How to Grow Zinnias for Bright Blooms That Last All Summer Until the First Frost

A prolific bloomer, zinnias are long-favored by both pollinators and gardeners for their brilliant color and lasting appeal. If you’re growing zinnias for the first time, you are certain to find delight in their ease of growth and ability to persist throughout the entire summer season.

Zinnia flowers (Zinnia elegans) are a colorful and long-lasting addition to the flower garden. Once you learn how to plant zinnias for your area, you'll be able to add this popular annual to sunny areas that benefit from their perky blooms.

This guide aims to explore the needs of this classic annual flower in greater detail to help you keep plants looking their absolute best and blooming all summer.

Quick Zinnia Facts

Planting

If you're looking to add some bright color, grow some zinnia flowers in your summer garden this year. Here's what they need to thrive and how to start plants from seed.

Soil Requirements

When provided with good drainage and fertility, zinnias are adapted to a wide range of soil types. This includes those that are neutral, slightly acidic, or even slightly alkaline. Plants do well to tolerate varying soil compositions, including those that are sandy or consist of heavy clay.

Light Requirements

Zinnias grow best in beds that receive at least 6-8 hours of sun each day, often preferring much more. Ample light will aid in the production of strong stems, and large numbers of flowers.

Some shade, throughout the hottest parts of the afternoon, can be beneficial to plants where summer temperatures often climb. It should be noted, however, that excess shade may result in poor flower production and stems that are weak or leggy.

Temperature & Humidity

Most zinnias found in the garden are considered tender annuals. This means that they grow best where conditions are warm and are unable to withstand cooler temperatures. Ideal temperatures for growth range between 70-85°F (21-29°C) during the day and no less than 60°F (15°C) throughout the night.

Though zinnias are heatwave-proof and able to tolerate brief periods of high humidity, prolonged moisture or poor circulation can lead to the development of disease.

Planting Step-by-Step

Though planting zinnia seeds is relatively simple, knowing when and how will be essential to success. You generally have two options: growing zinnia from seed indoors or planting zinnia seeds outside.

If you want to sow zinnia seeds inside, you should do so approximately 2-3 weeks before the last frost date in your local area. This will allow ample time for germination, but prevent seedlings from growing too large before they are ready to be moved into the garden. Keep trays in a warm, sunny window or under lights until the seeds begin to sprout.

Seeds can also be sown directly into prepared beds. This is best done after the soil has warmed and all chances of frost have passed. New plantings should be watered well and kept consistently moist until germination can occur, in approximately 5-7 days.

Zinnia Care

Once you plant your zinnias, it's time to learn how to care for them so they thrive and produce blooms that last all summer long. Here's what you need to know about caring for zinnias in the garden.

Watering

After planting, zinnia beds should be kept consistently moist. Established plants will prove themselves much more water-wise, withstanding brief periods of drought with relative ease. Though rainfall is usually more than sufficient in meeting the needs of zinnia plants, weekly irrigation may be required where conditions are especially hot or dry.

Water zinnias at the base of the plant. A soaker hose, like this affordable option from Walmart, is ideal for keeping foliage and petals dry while providing much needed irrigation. The best time to water plants is early morning, which allows the foliage and flowers ample time to dry off before nightfall.

Fertilizing

The addition of a well-balanced feed, compost, and other amendments into the soil at planting is usually more than enough to see zinnias through a successful season.

Beyond planting, zinnia beds will only seldom require the use of fertilizers, with the exception of those with particularly poor fertility. If you want to encourage extra blooming, you can continue to feed plants on a monthly basis with the use of a fast-acting and bloom-boosting fertilizer, like this organic plant food from Espoma.

Pruning

Plants are beloved among those growing zinnias for cut flowers for their “cut-and-come-again” habit. Simply put, the more flowers that are cut from plants, the more each will produce. This makes deadheading, or the removal of spent blooms, an especially important aspect of zinnia care.

In addition to prolonging the production of the flowers, clipping faded buds will help to keep beds tidy and prevent the plant from going to seed. Though zinnias do not require traditional pruning, many gardeners choose to pinch plants early, which promotes branching and bushy growth.

Varieties

There are a huge array of different zinnia varieties available as both seeds and plants. You can explore dozens of different zinnia seeds and plants for sale from Burpee. But here are a few common types to try growing in your garden.

• ‘Benary’s Giant Series’ Celebrated as a cut flower, the Benary’s Giant Series produces large, showy blooms in a wide range of colors. Held atop strong stems, the cultivar is ideal for use in bouquets and boasts an impressive vase life. Available colors include pink, coral, red, lime, and many more.
• ‘Oklahoma Series’ Producing small, button-like blooms, the Oklahoma Series zinnia is ideal for cutting and pollinator gardens alike. Fully-double flowers are highly ornamental and attract hummingbirds with ease. Plants are available in a wide range of color, with salmon among the most popular.
• ‘Queeny Series’ The Queeny Series is known for its incredible double form and unique palette. Truly unlike any other, gardeners can expect plants to produce flowers in vibrant shades of lime, orange, pastel, and rosy pink.

Propagation

Those hoping to propagate the plant most commonly do so by growing zinnia from seed. This is most beneficial when increasing numbers of heirloom or open-pollinated types. A variety of cultivars can be found at garden centers in spring, though you may prefer to save your own zinnia seeds to grow your collection for free.

Though much less common, you can also propagate zinnias by cuttings. Small stem segments are removed from plants in spring, prepared, and placed into a damp rooting medium. With consistent warmth, humidity, and moisture, growers can expect rooting to occur in approximately 2-4 weeks.

Common Problems

Though most would consider the plant easy to grow, they are affected by several common garden diseases. Most prevalent among these are powdery mildew, leaf spot, and various other fungal infections. These are most likely to develop as the result of weather, poor air circulation, or haphazard watering.

To help prevent common zinnia problems, you should allow ample space between plants and water each carefully to avoid wetting or splashing foliage. Though zinnias are only rarely affected by pests, aphids and Japanese beetles can be causes for concern. Neem oil or insecticidal soap, both of which you can get from Amazon, can help with these pests.

Frequently Asked Questions

Zinnia Care Must-Haves