How to grow zinnias from seed?

Zinnia is one of the most popular cut flowers among flower growers, and its blooms are very beautiful, colorful, and long-lasting as cut flowers. Growing zinnias from seed doesn’t require much experience or special knowledge, so it’s well-suited even for beginners. Growing zinnias from seed is also successful in Finland and in northern conditions. Here are the best tips and instructions for how to grow zinnias from seed.

Zinnia seeds

Zinnia seeds are usually small, dark, and flat, and may have a slightly glossy surface. The seeds can range in color from dark brown to black and may be round or oval in shape. Some zinnia seeds can also appear a bit wrinkled or uneven, but this usually doesn’t affect their germination or growth.

Zinnia seeds can be purchased at most garden stores or ordered from online seed shops. Some popular zinnia varieties include: Giant zinnia ‘Zinderella Peach’, Giant zinnia ‘Zinderella Lilac’, Giant zinnia ‘Benary’s Giant White’, Giant zinnia ‘Isabellina’, Giant zinnia ‘Oklahoma Salmon’, Giant zinnia ‘Oklahoma White’, Giant zinnia ‘Queen Lime Blush’, and Giant zinnia ‘Queen Red Lime’.

Some popular zinnia varieties

Zinnia elegans ‘Queen Red Lime’
Zinnia elegans ‘Oklahoma Salmon’
Zinnia elegans ‘Oklahoma White’
Zinnia elegans ‘Peaches and Cream’
Zinnia elegans ‘Polar Bear’

Zinnias can be sown directly outdoors, but it’s best to wait until the risk of frost is over and the soil has warmed up enough. However, it’s recommended to start the seeds indoors in seed-starting soil so that they bloom earlier in the summer, especially since the Finnish summer is short. Sow the seeds in moist soil at a depth of about 2–3 mm. The seeds can be covered with a thin layer of soil or vermiculite. In general, late April and May are good times to sow zinnia seeds.

Starting zinnias indoors is recommended, as it speeds up growth and improves blooming. The indoor growing period is about 4–6 weeks before planting out. Sow the seeds in pots placed in a bright spot or under grow lights as soon as they have germinated. Sufficient light is important to prevent the zinnias from becoming leggy and to help them develop into strong plants before it’s time to move them outdoors. Make sure the plants get enough water, but not too much. After a couple of weeks, you can start giving the small plants a bit of liquid fertilizer for seedlings.

When the zinnia seedlings have grown a bit larger, it’s a good idea to prick them out, meaning transplant them into larger pots or separate them into individual pots. This helps the plants develop a better root system and gives them more space to grow.

It’s also good to pinch the zinnia once during the indoor growing phase. Pinching is a way to keep the plant compact and bushy. It involves cutting off the top part of the plant, which encourages it to branch out and grow more densely. Pinching is usually done when the plant is about 10–15 centimeters tall. It’s best to do this before flower buds form so that pinching doesn’t delay blooming.

Invest in a good pair of pruning shears to make pinching easier.

In May, you can start hardening off the zinnias by taking the plants outside daily on the balcony or outdoors. The plants can also be planted out when night temperatures stay at a minimum of +10 degrees Celsius.

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Zinnias thrive in a sunny spot with well-drained soil. Add a bit of fertilizer, but make sure they don’t get too much. Plant the seedlings about 20 cm apart. Zinnias can also be planted in pots or hanging baskets. The plants are ready to be planted out when they are about 5–10 cm tall and have 2–3 leaves. This is usually in June or after Midsummer, once the last night frosts are over.

It’s good to water zinnias regularly, but avoid letting the soil become too wet. Too much moisture can make the plants susceptible to mold and fungal diseases. During dry periods, zinnias should be watered manually.

After blooming, it’s a good idea to remove wilted flowers so the plant can focus its energy on forming new buds. Zinnias often bloom well into autumn.

Zinnia is a beautiful and easy-to-care-for cut flower that many successfully grow from seed. By carefully following the sowing instructions and making sure to water and fertilize regularly, you can enjoy zinnia’s beautiful blooms all summer long.