Sowing and Planting Sunflowers: Tips for Growing and Companion Planting

Growing Sunflowers: What You Need to Know

Sunflowers (Helianthus) form their own genus within the aster family (Asteraceae). In addition to annual varieties such as the common sunflower (Helianthus annuus), there are also perennial varieties that grow more like hardy perennials and tend to produce smaller flowers. The flowering period extends roughly from August to October, but varies greatly depending on the variety and when the seeds are sown.

Although sunflowers are native to South America, they now grow naturally across much of Europe. After being brought to Europe by Spanish sailors, people discovered that they are very useful plants. Sunflowers were soon cultivated in Russia and throughout Eastern Europe for oil production.

The Right Location

Sunflowers are quite hardy and can grow in humus-rich clay soils as well as in slightly acidic sandy soils. However, they are heavy feeders, meaning they require a lot of nutrients, especially if they are to produce many flowers. For this reason, they usually grow smaller and produce only small flowers in nutrient-poor soils. As the name suggests, sunflowers love the sun and should therefore be planted in a sunny spot. It is also important to note that sunflowers require long-day conditions. This means they are usually sown only after the spring equinox in March. They need long days for good growth.

Sowing Sunflowers: Direct Sowing or Starting Seeds Indoors?

Sunflowers develop deep taproots that can extend up to 2 meters/2.2 yards into the soil. This makes them particularly drought-resistant, but it also means that sunflowers grown from seed often have trouble establishing themselves. As soon as the roots become too long for the pot, they curl up at the bottom of the pot. As a result, the plant stops growing above ground as well, since the development of the taproot is crucial for its overall growth and stability. However, starting them indoors can also have advantages—for example, if you have a lot of snails in your garden. This way, you protect the delicate seedlings from being eaten. You also prevent birds from pecking the seeds out of the soil prematurely.

Here’s What to Keep in Mind When Growing Plants

If you do decide to start them from seed, it’s best to choose extra-deep seedling pots; so-called “seed snails” also work well for this. With biodegradable pots, you can later transplant the seedlings directly into the garden bed without disturbing the roots.

Key Facts About Planting

Instructions for Direct Sowing

1. Soak the seeds in chamomile tea for 24 hours. This softens the seed coat and helps the seeds germinate faster. Chamomile tea also has antibacterial and antifungal properties, which can protect the seeds from pathogens.
2. Between mid-April and May, you can sow sunflowers directly in the ground. Plant the seeds about two to four centimetres deep in the soil. The soil temperature should be around 10 °C/50 °F. Since young sunflower plants are sensitive to frost, they must be covered in case of late frosts.

Starting and Planting Sunflowers: Step by Step

1. Soak the seeds in chamomile tea for 24 hours.
2. Plant the seeds about two centimetres deep in the soil.
3. If necessary, prick out the seedlings. If you don’t know how to do this, you can find instructions for pricking out here.
4. Once the seedlings are about 15–20 cm/6-8 in tall and there is no longer any risk of frost, they can be transplanted outdoors.
5. Harden off your seedlings: Before planting them out, place the pots outside for a few days, a few hours at a time, so they can get used to environmental conditions like sun, wind, and fluctuating temperatures.
6. Plant them outdoors: For giant varieties, maintain a spacing of at least 50 cm/20 in so the leaves get enough light and air. You can specifically control stem length and flower size through planting spacing: The greater the spacing, the stronger the plants and their flowers will be.

Companion Planting With Sunflowers

Sunflowers work well in mixed cropping. Thanks to their tall, upright growth and deep taproots, they pair perfectly with ground-covering and shallow-rooted plants. A popular example of this is the milpa. In this system, sunflowers (or maize) are combined with cucurbits (such as courgette or squash) and climbing beans (often runner beans). The beans can climb up the sunflowers, while the cucurbits cover the ground and provide shade. You can read more about the milpa tradition in the related article.

