How to Grow Zinnias from Seed: Sowing, Care and Cutting

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Zinnia seeds may be sown outdoors once frost season ends and the soil is about 70 F, a quarter inch deep. Sown straight into the garden, zinnias come into flower 8 to 12 weeks later, and they are generally quick to grow from seed and need little upkeep. For a head start, sow indoors 4 to 6 weeks earlier and set the seedlings out after frost.

Zinnias rank among the most popular summer annuals grown in the United States. The sections below take them from sowing and care through mildew to cutting; where growing figures vary, a zinnia figure here is given as a span or as two views. For other annuals to sow, see our flowers from seed guide.

Zinnias from seed at a glance

When to sow	After the last frost, with soil around 70 F (some guides wait for at least 70 F)
Depth	1/4 inch
Spacing	Can range from 8 to 24 inches, by plant habit; one spacing table goes as close as 6 inches
Sprouting	4 to 8 days with the mix at 70 to 75 F; 3 to 5 days in soil at 80 to 85 F
First flowers	8 to 12 weeks after direct sowing
Sun	At least 6 hours; the strictest guide asks for 8 or more
Pets	On the poison-control list as non-toxic to dogs, cats and horses

When to plant zinnia seeds

Zinnias are warm-season annuals, and nearly every guide waits for frost to pass before seed goes outdoors: seed can go straight into the garden once the last frost date has passed and spring's danger of frost is over. Zinnias are frost sensitive.

Soil warmth is the second test. Seed goes in once the soil reaches 70 F; one guide calls soil and air around 70 F ideal, and the strictest direct seeds only once the soil is at least 70 F. Transplants can go out a little sooner, once the soil warms to 60 F.

One guide runs earlier. Its seed-starting table marks zinnia with an asterisk, the group it picks for sowing straight into the garden two weeks short of the average frost-free date. In our reading, a soil thermometer settles it: sow at about 70 F soil, after frost. Our frost dates page shows when that usually happens for your area.

How to sow zinnia seeds outdoors

Zinnia seeds are large and quick to germinate, one of the reasons zinnias suit children and beginning gardeners.

1. Pick a spot in full sun with soil that drains well. Give it at least 6 hours of sun; one guide asks for 8 or more. One guide gives zinnias a soil pH of 5.5 to 7.5, while another calls them not picky about pH.
2. Sow 1/4 inch deep, 2 to 3 seeds per foot of row, and cover them lightly with soil. Firm the soil down over the seed to give it good soil contact.
3. Water, then keep the surface from drying out until the seedlings come up. A light fabric such as Reemay over the row helps the seed sprout by holding in moisture and evening out the temperature.
4. Thin when the first true leaves open, or when seedlings are 3 inches tall.

How far apart to thin depends on the plant. Spacing can run anywhere from 8 to 24 inches, closer for single-stalk types and wider for bushy ones. Dwarf cultivars are thinned to 8 to 9 inches and 2- to 3-foot cultivars spaced a foot apart, though one spacing table gives 6 to 12 inches for common zinnia. Cut-flower beds use a 9 by 9 or 12 by 12 inch grid.

Starting zinnias indoors

Starting indoors is for earlier flowers: earlier harvests may come from transplants. Guides differ on how far ahead to start, so the table sets four schedules side by side, each row from one guide.

When to start zinnia seed indoors: four schedules

Start indoors	Germination
About 6 weeks before planting out	4 to 8 days, in darkness, at 70 to 75 F
4 to 6 weeks before the frost-free sowing date	At 65 to 70 F
5 weeks from sowing to planting out	5 to 7 days at 70 F, seed covered
4 weeks before the last frost, and no earlier	3 to 5 days with soil at 80 to 85 F

The four-week schedule stops there because double-flowered zinnias may go back to single flowers when a transplant is root bound or its roots are badly disturbed. Starting too early also usually gives spindly plants.

