tighter spacings. In the most extreme case some sunflower plants might not produce flowers.
The plants would be competing for sunlight, water, and nutrients and at a very tight spacing some sunflower plants might not be able to get all they need to produce a flower head.
I’ve never seen this happen but this is how it works for all plants. Corn is a good example. Corn is planted with a high plant density so that one corn plant will typically only grow one ear per plant. Farmers grow varieties of corn that do well in high plant densities.
However, you will usually be able to find corn plants on the edges of fields that have multiple ears due to their increased access to sunlight, water, and nutrients. Corn planted too close together some plants might not produce any ears of corn.
How Much Space Does a Sunflower Plant Need?
In practice with square foot gardening methods plant one sunflower per square foot. For the best results follow the spacing guidelines for the specific variety of sunflower you’re growing.
Square foot gardening is an intensive gardening method usually used in raised bed gardening. Intensive gardening is trying to get as many plants as possible into the space that you have so the spacing guidelines are on the tighter side of most spacing recommendations.
Square foot gardeners commonly divide their beds into actual square foot sections. The bed above has wood trim separating beds but also commonly used is wire paneling or irrigation hose.
How Far Apart To Plant Mammoth Flowers?
Mammoth sunflowers and other giant type sunflowers should be planted about 18-24″ apart. These sunflowers have large heads that reach around 10″ in diameter so they need at least that much space to themselves.
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