How To Grow Zinnias (Complete Guide)

If you’re looking for a massive bust of color in your garden from low-maintenance flowers, you should consider growing zinnias. Zinnias are beautiful flowers that grow quickly and bloom heavily throughout the summer. They’re easy to grow and can magnificently decorate your garden, terrace, or balcony with vibrant colors like red, pink, orange, green, yellow, and white.

Zinnias belong to the Asteraceae family and are closely related to sunflowers and daisies. They’re perfect for cutting gardens and require minimal care, making them excellent for new gardeners and nurturing your kid’s green thumb. Zinnia seeds only require basic garden preparation to sprout, and the plant can flourish and flower in a few weeks with little fertilizer. 

They’re heat and drought-tolerant, and their brightly-colored blooms easily attract butterflies, bees, and ladybirds. Read on to learn how to grow zinnias and add color to any outdoor space. 

Zinnia Quick Facts

Common Name	Zinnia
Scientific Name	Zinnia elegans
Plant Type	Annual
Size When Mature	6-18 inches wide, 1-4 feet tall
Sun Exposure	Full
Soil Type	Well-draining
pH of Soil	Neutral
Blooming Time	Summer, spring, fall
Color of Flowers	Red, pink, orange, green, yellow, white
Hardiness Zones	3-10 (USDA)
Nativity	North America, Central America, South America

Planting Zinnias

You can plant zinnias in various ways, including sowing seeds directly into the ground, sowing seeds in pots or containers, or planting out plug plants. Sowing directly usually reaps the best results because zinnias don’t like root disturbance or getting transplanted. Direct sowing ensures the root system is not disturbed, promoting growth and development. 

Where to Plant Zinnia Seeds

Choose a location with full sun of around 6 to 8 hours per day to get plentiful blooms. Although zinnias can adapt to most soil conditions, well-draining, rich soil is ideal. Zinnias can grow even in bad soil, but adding some compost or humus can boost the plants and help them grow quickly if the soil is poor. 

Zinnia roots can’t tolerate damp soil, and excess moisture can lead to rotting or fungal infections. Neutral soil pH is ideal and can be between 5.5 and 7.5. You can also start zinnia seeds in small pots, but taller varieties will require larger pots or containers, or you may need to transplant them to the garden while young and do so carefully.

If you’re sticking with container gardening, consider hybrid zinnias that usually grow short in a spreading habit. 

When to Plant Zinnias

The most widely grown variety of zinnias originate from Central America and Mexico and thrive in warm climates. Zinnias are very sensitive to cold or frost, so you must wait until all the chances of frost have passed in your area and the soil has warmed in early summer to sow or transplant. 

A rule of thumb is to wait until around May in Northern US or early July in cooler climates. Zinnias usually start to grow or germinate when the minimum daytime temperature reaches around 16o°C or 60o°F. 

How to Plant Zinnias

1. Start by getting the seeds. Most garden centers sell zinnia seeds, and you can even get a beginner-friendly bag of zinnia mix seeds which features a mixture of seeds, soil improvement, and fertilizer. 
2. Find a sunny spot with well-draining soil. 
3. Prepare the soil by cleaning out debris and raking it well so the roots can grow easily. Mix the soil improvement or other organic matter and compost into the soil to help the seeds get off on a strong start.
4. Once the soil is ready, directly sow the seeds where you want them or sprinkle over the soil’s surface, gently press them into the top layer, and cover them with mulch or organic material. 
5. The seeds should only be ¼ of an inch deep and planted 6 inches apart within a row with around 2 feet between the rows. Some larger varieties need to be planted at least 12 to 18 inches apart for proper air circulation and disease prevention, so check your seeds packet for more accurate spacing information. 
6. Water the soil after planting and ensure the soil stays moist but not saturated until the seeds germinate. 
7. Seedlings can start popping out in 4 to 7 days for most varieties, but it can take several weeks to a few months for blooms to appear, depending on the weather or climate conditions. 

Caring For Zinnias

Caring for the zinnia plant is extremely easy, and ensuring it receives sufficient water and nutrients after emerging from the ground is important.

Watering

Young zinnia plants need moist soil to grow at their best and stay healthy.

Insufficient watering can result in small plants with few blooms, so ensure you water the plant at least once a week but avoid saturating the soil. Continuous wet conditions or overwatering can lead to rot and fungal infections like powdery mildew and leaf spots. 

Zinnias are relatively drought-resistant once established, but moderate soil moisture can help maximize growth. Add water when the top soil feels dry, and aim to water the plant at the base instead of overhead to ensure the leaves and foliage don’t get wet.

Always water your zinnias in the morning to ensure the leaves dry out during the day. Watering in the evening can leave the foliage moist for long periods and increase the risk of fungal infections. 

Fertilizing

As low-maintenance plants, zinnias only require occasional feeding with a well-balanced fertilizer. When planting, incorporate a light general-purpose fertilizer with phosphorus, nitrogen, and potassium.

A side dressing of organic fertilizer at flowering can help produce bigger and more numerous blossoms. Follow the seed packet instructions to determine the amount to use. 

Compost and mulch can also make a difference and help the plant perform better. You can sow the seeds directly into one or two inches of organic mulch to give them nutrients throughout the season. 

Thinning

Thinning seedlings is important to reduce competition for resources, allow sufficient air circulation, and prevent diseases from spreading, especially if you scatter the seeds when planting.

