Too Late To Plant A Flower Garden? A Guide To Summer Planting

summer tolerant annuals of zinnia and cosmo in garden

It’s happened to all of us gardeners. You meant to get the garden in early. By the latest, you swore you’d have your seeds and transplants in the ground by May. But life got in the way, or a wet spring pushed back all your plantings. Or maybe you did get some spring flowers going, but by summer, you’re wondering if there’s time to squeeze in just a little more.

Whatever the reason, it’s not too late to plant flowers in summer and still get fresh cut flowers from your garden. There are even some benefits to planting a mid-summer garden that you can take advantage of.

You can plant annual flowers as late as July or August if your average first frost date is at least 90 days away. Several types of annuals, such as cosmos, marigolds, calendulas, and zinnias, will bloom in 60-75 days, so 90 days gives those flowers at least several weeks to produce blooms.

So even if you’re at the halfway point of your summer, you can still grow plenty of flowers for the remainder of the season. I’ve even got some recommendations for you in this article.

I also recorded a podcast episode all about summer planting if you’d like to listen on the go! This episode isn’t specific to flowers but has many little tips for starting a garden later in the season.

Ready to plan and grow a thriving garden packed with flowers and veggies?

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How late can you plant a flower garden?

You can plant a flower garden as late as August as long as you have enough weeks in summer left for the plants to mature and bloom. Annual flowers such as cosmos, nasturtiums, and zinnias will all reach maturity between 60-90 days, so choose a variety based on how much growing season is left.

Here’s an idea of some fast-growing flower varieties for summer planting:

FlowerVarietiesDays to maturity
CosmoDouble Click,
SunflowerZohar, Buttercream
Gold Rush
Teddy Bear
MarigoldRed Gem60
CalendulaFlashback Mix,
Pink Surprise
Pacific Beauty

ZinniaQueen Series,
Sunbow Mix
Oklahoma Series,
Benary’s Giants

StrawflowerMonstrosum Mix
Copper Red
BasilMrs. Burns’ Lemon
Dill (leaves only)Bouquet40-45
Runner BeansScarlett Emperor45-55

If sunflowers are your favorite summer flower, read How Late Can You Plant Sunflowers? Check Your Zone And Date Here to get the specifics.

Two important considerations for summer flower plantings

So you can see it’s not too late to plant a flower garden, but there are a couple of distinct considerations that will influence what you can grow and when.

It’s easy to plan which varieties to sow when you have this information. Let’s take a look.

1. First average frost date

The first average frost date is the estimated date the temperature in your growing zone will drop low enough to create a frost outside overnight, around 32-29 degrees. Some frost-tolerant annuals can survive these temperatures. A 28-25 degrees hard freeze will kill even those hardy annuals.

garden flower is drooping after frost

If you know you’ll have a hard freeze, select varieties of flowers that will bloom before these colder temperatures arrive for the winter.

If you aren’t sure what your average first frost date is, you can quickly look it up using your zip code. Use this guide at Farmer’s Almanac and record the date for your area.

While researching, don’t miss this post, Will A Frost Knock Out Your Zinnia Flowers?

Days to Maturity

Days to maturity refers to the time a plant needs to go from planting to bloom. The date range refers to when the seed is sown, not when the transplant is put out in the garden. Most annual cut flowers bloom in a range of 60-110 days.

To get blooms from a mid-summer planting, choose varieties with the shortest amount of days to maturity and save the slower growers for next summer.

The flowers suggested here are all in the 50-90 days range, hopefully giving you enough blooms to fill your vases for at least a few weeks before the summer is truly over.

Use your first frost date & days to maturity to select plants

Once you have your first average frost date and days to maturity, all it takes is a little backward counting to figure out which flowers will work for you and your area. Here’s an example:

First frost dateDays to maturityPlanting date for
4 weeks of blooms
October 15th60 daysJuly 19th

This math allows for a month of bloom time. According to days to maturity, the actual planting date would be August 16th, but that wouldn’t leave any time for the flower to bloom, so I counted back an extra four weeks.

