Sunflower Plants Growing Multiple Flowers Instead or One?

Question:

I have been growing sunflowers for a few years. The first two years I planted them, I had great success. I had tall sunflowers with the large heads and many seeds to eat. But the last few years I can't get those large heads anymore. The sunflowers grow tall and then the tops of the plant branch off and make several small flowers rather than one big one. I am buying new seeds every year. This year I chose Mammoth. What am I doing wrong?

Hardiness Zone: 7a

Monica from Moab, UT

Answer:

Monica,There are a couple of reasons you could be seeing multiple heads on your sunflowers. The first is pest damage. The larvae of certain sunflower pests may not always be visible (especially on tall varieties) because the larvae are tiny and they feed on developing seeds and heads. Damage often results in shrunken or malformed (sometimes multiple) heads. The larvae of sunflower seed weevils and sunflower midges are the primary culprits. The larvae over winter in the soil. Tilling in the fall and again in the spring and practicing crop rotation will help minimize infestations.

Herbicide drift or chemical residue in the soil is another common cause of multiple heads on sunflowers. Herbicides drifting over from other parts of the garden (or the neighbor's garden) can cause abnormal bending or twisting of stems and/or leaf petioles, slow growth, or cause the development of multiple heads. This happened to my neighbor this year. In her case, she didn't actually plant them, the birds and squirrels feeding at my bird feeders did. When sunflowers sprouted in her backyard she decided to leave them alone. As they grew, they developed multiple heads. The seeds carried to her yard from my feeders were black oil sunflower seeds.

I imagine they were harvested from commercially grown sunflower crops that were grown in large fields. Even if these fields were not treated with herbicides, crops in nearby fields may have been. Meanwhile, a few weeks later and a mere 25 yards away, the mammoth sunflowers planted in my garden bloomed normally-none of them developed multiple heads. Could her multiple heads could have been herbicide drift? Maybe. Neither of us uses chemicals on our yards or gardens so it would have to have been the seeds. It remains a mystery.

Sunflowers are native to North America. In the wild they usually have multiple heads-up to 20 heads per flower is the norm. These wild seeds make up the genetic basis for the domesticated and hybrid seeds we see today. Could yours be cross-pollinating with nearby wild sunflowers? It's just another possibility.

Ellen