Mammoth Sunflowers

Asked August 3, 2013, 11:51 AM EDT

I've grown Mammoth Sunflowers every year for three years. The sunflowers are beautiful and strong and healthy. I grow lots of veggies where I grow my sunflowers and all the veggies do quite well but my sunflowers never have any seeds inside the shells. Just empty shells. What is causing this?

Benton County Oregon horticulture flowers: annuals and herbaceous perennials

4 Responses

A couple questions for you so that I can answer your question. First what is the source of the seed that you are using; do you still have the envelope that the seed was in? Second please tell me about where the sunflowers are planted and have you have seen bees on the flowers? Finally are ALL of the seeds empty and when do you check for the seeds inside the shells?

Territorial Seeds Company out of Cottage Grove, OR.

The sunflowers are located on the north side of my garden. The get sun from sun break to 9:30 am then not again until 11am but until sundown after that. All day sun with an hour and a half break. Maybe that is causing it? The bees are all over the sunflowers and seem to love them, which is why I continue to grow them.

Thank you,

oops left out one question. Yes, all the seeds pods are empty with just a small, white tissue paper of a seed in each one...I am thinking it is either the sun interruption OR not enough manure/phosphorus in soil at time of blooming. Could that be it? Everything else in the garden blooms well except the Brussell Sprouts. They have to be hit with Age Old Bloom to form big enough nodules to make it worth while. Corn does great though without that, so do beans, cukes, toms, greens, etc...

Thank you,

I have found others on the internet that describe the problem you are talking about but have yet to find a reason that it happens. I found that talks about growing and harvesting sunflowers. This talks about not harvesting until the seed head turns down and the disk on the back of the flower turns yellow. Is it possible that you are not giving them enough time to fill the shells and are harvesting too soon? Other sources say the sunflowers need lots of nutrition as do most fast growing plants. I have not found a source that would indicate a specific nutritional deficiency that would lead to no seed production in sunflowers. Our mid Willamette Valley soils generally have an abundance of phosphorus, to the point where I do not worry about adding that nutrient to my garden soils. The only way to determine if your soil is deficient is to get a soil test. The amount of sun your plants get should be sufficient based on your report. Let me know about your timing of harvest and I will continue to look for an answer.