Ask a Master Gardener: Growing sunflowers | Home And Garden

Question: Each year I try to grow something new and different in my garden. This year, I have decided to grow sunflowers. Looking through an Oregon-based seed catalog, I noticed that there are over a dozen varieties that will grow locally. Not only will sunflowers be a beautiful addition to my garden, but I am also hoping to harvest the seeds for my bird feeder. What advice can you offer me so I will have success?

Answer: Years ago, when one thought of sunflowers, the image was of a tall, straight, 6 foot stalk with one very large, brilliant yellow, seedy head. There were no variations.

However, over the years, new varieties have been developed, and now gardeners can chose from a variety of flower colors, flower head shapes and heights.

Sunflowers are in the plant genus Helianthus annuus and include about 70 species in the Asteraceae family. The genus name comes from the Greek words “helios” meaning sun and “anthos” meaning flower.

Sunflowers are an annual that grow in Zones 2-11 across the United States. They bloom from July to August. They are drought tolerant and easy to maintain once established. Sunflowers require full sun.

They grow best in well-drained soils; however, they are tolerant of other soil types. Sunflowers do best when grown in slightly acidic soil with a pH from 6.0 to 6.8. An application of a balanced fertilizer, such as 10-10-10, is needed at planting time and again four weeks later.

Sunflowers are one of the easiest flowers to start from seed. The seed is large and easily handled, and you can direct seed into the garden, or germinate indoors and plant in the garden once true leaves have formed.

If you decide to direct seed, wait a few weeks after all danger of frost has passed. In Douglas County, that is April 3. Also wait until the soil temperature warms up to 60 degrees. Plant the seeds 1 inch deep. For varieties that are 2-5 feet tall, leave about 6 inches between them. Space taller sunflowers at least 1 foot apart and giant sunflowers 2 feet apart.

The seeds will start to germinate within 7-10 days. Water the sunflower seeds lightly for the first seven to 10 days to ensure strong germination. After germination, watering can be reduced to a couple of times a week.

If you decide to start the seeds indoors, make sure you use biodegradable containers. This will allow you to plant the entire pot without disturbing the seedling roots. Remove any part of the container that sticks above the soil surface because it will act like a wick and dry out the roots.

You can have sunflowers blooming all season long through succession planting. There are two easy ways of doing this. You can plant multiple varieties that have different days to maturity all at one time or you can plant the same variety at one to two week intervals.

The taller varieties should be planted in an area that is protected from strong winds. If this isn’t possible, then you will want to stake them.

If you want to harvest the sunflower seed for food, you may have to contend with aerial attacks from birds. Scarecrows, shiny spinning pans, a net to protect the seed heads or an owl decoy may be effective in deterring pesky birds until it’s time to harvest.

When selecting what variety to grow, read the seed description carefully to determine if the variety is meant for human consumption or for bird seed.

Sunflowers are ready to harvest when the heads begin to droop over and dry out. To harvest the seeds ahead of the birds, cut off seed heads with a foot or so of stem attached and hang them in a warm, dry place that is well-ventilated and protected from rodents and insects. Keep the harvested seed heads in a dry spot to prevent mold and let them cure for several weeks.

When the seeds are thoroughly dried, dislodge them by rubbing two heads together or by brushing them with your fingers or a stiff brush. Allow the seeds to dry for a few more days in airtight jars in the refrigerator to retain flavor.

One interesting fact about sunflowers is that the flower heads tend to follow the path of the sun each day from morning to night. The sunflower heads will turn east to west as the day goes on and then rotate back east during the night to start over again.

This process, called heliotropism, allows the growing leaves and immature flowers to absorb 10-15{28ab41d673507bfe0daf970418d2e81f9476b3e139564442359ad7402c370b16} more sunlight for photosynthesis than if they were sitting still. However, as the flower bud matures and blossoms, the stem stiffens and the flower becomes fixed facing the eastward direction.

Another interesting fact about sunflowers is that their hulls have a toxin that prevents the growth of other plants. You might have noticed that soil is often bare under bird feeders when sunflower hulls accumulate on the ground. This is called allopathy. Remove the hulls regularly or put the feeder where there is no danger of damage to lawns or other desirable vegetation.

Good luck with your sunflowers. They are both a beautiful and useful addition in any garden.