The indoor method, step by step:

1. Sow 1/4 inch deep in a seed-starting mix and cover with vermiculite; in 72- or 50-cell trays, sow 1 to 2 seeds per cell. Zinnias need darkness to germinate.
2. Keep the mix moist under a plastic cover. A seedling heat mat can warm the tray; drop to about 70 F once seedlings appear, or grow them at 70 to 75 F by day and 65 to 70 F at night.
3. Let the mix dry slightly between waterings to avoid damping off, thin to one seedling per cell, and harden the plants off for a few days in a sheltered spot before transplanting.

Lights, trays and hardening off get more detail in our seed-starting guide. If a tray stays bare, old seed may be why: seed not stored cool and dry often germinates poorly (see our seed storage guide).

Sun, soil, water and feeding

Sun and soil. Zinnias want full sun and fast-draining soil, and they grow most strongly in a very warm spot. They prefer fertile soil rich in organic matter. Compost or sand can help heavy soil drain, and an inch of compost, low in salt, can go into the bed before planting.

Water. Zinnias handle dry spells better than soggy soil. Water only once the top 1 to 2 inches have dried out: excess water can bring on fungal diseases and can lead to root rot. Water at the base, with a soaker hose or drip line where you have one. New transplants take water 2 to 3 times a week; established plants are fairly drought-tolerant and can get by on one watering a week. Guides give 1 inch a week, or 1 to 1.5 inches each time you water.

Feeding. Guides split here. One mixes a balanced fertilizer into the soil at planting, then feeds monthly with one higher in phosphorus than nitrogen. Another calls zinnias moderate feeders, adds nitrogen in general at about 0.15 pounds per 100 square feet a year, half at planting and half later in the season, and applies phosphorus and potassium only when a soil test calls for them. A soil test before fertilizing is recommended either way.

Pinching, staking and deadheading for more flowers

Pinching. Pinch out the center growing point when a plant reaches 8 to 12 inches, taking off the top 3 to 4 inches; the side branching that follows gives more blooms and longer stems. Pinching back leggy plants also encourages fuller growth.

Support. For tall cutting zinnias, string a layer of horizontal netting between 4-foot garden stakes; it can go in at planting and be raised as the plants grow, before buds form.

Deadheading. Deadhead for continuous bloom; deadheading also stops the plant from spending energy on seed. Two exceptions are worth knowing: the Profusion series needs no deadheading because new flowers grow above the old ones, and creeping zinnia does not require it either.

Zinnia types and varieties

Most of the common zinnia varieties trace back to Z. angustifolia or Z. elegans, and a third group is a cross between the two. A flower is single when one row of petals leaves the center in view, and double when many rows hide it.

Common zinnia (Zinnia elegans) is the species grown most, an upright plant with broad, coarse leaves and big flowers. Narrow-leaf or creeping zinnia (Zinnia angustifolia) is low and spreading, with small single flowers, and suits a garden where powdery mildew is a worry. Hybrid zinnia (Zinnia marylandica), which came from crossing the two, makes compact plants with heat, drought and disease tolerance.

Zinnia series and their traits

Series	Height	Traits
Benary's Giant (Z. elegans)	36 to 42 inches, or 3 to 4 feet	Large double flowers on strong stems; developed with cutting in mind, with improved vase life
Oklahoma (Z. elegans)	30 to 40 inches	Double and semi-double flowers about 2 inches across; resistance to powdery mildew and good vase life
State Fair (Z. elegans)	30 to 48 inches	Large flowers; tolerates powdery mildew and Alternaria leaf spot well; the lowest cull rates in one cut-flower trial
Magellan (Z. elegans)	9 to 14 inches	Dwarf, early, large double flowers; rated good to excellent in another university's trials
Thumbelina (Z. elegans)	6 inches	A dwarf for containers and edging
Profusion (Z. marylandica)	12 inches, up to 18	Compact mounds; more resistant to powdery mildew and leaf spot; no deadheading
Zahara (Z. marylandica)	8 to 18 inches	Compact, heat-tolerant, resistant to leaf spot and mildew
Crystal and Star (Z. angustifolia)	Crystal 6 to 8 or 10 to 14 inches, by guide; Star 10 to 14 inches	Low, single flowers; Crystal has good tolerance to powdery mildew

Read the seed packet as well: a scissors icon often marks varieties meant for cutting, and a packet can usually tell you whether a cultivar still carries pollen and nectar for pollinators, a trait bred out of some zinnias. Many varieties have double flowers, which offer little or no pollinator value; in general, Z. angustifolia types bear single flowers and Z. elegans typically double ones.

