When to plant sunflowers: Planting sunflowers, Helianthus, that are perennials, can be done anytime during spring, when all danger of frost is gone.
Perennial sunflower clumps can expand quite a bit, so I recommend that you space them about 3 feet (90cm) apart when planting them to avoid overcrowding.
The planting hole should be about 2 feet wide and 1 foot deep. The reason the hole should be wide is to allow the feeder roots to grow fast. They grow wider than deep.
Plants need to grow below ground first before they are able to grow above the ground.
So the loose soil in a wide dug hole will help your sunflower plants grow so much faster.
I also recommend that you add a cup of bonemeal to the planting hole and mix it with the amended soil.
All sunflowers should be planted in full sun for the best flowering.
They tolerate heavy clay and a wide range of pH soil conditions.
Pinch, or trim back, the plant several times from mid-spring to early summer if you want to control the height.
Newly planted sunflowers should be watered regularly if there is not enough rainfall to water them enough.
Apply a light layer of organic mulch before summer to keep the soil moist during hot weather.
If you are planting sunflowers in the fall, either from divisions or from purchased plants, it should be done early in the fall, so the roots have time to grow before the cold weather comes.
During summer stake taller varieties and fertilize sparingly to avoid sprawling.
Taller plants should be planted at the back of the border for the best flowerbed display.
Planting Sunflower Helianthus Annus From Seeds
The annual sunflower, Helianthus annus, or Common Sunflower, are usually sown from seeds in spring where the plants are supposed to grow.
These are the sunflowers that have flowerheads the size of dinner plates.
It’s quite simple, even a kid can do it. In fact if you have kids, plant some sunflower seeds with them every summer.
It was a tradition when I was a kid growing up in Sweden, and I have such fun memories from watching the sunflowers grow so tall.
Just follow the direction on the seed packets, and you will have beautiful sunflowers by summer.
The large flowered annual sunflowers need rich, moist soil, in direct contrast to the perennial sunflowers.
So be sure to amend the soil with composted manure, before planting the sunflower seeds.
You can roast the sunflower seeds and eat them, and the birds enjoy the raw ones in the fall and winter