Centaurea nigra purple flower, animated real photograph adapted from AnemoneProjectors, CC BY-SA 2.0: https://commons.wikimedia.org/wiki/File:Common_Knapweed_(Centaurea_nigra)_(20078030555).jpg ; license https://creativecommons.org/licenses/by-sa/2.0/

Centaurea nigra purple flowers and upright perennial growth

Centaurea nigra flower detail, upright growth and meadow-style border illustration

Centaurea nigra sowing, establishment and flowering guide

Centaurea nigra Seeds

Size

30-day money-back guarantee

Fast Shipping

High Quality

Secure

Grow Guides

About the Variety

Centaurea nigra, commonly called common knapweed, brings purple-pink flower heads and an informal meadow character to the garden. Dark overlapping bracts frame each bloom, while upright, branching stems rise above narrow green foliage. This herbaceous perennial attracts visiting bees and butterflies.

Key Features

Purple-pink, thistle-like flower heads
Upright perennial growth
Summer to early-autumn flower interest
Flowers visited by bees and butterflies

Plant Details

Botanical Name	Centaurea nigra
Common Name	Common knapweed
Life Cycle	Herbaceous perennial
Light Requirement	Full sun or partial shade
Bloom Season	Summer to early autumn; timing varies with climate
Growth Habit	Upright, branching stems
Plant Height	Approximately 30–100 cm (12–39 in), depending on conditions
Flower Color	Purple to pink-purple
Foliage	Narrow green leaves
Soil	Moist, well-drained soil
Hardiness	RHS H6; suitability depends on local conditions
Pack Option	1 Pack
Seed Count / Coverage	Refer to the supplied seed packet

Planting Information

Planting Season	Spring or autumn, according to local conditions
Sowing Method	Seeds may be started indoors in a moist, well-drained seed-starting mix or sown directly into prepared soil where cultivation is permitted.
Planting Depth	Sow approximately 1/16–⅛ inch (2–3 mm) deep. Cover lightly with fine soil and avoid deep planting.
Germination	Approximately 7–21 days at 59–68°F (15–20°C) under favorable conditions. Germination may be uneven.
Water Needs	Keep the seedbed moist during establishment; avoid waterlogging
Plant Spacing	Allow approximately 12–16 inches (30–40 cm) between mature plants where cultivation is permitted.
Flowering Time	Depends on sowing date, climate and establishment

SAVE ON SELECT FALL SEEDS

Select Fall Seeds are on sale now. 🍂

Shop Fall Seeds on Sale

FAQs

How do you ship?

Seeds ship after a handling period of 3-5 business days, with most orders arriving within 10-15 business days from there.
Once your order leaves our warehouse, you'll receive a shipping confirmation email with tracking — so you know exactly where things stand.

Are your products GMO?

All of our seedsare non-GMO. We've made that commitment as our Safe Seed Pledge.

Are your seeds treated?

Most of our seeds are untreated. Some varieties are coated with a fungicidal treatment to support germination and early establishment, particularly in challenging growing conditions. If a variety has been treated, it will be clearly noted on the product page and packaging.

How Should I Store Unused Seeds?

Our recommendation is to buy for the season you're planting. But if you have seed left over, proper storage keeps it viable longer than most people expect.

To store unused seeds:

1. Seal them in an airtight container or plastic bag to protect against moisture and insects
2. Keep them somewhere cool, dark, and dry — away from sunlight and humidity
3. Skip the refrigerator; fluctuating moisture is harder on seed than temperature

Stored well, most seeds hold through the following growing season with excellent results. Our seeds typically lose less than 5% of their viability per year under ideal conditions.

Not sure if older seed is still good? A quick germination test will tell you:

Moisten a paper towel, place 10 seeds on one half, fold it over, and seal it in a plastic bag or airtight container. Keep it in a warm location appropriate for the variety, and check periodically over the seed's normal germination period. Count how many sprout — 8 of 10 means roughly 80% viability. If the rate is low, you can often compensate by sowing more thickly. Just keep in mind this measures viability under ideal conditions, so actual garden performance can vary with soil, moisture, and weather.