How to Grow Sunflowers

Watering: If you're able to water your sunflowers, note that they prefer more water than other flowers when they are young to help them grow fast and strong. Keep young seedlings well-watered to prevent wilting and stunting. Add 2 gallons of water weekly - unless you are experiencing regular rainfall in spring and early summer. Once the taproot develops, sunflowers are able to withstand drier conditions.

Fertilizing: While sunflowers will grow just fine without any extra nourishment from the gardener, they will produce stronger, sturdier stalks and larger flowerheads when fertilized. If you choose to feed them, here's how:

Before planting, amend the soil with a 2- to 3-inch thick layer of compost. You can either add a diluted organic liquid fertilizer every few weeks when watering, or add a granular organic fertilizer once the true leaves form. Use a low-nitrogen fertilizer, such as 5-10-10, to avoid a large leafy plant with few flowers.

Trimming & Pruning: The main reason to deadhead (trim) spent sunflower blooms is to collect the seeds. Annual sunflower varieties will produce either one large head or an abundance of smaller heads. Deadheading the multiple-headed sunflower varieties cleans up the look of the plant as well. Perennial sunflowers benefit from deadheading, as it inspires them to produce a second round of flowers later in the (late) summer. Sunflowers self-sow rampantly, so expect to have many seedlings growing in spring.

You can prune annual sunflower varieties to reduce the height and encourage more flowers. Once the main flower bud forms, pinch it off. This may delay flowering, but more side buds will form and you'll get a bushier plant.

Mulching: Mulching sunflowers is not necessary; however, those dealing with dry climates may choose to do so. Wait until your sunflowers are established and apply a 2- to 4-inch layer of straw or bark mulch, leaving a ring of bare soil around the stalk so that the mulch does not make contact with the plant. This will help preserve soil moisture and prevent weed growth. Once sunflowers are older, the large leaves will shade out any weeds trying to grow between the plants.

Sunflowers: End of Season Care

Dividing & Transplanting: While you can start seedling sunflowers indoors in spring 4 weeks before the last frost date, they won't grow as fast and as strong as those direct sown in the garden. However, transplants are a good option for small-space gardeners, container gardeners and those planting dwarf sunflowers that don't have as aggressive a root system. Annual sunflower varieties aren't divided, but perennial sunflowers should be divided every 2 to 3 years to keep them vigorous. In spring, dig up the sunflower plant and divide the clump into 1 to 2 foot diameter sections with a good root system and stalks. Replant in a full-sun location on fertile, well-drained soil.

Pests and Disease: The biggest pest of sunflowers aren't usually diseases or insects, but animals. Rabbits, deer and wood chucks love to munch on young sunflower plants. To prevent damage, place 3 ft tall wire fencing with small holes around the sunflower row or clumps. For deer, plant sunflowers in a 7 ft fenced area or try using repellent sprays with active ingredients such as garlic, cayenne, rotten eggs and blood meal. Rotate the sprays periodically through the spring and early summer. For birds that love to dig up sunflower seeds and seedlings, protect the seeds and young plantings with a floating row cover.

Sunflower seedlings can also be attacked by cut worms. Cultivate around your sunflower patch with a garden hoe in spring to expose the cutworms to the weather and predators. For small plantings, place cardboard toilet paper roll 'collars' around individual seedlings to prevent damage. Alternatively, sprinkle diatomaceous earth around the planting area to discourage cut worms. They don't like this sharp substance.

Seedlings can also be attacked by slugs and snails, especially during periods of wet weather. Use diatomaceous earth or sharp sand around the seedlings to protect them, or sprinkle an organic bait containing iron phosphate to kill the slugs. They are attracted to this bait, but while the iron phosphate is toxic to slugs and snails it is safe for wildlife, pets or kids.

Additional Concerns: Sunflowers are stalky plants. When cleaning up the garden in fall, don't try to compost the whole stalk. Instead, shred or chop them up them first. They will break down much faster in the compost pile.

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