If you want to aim for six weeks of blooms, start those seeds a couple of weeks sooner. Even if your first frost comes a little earlier than expected, you should still be able to get two to three weeks’ worth of flowers from the garden.

Coddle your seeds so they can withstand the summer heat

The most important thing you need to plan for with summer sowings is to water, water, water. If the seeds are moist enough to sprout but then are allowed to dry out, your newly germinated flower seeds will die. There go your last hurrah of cut flowers.

So be very diligent about keeping the seedbed moist. That might mean hand water twice a day until the seeds have sprouted, and your drip irrigation can take over. Another method would be to put an overhead sprinkler on the seed. Use whichever way works for you to keep your seeds from drying out.

sprinkler watering flower garden

You can hedge your bets against dried-out soil by starting your seeds in trays or soil blocks and transplanting them when they have two sets of true leaves. That will usually take a few weeks at this point in the year.

If you go that route, make sure to harden off your seedlings by slowly exposing them to the warmer outside temperatures for a few hours per day. Set your transplants in dappled sunlight to also get used to the sunlight. Bring them back in at night and set them out again the next day for a bit longer.

Hardening off usually takes a week of bringing the seed trays in and out each day, but it’s worth it to avoid losing your baby seedlings to transplant shock and harsh weather.

Enjoy quick growth and fresh blooms with summer flower plantings

It’s not all bad when you plant a bit later in the season. You’ll get to enjoy a couple of benefits that will yield more flowers than if you only sowed in the spring.

Summer heat encourages quick growth

When you plant flowers in spring, certain varieties may get off to a slow start if the weather stays on the cooler side. This is especially true for warm-season annuals such as zinnias and cosmos. Even if you planted them earlier in the year, they wouldn’t sprout or thrive because the soil is too cold.

So by making a mid or late-summer planting, you’re avoiding the hassle of cooler soil temperatures and slower plant growth. When cosmo, zinnia, or other warm-season annuals are planted into warm soil, they’ll germinate much more quickly and launch straight into fast growth.

Your plants will need regular watering to survive the summer heat, so either set up some drip irrigation or water regularly.

Enjoy a second flush of flowers

Additionally, spring-planted annual flowers can sometimes start to fade once the heat of summer comes in. This is especially true if the flowers are planted early in the year and harvested regularly. The plants will start to look a little scraggly and, unless well-fertilized, may begin to slow down in production.

Even if the plants are still going strong come July, the heat might start to fade out the color on vibrant blooms such as a Benary’s Giant zinnia.

You can get around this with your summer planting. Since the plants will be doing most of their growing, not blooming, during the summer heat, they’ll give you a new flush of flowers once the peak of summer heat has passed.

You’ll also be sure to get sturdy blooms that will keep their vibrant color and hold up well in the vase instead of potentially being a bit dried out or faded.

So even if you were worried that it was too late to plant flowers, rest assured that you’re still on track to get flowers before your growing season is over. It may even turn out that you get more vigorous blooms than you expected.

Plus, you can plan for colors that will ease your season, from the pinks and whites of summer to the reds and oranges of fall. For some ideas, jump over to this post, Plant Zinnias In Summer For Easy Blooms And Fall Color.

Remember that Mother Nature’s timing is fickle

The final thing to note is that the coming fall weather can impact how well and quickly your summer plantings grow. The shorter days and cooler nights can add a week or more to the time until the first bloom, so if you are very time-crunched before a light frost hits, choose the quickest-maturing varieties.

Mother Nature is a fickle beast, so you might get lucky and get a mild fall that keeps your flowers blooming until the end of October.

Or she might bring a cold snap that kills everything in September. You have to take the gamble and see what happens.

If you’re worried about an early frost taking out your flower garden, check out this post, Will A Fall Frost Kill My Cut Flowers? and plan ahead to keep the garden pumping out flowers.

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