Table: Good And Bad Companion Plants

Planting Plans for Your Sunflower Companion Planting

We’ve put together a few planting plans to inspire your sunflower companion planting. Another fascinating fact about sunflowers is that their young buds track the sun. It’s only once they reach full bloom that the stems harden, locking the flowers into a fixed position—usually facing East. Here's a pro planning tip: If you plant them on the northern edge of your garden or flower bed, they’ll end up smiling at you later, rather than your neighbours! ;)

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Sunflowers as Green Manure

Sunflowers also make excellent cover crops. Their deep roots loosen the soil to a great depth, and once the plant dies, they serve as food for soil organisms. Another advantage of sunflowers is their rapid growth, which helps suppress unwanted weeds.

Here’s What You Need to Keep in Mind:

• Sow between April and August for green manure.
• Note: Sunflowers are not frost-hardy.
• A dense stand effectively suppresses weeds (about 30 plants per square meter/per 1.2 square yards).
• The planting spacing here is only 15–25 cm/6-10 in.

Growing Sunflowers in Pots

You can grow sunflowers in pots, but the size of the pot plays a major role in determining how tall the sunflowers will grow and how large their flowers will be.

As mentioned earlier, the length of the taproot also determines above-ground growth. Therefore, you should choose a deep pot. Make sure to water the plant regularly so that the soil remains moist at all times. You should also fertilise regularly, as sunflowers are heavy feeders.

An Overview of Sunflower Varieties

When people think of sunflowers, they usually picture the classic giant yellow variety. But the Helianthus genus offers an enormous range—from tiny balcony plants to hardy perennials.

The Different Growth Habits

• Uniflora types (single-stemmed): These varieties produce only a single, usually very sturdy stem with an impressive main bloom. They are ideal as cut flowers or for setting height records in the garden.
• Multiflora types (branched): These varieties branch naturally and produce many smaller flowers on the side shoots. They often bloom over a longer period of time.
  • Tip: If you “prune” a Uniflora variety (cut off the shoot tip at about 30 cm/12 in), you’ll encourage it to branch out. But you’ll need an extra dose of fertiliser to do this!

The “Wild Cousin”: Jerusalem Artichoke

Jerusalem artichokes and sunflowers are close relatives: they both belong to the same genus, Helianthus, as does the common sunflower. Visually, this is immediately apparent from their yellow flower heads, even though those of the Jerusalem artichoke are significantly smaller (about 4–8 cm/1.5 - 3 in in diameter).

Differences & Similarities

• Survival strategy: While the classic sunflower is usually an annual that survives the winter through its seeds, Jerusalem artichoke is a hardy perennial. It retreats into the ground in the autumn.
• The tuber: Jerusalem artichoke forms underground runners that swell into edible tubers. These have a nutty-sweet flavour (similar to artichokes) and contain inulin, which makes them particularly valuable for diabetics. The plant is quite invasive and suppresses many other vegetable plants, which brings us directly to the next point:
• Vigorous growth: Jerusalem artichoke grows extremely vigorously and can quickly become a “nuisance” in the garden if not contained, as every forgotten tuber fragment will grow into a new plant up to 3 meters/3.3 yards tall the following year.

When and for How Long Do Sunflowers Bloom?

The yellow, orange, or red flowers usually bloom between July and October. Each flower lasts about two weeks, though there are also varieties that produce several flowers at once.

Gardening Tips from Fryd

Practical Tip

Gardening Tips from Fryd

If you sow your sunflowers in stages, you’ll have a longer flowering period. Since flowering is determined by the accumulated heat, plants sown later will bloom sooner than those sown earlier. To extend the flowering period, you can pinch back branched varieties in June. Cutting off the main tip delays flowering and encourages the plant to produce more flowers at the same time.

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Sources

• Hortipedium, 2025: Growing Sunflowers; accessed online on April 10, 2026 at https://www.hortipendium.de/Kultur_von_Sonnenblumen
• Hortipedium, 2025: Sunflowers as a green manure crop; accessed online on April 10, 2026 at https://www.hortipendium.de/Sonnenblumen_als_Gründüngspflanze