How to Plant a Sunflower

When and where to plant

Sunflowers want full sun, six or more hours of direct light a day. They are heliotropic when young, meaning the heads track the sun, so any orientation works. Less than six hours of sun produces weaker stems and smaller blooms.

Plant after the last spring frost, once soil temperature reaches 50°F. Cold soil rots seeds rather than germinating them. In most US zones this is late April through early June. Successive plantings every two to three weeks extend the bloom window into early fall.

Soil drainage matters more than soil richness. Sunflowers tolerate average soils and thrive in conditions that would stress other annuals. Avoid soggy ground where seeds rot.

Space seeds 12 to 24 inches apart depending on the size at maturity, wider for tall multi-headed types and closer for compact branching ones. Tall types can reach 8 to 10 feet and need space behind shorter plants.

Direct sowing your sunflower seeds

Sunflowers do not transplant well. The plant grows a deep taproot in the first two weeks that breaks easily when disturbed, which is why nursery transplants rarely thrive and home-started seedlings struggle after moving. Pick fresh seeds with intact shells, since old or cracked seeds germinate poorly.

1. 1
   Pick the permanent spot The sunflower will grow where you sow the seed. Choose a spot with full sun and room for the plant at full size, since you cannot move it later without killing the taproot. Tall types can reach 8 to 10 feet and need space behind shorter plants.
2. 2
   Plant the seeds one inch deep Push each seed one inch into loose soil with your finger, then close the hole. Plant two or three seeds per spot in case some fail to germinate. Cover lightly with soil and press to settle.
3. 3
   Water and protect from birds Water the planted area to settle the soil around the seeds. Keep the surface lightly moist for the first week, until germination. Cover with light row cover or netting if birds or squirrels are around, since fresh sunflower seeds are a favorite target before sprouting.
4. 4
   Thin to one strong seedling per spot Once the seedlings are about four inches tall, snip the weaker ones at the base, leaving the strongest plant in each spot. Pulling weakens the remaining plant by disturbing its young taproot. Crowded plants compete for water and produce smaller heads.

The first month

A planted sunflower seed germinates in seven to ten days under warm soil conditions. The first leaves are two small oval cotyledons that emerge before the true leaves. The plant grows fast from there. By week three, the seedling stands four to six inches tall with two sets of true leaves.

Water consistently for the first month while the taproot is establishing. About one inch of water per week is right for most soils, more during hot dry stretches. Avoid overhead watering once the seedling is up, since wet leaves invite fungal issues.

Healthy plants reach 12 to 18 inches by week four with broad leaves and a thickening stem. The bud forms at the top in weeks six to ten depending on the type. Flowering follows 70 to 100 days after planting in most climates.

What can go wrong

1. Seeds not germinating

   Either the soil was too cold, the seeds were too old, or the surface dried out between waterings. Sunflower seeds need soil at 50°F or warmer to sprout reliably. Dig down gently and check. A firm, intact seed needs more time or warmth. A soft or rotted seed needs replacing with fresh stock.

2. Birds digging up the seeds

   Sunflower seeds are a favorite food for birds, squirrels, and chipmunks. They dig along the planting row before sprouts emerge. Cover the area with light netting or row cover pinned to the soil until the seedlings have four leaves. Remove the cover once the plant is too tall and rooted for animals to bother.

3. Stem cut through at the soil line

   Cutworms. The larvae of certain night-flying moths chew young stems at the surface and the seedling topples in the morning. Slip a cardboard collar or aluminum foil sleeve around the stem of each seedling, one inch above and one inch below the soil. Cutworms cannot grip the smooth surface and move on.

4. Slugs eating new leaves

   Holes chewed in the first true leaves overnight, with shiny trails near the damage. Slugs are most active in damp cool weather. Set out beer traps near the plants, scatter iron phosphate pellets, or hand-pick after dark with a flashlight. Avoid watering in the evening, since damp surfaces invite more slugs.

5. Leggy or floppy seedlings

   The seedlings grew tall and thin with weak stems. Almost always from too little light or too crowded a planting. Thin to one strong plant per spot and move any shading objects. The remaining plant strengthens its stem with sun and air movement over the next two weeks.

6. Multiple seedlings competing in one spot

   You planted two or three seeds per spot for insurance and they all germinated. Snip the weaker ones at the soil line with scissors, leaving the strongest. Pulling them up disturbs the remaining plant's young taproot. Crowded sunflowers produce smaller heads and weaker stems at maturity.