How To Grow Giant Zinnias (Tips For 6-ft Tall Plants)

orange zinnia with two layers of petals

Imagine having plants that are 6-feet tall and covered with colorful flowers as big as the palm of your hand. That is what giant zinnias will give you. They are the eye-catching focal point of any garden, and they’re straightforward to grow.

It all starts with the right seed packet and the proper care to grow these giant beauties.

Grow giant zinnias by starting with the right seed variety, such as Benary’s Giant or California Giant. Sow the seeds in rich soil that gets at least eight hours of sunlight daily. Water and fertilize regularly, and in three months, you will have zinnia plants five feet tall or more with enormous blooms. 

Anyone can grow huge zinnias if you know a few gardening tips, which will serve you well for more than just zinnias.

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Giant zinnias for giant blooms

Giant zinnias are a fun flower to grow. They get very tall and produce huge flowers that make a great focal point in the garden or when cut for bouquets. I love how they add a touch of whimsy to any garden. They are also relatively easy to care for and don’t require much attention.

Giant zinnias can be very tall or produce huge blooms, like this one.

If you have kids, these tall zinnias are perfect for growing alongside sunflowers so they can hide among the leaves and watch as the flower grows taller than them.

Choose the right variety

If you want the zinnia blooms on your plants to be huge, you have to plant the right varieties. There are hundreds of different zinnia cultivars and hybrids ranging in height from 6-inches to 6-feet tall plants. Blooms can be single or double and range from 1-inch across to 6-inches across.

Choose a variety with the word ‘giant’ in its name to really hedge your bets. These have been bred to grow the largest plants and produce the biggest blooms.

Also, look for the giant varieties that produce fully double blooms. Single blooms can be 6-inches across, but the double blooms will look larger because they are fuller. Choose one of these varieties if you want to grow huge zinnias.

If you’re not sure what the difference between single and double zinnia blooms is, jump over to this article to find out: 5 Types of Zinnias Flowers (Which are the best for cutting?)

Benary’s Giant

Benary’s Giant will reach a mature height of 5-6 feet and produce fully double blooms 5-6 inches across. This zinnia has strong stems and makes excellent cut flowers with a long vase life.

It’s a vigorous plant that holds up well in the summer heat and remains upright during heavy summer rainfall. Benary’s Giant has a low susceptibility to powdery mildew, making them an excellent option for humid climates.

Benary’s Giants is the variety you’ll find grown by most flower farmers who depend on big harvests of long stems and vibrant blooms to catch customers’ eyes.

California Giant

California Giant will reach 5-6 feet tall when mature and produce huge 5-inch blooms all summer. This variety looks very similar to Benary’s Giants, so it’s a good alternative if you can’t find seeds for the first variety.

As with all zinnias, this is a cut and come again variety that makes excellent cut flowers.

State Fair

State Fair Giant zinnias grow to be 4-feet tall and produce huge 5-6 inch blooms. The State Fair Giant has blooms in multiple colors, and some of the bloom colors are not available in any other variety.

This giant zinnia has been bred to be strong, vigorous growing plants perfect for a tall garden challenge.

Plant in full sun and rich soil

Zinnias of any type thrive in an area with full sun, but a sunny location is vital if you’re trying to grow your flowers as tall as possible. Strong sun will help the zinnia have the energy needed to grow stems strong enough to support the vertical growth.

Rich soil will also help support the zinnia’s upward growth. Add compost or manure to the planting area a few weeks before you plan on sowing the seeds. The compost will help increase the nutrient levels and organic matter in the soil.

Water and fertilize regularly

Like all plants, zinnias need a consistent water supply to grow their best. These tall plants have an extensive root system and need deep, periodic waterings. You definitely don’t want to water shallowly every day. That will encourage shallow root development, struggling to anchor the plant as it becomes top-heavy.

Once or twice a week, saturate the ground with water deeply. If the weather is hot, you might need to water once more during the week, but resist the urge to water every day unless your plants are consistently exposed to extreme heat.

Regular applications of fertilizer or compost will keep the giant zinnias fed, but don’t go overboard. Too much fertilizer can cause the zinnia to grow faster than it should, leading to a weak stem that is bound to flop over.

That’s not ideal when you’re trying to grow giant plants!

The zinnias grow so tall and wide that the plants shade out weeds, so they don’t need to be mulched. However, adding a 2-inch layer of compost around the base of the plants will increase the soil’s nutrition and amount of organic matter.

Higher amounts of organic matter improve the ability of soil to drain, which is great for zinnias who resent soggy feet. Standing moisture will lead to root rot and mildew diseases, so drainage is a must.

Stake to keep them upright

These tall-growing giant zinnias will need to be supported to keep them upright all summer. While they have strong stems, the plants become heavy with blooms, and a summer thunderstorm with high winds and heavy rains can topple over the tall plants.

There are several methods of keeping them upright – like planting them near a porch post or using tall stakes. Choose a process that is easiest for you to execute to keep the plants standing upright.

For several done-for-you ideas, check out this article: 8 Ways To Stop Your Zinnias From Falling Over.

Deadhead and harvest frequently to promote blooms

There’s no point in growing giant zinnias if you only get a handful of flowers off the plant! Take an extra moment to deadhead your plants to keep them pumping out giant pom-pom shaped flowers.

pink zinnias with one faded bloom
Deadhead spent blooms like this one.

Deadheading is simply removing the old dead flowers from the plant. It keeps the plant looking neat and promotes more growth. Use a pair of sharp scissors to snip off the dead flowers near the stem.

Zinnias are called ‘cut and come again‘ flowers because the more you cut the blooms off, the more blooms the plant will produce. Harvest the flowers frequently to promote growth, and deadhead any left behind that start to fade to keep the plant in high production.

Need to learn about deadheading? Learn here: Should You Deadhead Cut Flowers, Too?


How long does it take giant zinnias to bloom?

Even though giant zinnias mature to be much taller than other zinnia varieties, they don’t take much longer to bloom. You can expect blooms about 90 days after planting as long as the seeds are sown in warm weather.

How big do giant zinnias get?

The biggest zinnia varieties will reach at least six feet tall, and other giant varieties will reach only 4-5 feet tall but have enormous blooms, adding to the “giant” nature of the plant. The better the soil and the more sunlight a zinnia plant gets, the more lifely it is to reach giant status.

Are giant zinnias perennials?

Giant zinnias are annuals and will not return the following year unless some flowers go to seed and self-sow. To encourage self-sowing, leave some flowers on the plant to drop seeds at the end of the season. They’ll sprout next spring when the temperature is right. 

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