Last updated on October 22nd, 2023 at 08:58 pm
Sunflowers are one of the most joyful flowers to share, and we certainly have been growing a ton of joy at the flower farm. Having sunflowers that last until the end of the season is very important for us. If you are wondering how late can you plant sunflower seeds, then you have come to the right place.
In order to have these beautiful blooms right until the end of the season, we had to answer that exact question:
How Late Can You Plant Sunflower Seeds?
To know the latest date that you can plant sunflowers, you must first identify the growing time for the variety of sunflowers being planted. Then determine the first expected fall frost date for your growing zone. To find the latest sunflower planting date, count back the number of growing days from the date of your first fall frost.
This is what we do, and we have had sunflowers growing well into October.
We grow annual sunflowers, or Helianthus annuus. There is a perennial variety that can be grown as well, Helianthus maximiliani, but for the sake of this post, I will be referring to the annual plant.
In fact, next year we plan to push the boundaries to try to have sunflowers until the end of October.
Of course every growing season is different.
Some years the fall frost comes earlier than expected. Other years we have later frosts, as was the case just last year when we still had dahlia plants blooming in early November.
If you have unpredictable frosts in your growing zone, just be aware that your late planted sunflowers may be at risk to frost damage by an earlier than expected frost.
When Can I Plant Sunflower Seeds Outside?
Planting Sunflower Seeds Versus Sunflower Transplants
Sunflowers are tough plants with long tap roots. They are one of the easiest flowers to grow if planted in the right way and in the right spot.
Planting sunflower seeds outside directly into the garden is the absolute best way to plant these flowers.
I am a gardener and flower farmer who starts most flower seeds indoors, to get a head start before the season warms up. However I have learned from experience that direct seeding sunflowers is the best way to plant them.
I have seen the enormous difference between transplanted sunflowers grown from seeds planted indoors, and those that are directly planted into the garden. Those planted directly from seed into the garden are the strongest plants.
The sunflower seedlings started indoors and transplanted out were weaker plants with smaller flowers, and never really caught up even after planted out into the garden.
The direct planted sunflowers are the best, most sturdy and rigorous growing if they are able to establish their roots in place without disruption. Hands down.
When To Plant Sunflower Seeds Outside
So to answer the question as to when to plant sunflower seeds outside, that would also depend on your growing zone. Direct sow seeds outside after your last spring frost date in late spring. You can find your frost dates here.
For best results, plant sunflower seeds in an area that gets full sun. Plant as well in an area with fertile soil, as sunflowers are heavy feeders. Give a sprinkle of slow-release fertilizer when planting for good growth.
Sunflower seeds need warm soil to germinate, so plant when soil temperatures begin to warm. If the soil begins to warm up after they are planted they will be stimulated to grow.
It generally takes the seeds several weeks to germinate and poke their seedling heads above the soil. By that time the risk of further frost should be clear.
Sunflowers are cold sensitive, and should not be exposed to frost if possible. I have found however by using the last frost date in spring as a guideline, we have not lost sunflowers at this time of year.
How Long Do Sunflowers Bloom?
Sunflowers bloom for several weeks, when the blooms open up.
If growing for cut flowers, the best time to pick is when the bloom just starts to open, and you can see the flower petals just starting to lift.
Single stem sunflowers will bloom only once. Branching sunflowers will produce multiple stems which will open up in succession.
In order to have sunflower blooms for a longer period throughout the growing season, you can succession plant the single stem sunflower seeds on a weekly basis.
This will allow tor an extended bloom time, and continuous blooms with multiple harvests throughout the growing season.
What Month Do You Plant Sunflower Seeds?
If direct seeding your sunflower seeds into the garden, the months in which you plant sunflowers is dependent on your usda growing zone. Essentially the dates fall between the last spring frost and the first fall frost for your growing zone.
Keep in mind that the last seeds planted should have time to grow to full maturity before the first fall frost, so be aware of the timeline of days to maturity for the variety of sunflowers that you are planting.
Let’s have a closer look at this timeline.
How Long Do Sunflowers Take To Grow?
There are many different types of sunflower and sunflower varieties, with variations of growing times to maturity. If you are planting sunflowers for cut flower harvest, there are many varieties to choose from.