Powdery mildew and other zinnia problems

Powdery mildew comes up in nearly every zinnia guide we read. Many zinnias are affected, especially in humid weather, and one guide calls them highly susceptible. It shows as a white film that looks as if the leaves were dusted with flour.

Prevention, where the guides agree:

• Grow resistant types. Look to narrow-leaf zinnia, the Zahara and Profusion series and, among the tall cutting types, the Oklahoma series, and choose mildew-resistant varieties in general.
• Leave room for air. Space plants for air circulation; moving air helps dry the leaves.
• Keep leaves and splash down. Avoid wet foliage. Mulch, and water near the root zone with soaker hoses, drip lines or a hand-held hose to limit soil splash that may carry spores.
• Clean up in fall. The fungus overwinters mainly in leaf debris or dormant buds, so remove infected plant material at season's end, keep it out of the compost bin and clean snips in a mix of one part bleach and four parts water.

One guide differs on watering: its disease table says sprinkler irrigation reduces powdery mildew compared to drip irrigation. Other guides tie wet leaves to the leaf spot diseases, so in our reading watering at the base remains the default for a home bed.

For treatment, use neem oil or a fungicide according to the label directions; a fungicide can treat mildew or protect plants. One guide lists a copper fungicide while noting that spraying may not be worth it late in the season. We do not recommend a particular product; read the label of any spray.

Other zinnia problems and what to do

Problem	What you see	What to do
Alternaria leaf spot	Big spots, reddish brown or purple, whose gray or tan centers may fall out	Keep leaves dry; the disease is seedborne, and a fungicide is listed for it
Root, stem and crown rots	Dull foliage or wilting, then yellowing; dark, soft roots	Too much water can bring on rot, so water less; plant in well-drained soil or raised beds
Aphids, thrips, spider mites	Sticky honeydew; stippled leaves; deformed petals	Natural predators, water sprays, and insecticidal soaps or oils for most situations

For aphids on any garden plant, see our aphids guide.

Cutting zinnias for a vase

Zinnias are often treated as a foundation of the cutting garden. Harvesting blooms encourages more of them, and cutting deep, 2 to 4 nodes below the flower, encourages long stems to grow back.

When to cut. Most guides cut in the morning or the cool of the day, before the heat sets in, when the air is cooler and the stems are well hydrated. One cut-flower garden guide runs the other way and cuts in the late afternoon or evening. In our reading, all of them keep clear of midday heat.

Which flowers. Pick flowers with centers just starting to open. Another sign: two or more full rows of petals have opened and the top of the stem is mostly stiff; a flower cut too early will soon droop.

How to cut. Cut just above a leaf node using sharp, clean scissors or pruners, which encourages new buds and avoids brown stubs. Put the cut stems straight into a bucket of water.

For the job, we pick the Corona FS 3214D Micro Snips; our pruning shears buying guide, which compares more pruners, picks them for soft harvest stems, herbs and flowers. Their 1 3/4 inch blades are stainless steel and double-beveled, and the tapered tips are made for trimming, deadheading and harvesting. A lock for either hand and a heavy-duty spring round them out.

More in our shop: harvest tools.

Keeping them fresh. Strip the lower leaves before the stems go into water. Use room-temperature water in the vase and change it every 2 to 3 days. A tablespoon of chlorine bleach per gallon of bucket water helps against bacteria, and the stems should not be stored below 40 F. Expect about a week to 10 days in the vase for most varieties, sometimes up to 2 weeks.