Thin out your zinnia seedlings once they grow to around three inches tall to ensure they’re placed six to 18 inches apart, depending on the variety. 

You can determine which seedling to thin depending on its fitness. Simply thin out the weakest seedlings that are either too leggy or tall, stunted or short, or don’t look as healthy as the others.

Thinning also makes it easier to weed the zinnias when they get bigger and gives the roots and leaves enough space to grow and flourish. 

Pruning and Deadheading

Pruning your zinnias regularly can promote growth and help them thrive. The key to getting long stems is to prune your zinnias while they’re still young.

Simply snip off 3 to 4 inches from the top of the plant just above the set of leaves using sharp pruners when the plant reaches 8 to 12 inches tall. The plant will produce more stems from the point of the cut, resulting in longer stems and a healthier display of blooms. 

Deadheading involves cutting off old flowers to encourage more flowers to form, and it can help produce brilliantly colored blooms.

Simply locate the wilting or brown flowers and cut them off individually using shears, garden clippers, or scissors. Take care to get enough of the stalk and avoid cutting off big portions of the plant. 

Disease Control

Fungal and bacterial diseases like powdery mildew and leaf spots can affect zinnias, especially if the leaves stay wet for longer.

Powdery mildew appears as a grayish-white powdery coating on the plant foliage and can also infect the stems and flowers. Leaf spots start as small circular spots that rapidly expand and become irregularly shaped, eventually falling out or tearing and leaving holes in the leaves. 

Good cultural methods like soil preparation, optimal plant spacing, mulching, irrigation, fertilizers, and adequate sunlight can help prevent disease problems.

Fungicides can also effectively control diseases, and you should spray the plants weekly in the evenings to reduce the impact on pollinating insects. 

Keep the foliage dry to discourage fungal and bacterial diseases and remove any disease-infected plants or plant debris to prevent disease spread. Seeds can also be infected and spread diseases, so avoid saving seeds for sowing if there is an outbreak of spot diseases. 

Pest Control

Zinnias are affected by insect pests like spider mites, aphids, and whiteflies that can damage plants, especially in hot and dry weather.

Using insecticides, apart from insecticidal soap, is discouraged for controlling mites and pests because zinnias are excellent nectar and pollen sources for many beneficial insects and hummingbirds. 

Practicing good cultural methods is better for prevention. You can also hose off spider mites and aphids using a strong water stream or reduce the hot and dry conditions that mites thrive on through supplemental irrigation to prevent infestation.

Insecticidal soap can also help control pests by spraying it on the lower leaf surface where they feed, but you should do it in the late evening to reduce harm to beneficial insects. 

How To Grow Zinnias In Pots

Zinnias are heat-loving flowers and can adapt well in pots and containers, provided you provide the right environment for their needs.

You can grow zinnias in pots by direct sowing or by starting the seeds indoors and transplanting the seedlings into a container or pot. 

Direct Sowing

• Choose a suitable container for the zinnia variety you’re planting and ensure it’s big enough and has good drainage holes. Taller varieties do well in larger pots with extra support at the base of the plant. 
• Fill the pots with good quality soil mix and plant the seeds approximately ¼ inch deep with a 6 to 8 inches spacing. 
• Cover the seeds with the soil mix and water well, ensuring the soil stays moist but not saturated as you wait for the seeds to germinate. 
• Move the pot to a sunny area and water the zinnias regularly, feeding them with a liquid fertilizer every few weeks during the summer. 

Starting Seeds Indoors

Starting seeds indoors can help you get a head start on the growing season as you wait for temperatures to get warmer by allowing you to transplant larger seedlings instead of planting seeds.

• Find suitable peat pots, jiffy pellets, or lengths of guttering to sow your seeds separately. This helps prevent root disturbance and minimizes handling during transplantation. 
• Fill them with soil mix and sow the seeds, then cover them with the mix. 
• Add water and keep the soil moist until the seeds germinate for the best results. 
• Place the pellets or peat pots on a heat mat or propagator to help warm the soil and aid in germination. 
• Once the seeds have germinated, remove the peat pots or jiffy pellets and grow them under a growing light until they’re ready to be planted into the pots. 
• Harden off the young plants before transplanting for 7 to 10 days to allow the plants to get stronger and acclimatize to changes in wind, temperature, sunlight, and rain. 
• Once the temperatures are warmer, transplant the seedlings into the pots following the spacing guidelines in the seed package and water them well. 

Caring for potted zinnias is easy, and as long as you provide the right environment to meet their needs, they’ll reward you with beautiful blooms all summer. 

How To Grow Zinnias From Cuttings

You can also duplicate your favorite zinnias by growing them from cuttings:

• Cut around 2 ½ to 3 inches of stem and leaf and put it in a small pot.
• Add a mixture of compost and grit into the pot and water well, and ensure it’s not waterlogged.
• Place in a warm spot like a windowsill or a greenhouse.
• The cutting will start growing roots in two to three weeks, and you can transplant it to a bigger pot or garden. 

Conclusion

Anyone can grow zinnias and have them flourish without breaking a sweat, and they’re a fun way to add color to your garden or any outdoor space. They’re excellent at attracting pollinators like butterflies, and you can plant them with your vegetables or as cottage garden plants, prairie plants, wildflower meadows, or cutting garden flowers.

Try them out this year and enjoy vivid colors that can brighten up any area!