There are fast growing single stem pollenless Sunflower types, such as the Procut series which can mature in as little as fifty to sixty days. Then there are other similar cultivars may take seventy to eighty days to mature.
The sunflowers with faster growing times can be succession planted throughout the season. Planting a row of these seeds every week ensures the availability of fresh cut sunflowers throughout the season.
Then there are branching varieties that can take a little longer to grow. The larger branching varieties can take up to ninety five days to mature.
If you are planting sunflowers for seed, such as the large Mammoth Russian variety, growing time is much longer than for the pollenless types.
These sunflowers are planted at the beginning of the season. They will grow and mature as the season progresses, with seed harvest at the very end of the growing season. These sunflowers can take up to 120 days to mature.
Growing Time For Sunflowers Grown In Zone 5
We are in zone 5b, and mainly grow the single stem pollenless sunflowers which we succession plant weekly if possible, weather dependent.
These seeds take about two weeks or so to germinate, depending on the weather. Then it will take another two months of growing to get mature blooms.
We use a mechanical planter for ease of planting and to sow sunflower seeds. The device is called a Jang seeder, and can plant the seeds very quickly and easily into a prepared bed, in no time flat.
Our first row of sunflowers was planted mid-May. Since it was a little cooler in the spring, the seeds took a bit longer to germinate and grow. These early planted flowers were also smaller and not quite as robust as the sunflowers planted a little later in the season.
A new row of sunflowers was planted every week throughout the summer months. We continued to plant until the latest planting date determined for our growing zone, which was mid July.
The last rows of sunflower seeds were planted in mid July. From these succession plantings, we harvested sunflowers until mid October.
Is It Too Late To Plant Sunflower Seeds In June?
If you are planting sunflowers that will grow to maturity within sixty to sixty five days, you will definitely be able to plant these sunflower seeds any time in June.
Consider the time frame to maturity for your seeds.
If you plant the seeds at the beginning of June, it will be several weeks or so before they germinate. Then it can take another sixty days to bloom ( if they are the fast growing sunflowers ). You will likely have blooms in mid to late August.
If you plant these seeds in late June, you will most likely have blooms in mid September. Consider your growing zone and the risk of frost in mid September.
Depending on the type of sunflower, as well as your growing zone, planting sunflower seeds in June is a possibility.
As discussed, last year we planted sunflower seeds in weekly succession right until the middle of July. According to our first fall frost date, that was the safest date to stop planting.
Because we had such a warm and frost free fall, we ran out of sunflowers early. I realized that we could have planted right until the end of July that year.
It is always a risk if you push your planting limits however, so just be aware of this fact.
If you are planting just on the cusp of where your sunflower blooms and the first frost date coincides, you may be just fine, or you may have some loss. Sunflowers can tolerate some light frost however.
There is always a risk of early frost as well, especially in fall. It’s really hard to predict those types of factors, so far in advance.
Can You Plant Sunflower Seeds In August?
Sunflowers love the heat, and grow best in warm summer soil, and in the warmth of the warm summer sun.
In warmer growing zones such as zones 8 and above for example, it can remain warm and frost free until much later in the year.
Planting sunflowers in August in warmer growing zones, especially the fast growing varieties, is definitely an option.
Sunflowers are a choice cut flower in our garden.
We grow lots of them in a very short growing season. It is therefore very important for us to know how late we can plant our sunflower seeds.
This information is valuable for any gardener growing sunflowers. There is a time limit however on when to stop planting.
Knowing your frost free dates as well as your sunflower growing times will allow you to plan your planting times and take advantage of the entire growing season.
Many gardeners plant their sunflowers at the beginning of the season, and only once in the season.
It’s nice to know however, that some sunflowers can be planted later, and even throughout the season. Start a new row of seeds every week for a summer full of beautiful sunflowers.
It truly is amazing to see how people react to sunflowers, and the joy that a big sunflower bouquet can bring.
Knowing the joy that sunflowers can bring has prompted us to learn more about how to grow lots of them throughout our short zone 5b growing season.
Have you ever wondered how late you can plant sunflower seeds? Have you ever planted your seeds later in the season? Be sure to leave a comment to share your experience!