Sunflowers are a cheerful sight in the garden, so it’s no wonder gardeners want to know just how late they can be planted. With a timely midsummer sowing of sunflowers, you can get blooms up to your first frost. Keep your vases full of cut stems, or enjoy those sunnies right in the garden.
Sunflowers can still be planted in July and August in USDA zones 7 and higher. Zone 6 or lower will need to plant out by June or July to get blooms before the first fall frost. In any zone, choose a single-stem sunflower with the fewest days to maturity to get flowers as soon as possible.
Here are a few tips to help make that happen, starting with knowing how your garden zone affects your planting time.
Or, for a deeper dive into starting a late garden, click on this episode to find out how I’m starting a garden from scratch this summer and how you can, too:
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What is the last month to plant sunflowers?
The last month to plant sunflowers will depend on which USDA garden zone you are in and your first expected fall frost, as well as the sunflower’s days to maturity. To find both your zone and frost date, you can look them up by zip code. Use those dates plus the days to maturity to determine the last planting for your sunflowers.
I’ll break down some general planting dates by zone and the last possible planting date to still get sunflower blooms. Please note that these dates are approximate and show the range of the A/B division in zones.
For example, zones 7a and 7b can vary by 5-10 degrees Fahrenheit in the winter. This means that zone 7a will experience a frost sooner than 7b. So to get a more accurate date for your specific area, be sure to use the tools linked above.
Lastly, the chart below refers to using sunflower variety ProCut Orange, a classic golden sunflower that needs 50-60 days to mature. It’s a quick-growing variety that’s great for midsummer plantings. The planting date is then found by counting backward from the first fall frost, plus two weeks to allow for slower fall growth and a bloom time window.
For example, in zone 6 with a first expected frost on October 10th, I will count back 60 days plus 14 days, so 74 days, for a planting date of July 29th.
|First frost date
|June 27-July 3
|Sept 25-Oct 8
|July 29-Aug 12
|Oct 30-Nov 10
|Nov 7-Nov 20
|Aug 26-Sept 8
|Dec 30, infrequent
Zone 10 and above may not freeze at all, but the days will be short and the nights cold, so don’t be surprised if the plant growth is relatively slow and the blooms smaller.
How long do sunflowers take to grow?
Single-stem sunflowers take between 50-75 days from planting to bloom, so choose a variety based on how much growing season you have. If you are only 60 days away from your first expected frost, choose the quickest-maturing variety you can find.
Single-stem sunflowers are fast-growing because the plant only produces one stem and one flower. Branching sunflowers produce a central stem with many branches and blooms, so they take longer to mature. For this reason, it’s best to focus on single-stem varieties when there isn’t a lot of time left in the growing season.
For more specifics on how much time you need to get fully mature sunflowers, this article will have all the details: How Long Do Sunflowers Take to Grow? (Know What To Expect When).
As summer progresses, the days will get shorter and cooler at night. This can add time to the days to maturity for any plant, including sunflowers. Especially in the lower zones, add a week or two to the maturity time to (almost) guarantee enough weeks for your plants to bloom.
If you want to dive deeper into which of the single-stem sunflower varieties you should grow, check out this post What Sunflower Varieties Are Best For Cutting?
How to plant sunflowers for quick growth before a fall frost
There are a few other tricks you can use to help get your sunflowers blooming quickly so you can still enjoy them before your first fall frost.
Sunlight and Soil
Sunflowers grow best in full sun, so choose a site that will get as much sun as possible even as summer wanes. Sunlight access will be critical when the plants are small. You don’t want your two-week-old sunflowers seedlings getting shaded out by the four-foot-tall cosmos plants in the next bed.
A late planting of sunflowers will probably do best planted at the edge of your garden to minimize any competition for sunlight, which will reduce your chances of getting blooms by the end of the summer.
In addition to good sunlight, provide rich soil to support fast growth for your sunflowers. These flowers are heavy feeders at any point in the season, but when you’re racing the clock with a late planting, it’s vital not to skimp on the soil.
If you can, add a few buckets’ worth of quality compost to the planting bed, so there is a fresh source of nutrition for the sunflowers.
Alternatively, you can add an all-purpose fertilizer to the seedbed when you sow seeds, with a second application a month later. Be sure to read the instructions on your fertilizer package to know exactly how much and when to apply it.
Once you have your bed set up, direct sow the sunflower seeds by dropping them about an inch deep in the soil. Since these are single-stem varieties, they don’t need much space, so place your seeds about six inches apart. This spacing helps keep the stems smaller for cutting so they fit in vases and arrange well with other flowers.
If you have a lot of crows or squirrels in your area, you can cover the seedbed with a piece of burlap or an old bedsheet to keep the critters out until the seeds have sprouted. You can even water right over the top, and the water will run through down to the soil.
Just be sure to remove the cover once the first seeds start to pop up so they can get full sunlight right from the start.
After that, it’s just a matter of time before your sunflowers grow tall and develop flower heads to give you the last show of the summer.
If sunflowers aren’t the only flowers you want to squeeze in before your first fall frost, get some other ideas from this post, Too Late To Plant A Flower Garden? A Guide To Summer Planting and get some cosmos, zinnias, and other flowers in the ground!