Are zinnias toxic to cats and dogs?

In its animal poison control database, the ASPCA lists zinnia (Zinnia species) as non-toxic to dogs, to cats and to horses. Still, dogs and cats that eat plant material of any kind may throw up or have stomach upset.

One naming trap. The "creeping zinnia" on the dog and cat poison-control lists is Sanvitalia, a different plant from the creeping zinnia (Zinnia angustifolia) in the varieties section above, and it is filed under non-toxic plants too. If you think your pet is ill or may have eaten something poisonous, get help from your veterinarian or from the ASPCA's poison hotline, (888) 426-4435, which is open 24 hours.

What you'll need for zinnias

Picks on Amazon

• Corona FS 3214D Micro Snips Check price on Amazon

Sources we used

Every zinnia figure above was taken from the extension, ASPCA and Corona pages below, each saved when read in October 2026; if two of them disagree on a zinnia number, the text carries both or the full span.

• "University of Minnesota Extension: Zinnia" (reviewed 2026)
• "UW-Madison Extension, Wisconsin Horticulture: Zinnias" (revised 2026)
• "Clemson Cooperative Extension HGIC 1149: How to Grow Zinnias" (2025)
• "Utah State University Extension: Zinnia Cut Flower Production in Utah" (2020)
• "Illinois Extension: Zinnia", "Prevent, protect zinnias from powdery mildew" (2025), "Garden Scoop: Zinnias" (2021), "Homegrown bouquets: three species for your garden" (2024) and "Start to Finish: Growing a Cut Flower Garden" (2020)
• "NC State Extension, Plant Toolbox: Zinnia elegans"
• "Penn State Extension: Zinnia Diseases" (2025), "Sowing Annual Seeds" and "Growing Cut Flowers for Joy"
• "Iowa State University Extension: Germination Requirements for Annuals and Vegetables"
• "Colorado State University Extension: Growing Annual Plants from Seed"
• "ASPCA Animal Poison Control: Zinnia" and its toxic and non-toxic plants list, with its plant lists for dogs and for cats
• Corona's product page for the FS 3214D Micro Snips, for their specifications

Related guides

• Flowers from seed, the other annuals to sow for beds and a cutting garden.
• Sunflowers, another warm-soil annual to sow straight into the garden.
• Starting seeds indoors, for a head start on zinnias before the last frost.
• Pruning shears, for clean cuts on flower stems.

Frequently asked questions

When should you plant zinnia seeds?

Wait until the last spring frost is behind you and the soil reaches around 70 F; some guides wait for soil of at least 70 F. To start them indoors, sow 4 to 6 weeks before that outdoor date.

How deep do you plant zinnia seeds?

Plant them 1/4 inch deep and firm the soil over them. Zinnias need darkness to germinate, so cover the seed.

How long do zinnias take to grow from seed?

At 70 to 75 F, seed sprouts in 4 to 8 days. Zinnias sown directly in the garden come into flower 8 to 12 weeks after sowing.

Should you start zinnias indoors or sow them directly?

Either works. Zinnias generally grow quickly enough that they can be direct seeded once frost has passed. Transplants may flower earlier, but keep indoor starts short: root-bound doubles may revert to singles.

How do you keep powdery mildew off zinnias?

Grow resistant types such as the Zahara, Profusion or Oklahoma series, and space plants for air flow. Keep the leaves dry and clear infected plants away in fall. For treatment, use neem oil or a fungicide by the label.

Do zinnias come back every year?

Common zinnia is an annual, so you sow it again each spring; one perennial exception is prairie zinnia (Zinnia grandiflora), hardy to zone 4a. Seed saved from the previous year's garden may not give predictable results.

Are zinnias toxic to cats and dogs?

In its poison control database the ASPCA lists zinnia as non-toxic to dogs, to cats and to horses. Still, dogs and cats that eat plant material of any kind may throw up or have stomach upset, so call your veterinarian if a pet seems unwell.