Sow perennial sunflower seeds either in the fall or in the spring after the last frost. (Get seeds here.) If sowing in the spring, the seeds must first be cold stratified, which means they need a period of cold to germinate. To cold stratify the seeds indoors, start about 8-10 weeks before your spring frost date.
Plant sunflowers in late spring, once the ground is nice and warm. Most sunflowers germinate when soil has reached 70 to 85 degrees F. The best time to plant sunflowers is just before the soil reaches this temperature. Look for a ground temp of between 60 to 70 degrees.
The soil was too wet or too dry:
Too dry, and your seeds won't germinate. Too wet, and they're liable to rot. Ensure that seeds are kept evenly moist by thoroughly wetting and draining the compost before you begin.
Soak Sunflower seeds with warm water (40-50 C) for 25 minutes with the aim of breaking the seed dormancy period (awakening the seed while accelerating germination).
Sunflowers that have reached the R7 stage can withstand temperatures down to 25 °F (-4 °C) with only minor damage. Only a frost duration of 6 hours or more below 25 °F would penetrate the thick layer on the back of the sunflower head and cause damage.
Sunflowers and Light Requirements
Sunflower seeds do not require light for germination. However, when grown indoors in pots, the plastic wrap is removed at the first sign of germination and the uncovered pots are placed in bright, indirect light.
Overnight is usually good. Many sources recommend 8-12 hours and no more than 24 hours. Again, too much soaking and the seeds will start to decompose. If you use very hot water, the soaking time will decrease.
Sunflower seedlings should be watered daily so the soil is moist but not soaked. As the sunflowers become established, they can be watered once a week.
If hard frosts do occur, then many times only the seed in the center of the head (the last to pollinate) will be affected. Temperatures below 25 F would for all practical purposes be a killing frost.
Keep the paper towels in a plastic bag.
Put the damp paper towels in a plastic bag. Check on them once or twice a day, and continue once the seeds have sprouted. Typically, you'll see sprouts emerge from most of the seeds within 48 hours. Once this happens, move on to planting the seeds.
The narrow end of the seed is where roots will emerge, so putting this end down saves the plant from having to right itself in the ground. Place the sunflowers 1 to 2 inches deep, point-down, every 6 inches or so, and then cover them up.
Stratification is the process of giving your seeds a period of 'cold' to prepare them for better germination. If you dont stratify seeds, they can still germinate but the rate is often much lower and they can actually take 2 or 3 times longer to germinate.
Place one seed in the divot and cover it with soil. If you have extra seeds, you can put 2-3 in one hole and then trim off the two weaker seedlings. Water the soil gently to help settle it. Sunflower seeds of most varieties should be planted about 18-24 inches apart, as they will grow to be quite large.
While you can germinate certain seeds without soaking, your chances of success and the speed of germination can be greatly increased if you do. It can mean the difference between one or two seeds germinating or almost the whole batch when done correctly.
One method to check for seed viability is the water test. Take the seeds and place them in a container of water. Let the seeds sit for 15 minutes. If the seeds sink, they are still viable; if they float, discard, because they probably will not sprout.
Drying Seeds For Re-Planting
Rinse sunflower seeds before laying out to dry. Allow them to dry for several hours (or overnight). If you're saving the seeds to re-plant, store them in an airtight container in a cool, dry place until you are ready to plant. Label the container with the variety and the date you harvested.
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
Sprouting sunflower seeds: Significantly increases their antioxidant content. This means better health benefits for us! (Antioxidants help to decrease inflammation and damage to our cells, which otherwise can lead to the development of chronic diseases over time.)
Seeds don't need light in order to sprout. Steady warm temperature is more important for sprouting, such as that provided via a seedling heat mat. So, you technically don't need to turn your grow lights on until after they emerge from the soil.
Sunflowers are heavy feeders and deplete the soil more than many other crops – especially if you are growing them to reach a massive height so the nutrient supply must be replenished each season. Work in a slow release granular fertilizer – one that also contains trace minerals – about 8 in. deep into your soil.
There are pint-sized sunflowers that grow just a foot tall and giant varieties that reach for the sky, but you don't need a big garden to grow sunflowers. These classic summer bloomers can be planted in plastic pots, fabric planters, or even buckets.
Sunflowers are sun worshipers that grow best in spots that get six to eight hours of direct sun per day. They have long tap roots that need to go several feet into the ground, so sunflower plants prefer loose, well-drained, somewhat alkaline soil with a pH of 6.0 to 7.5.