How To Plant Sunflower Seeds For Stunning, Sunny Blooms That Last All Summer

For many gardeners, learning how to plant sunflower seeds serves as a rite of passage. Cheerful yellow blooms that are easy to grow from seed make the ideal plant for gardeners of all ages and skill levels. Sunflowers’ adaptability and resistance to disease further lend to their charm and popularity.

Still, knowing how and when to plant sunflowers seeds is key to growing this classic garden flower. In this guide, we’ll explore how to grow sunflowers from seed in greater detail and cover the growing journey from planting to transplanting in the garden.

Where to Plant Sunflowers

Those interested in growing sunflowers from seed should consider the mature plant’s needs carefully. Sunflowers perform best where they receive full sun throughout the majority of the day, at least 6 to 8 hours. Optimal conditions include good drainage and soil that is nutrient rich and well-amended.

Where conditions are less than ideal or space is tight, home gardeners can grow sunflowers in containers. For the best results, use a high-quality potting medium and plant sunflower seeds that are a container-friendly cultivar.

When to Plant Sunflower Seeds

Like knowing when to start seeds for your vegetable garden, knowing when to plant sunflower seeds is important to the success of your flowers. Most seed packages suggest sowing directly into the ground after all danger of frost is past. That's fine if you live in an area where your growing season is long enough. However, if you live somewhere where the growing season is short, you may not have enough time to direct sow seeds in the garden.

Sunflowers can take anywhere from 70 to 120 days to mature with the larger varieties taking the longest. Most gardeners like to get a jump on the season by starting seeds indoors about three weeks before the last frost date so they can enjoy blooms earlier.

Though there are both annual and perennial sunflowers, most varieties are tender annuals, which means they are unable to withstand cold and freezing temperatures can kill them.

For annual varieties, you must wait until all chance of frost has passed in the spring before you plant sunflower seeds outdoors. Soil temperatures above 50 F (10 C) are necessary for germination. To extend bloom time, continue sowing sunflowers throughout summer, a tactic known as succession planting.

How to Plant Sunflower Seeds

You can plant sunflower seeds a few different ways. Most commonly, gardeners sow sunflower seeds into the garden after the weather warms up in spring. However, another option is to grow sunflower seeds indoors first and then transplant them outside once outdoor temperatures rise.

Sow seeds into trays, like Vego Garden’s Jumbo Seedling trays from the Gardening Know How Shop, no more than two to three weeks before the last average frost date. For those planting larger cultivars like the ‘Giganteus’ sunflower, it’s best to start seeds indoors early to give them plenty of time to grow.

Starting Sunflower Seeds Indoors

When starting sunflower seeds indoors to transplant later, first fill your container or tray of choice with a quality seed starting mix, then plant your seeds, and cover them with about 1 inch (2.5 cm) of soil. Water well and keep soil moist. In a week or two, your seedlings will push through and start to grow rapidly.

Direct Sowing Sunflowers

If you’re direct sowing sunflowers outside, first you need to choose a sheltered place out of the wind or a spot along a fence where you can tie the stalks as plants grow tall. Sunflower roots grow deep and wide, so turn the soil well before planting. Add plenty of compost because large flowers need good nutrition.

How deep to plant seeds isn't as important as how far apart you plant them. After all, seeds dropped from previous year's flowers often sprout where they fall. If you look at the back of your seed packet, most recommend planting sunflower seeds about 1 inch (2.5 cm) apart. Though this can vary depending on the variety.

You can also overplant, or start by planting seeds closer together, and then thin out the weaker seedlings later. Overplanting can also help combat greedy wildlife that might eat your sunflower seedlings.

How to Transplant Sunflower Seedlings

Before transplanting sunflowers outdoors, seedlings require a brief hardening-off period. To harden off sunflower seedlings slowly expose plants to outdoor conditions over the course of several days or weeks. This helps prevent stress and loss of plants as seedlings become acclimated to their new home.

When transplanting sunflower seedlings, handle with care and make sure not to disturb their roots. How you space plants depends on the size of your sunflowers at maturity.

For the giants, you'll need 2.5 to 3 feet (0.75-1 m) between each plant for optimum growth. For regular sized sunflowers, you will need 1.5 to 2 feet (0.25-0.5 m). For shorter varieties, you only need about 6 to 12 inches (15-31 cm). Once situated into beds, water new plants deeply and keep beds free of weeds.

Sunflowers are a favorite treat for wildlife. Birds and squirrels love to eat sunflowers and can easily destroy your crop. They can dig up seedlings as fast as you can plant them. If you find yourself at war with these backyard thieves, cover sunflower seedlings with a piece of fencing or a wire cloche.

Frequently Asked Questions

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