When Should I Plant Giant Sunflowers?

Mammoth sunflowers are giant sunflowers that turn east in the morning and follow the sun across the sky. They grow heavier as they grow, with their heads becoming heavier with seeds and soil. The ideal time to plant mammoth sunflower seeds is late spring or early summer when the soil has warmed up and there is no longer a risk of frost. This will provide optimal flowering throughout the season.

To plant mammoth sunflowers, plant seeds about 1 inch deep and 6 inches apart, covering them with soil. Rows should be 30 inches apart. You’ll thin out most of the seedlings, but initially planting a small amount will help. Mammoth sunflowers typically reach maturity and are ready for harvesting approximately two months after planting.

Choosing the right location for planting mammoth sunflowers is essential. Mammoth sunflowers require full sun, so sow them earlier as all danger of frost is past and night temperatures are above 50 degrees Fahrenheit both day and night. In shorter-season, cold winter areas of the U.S., this means late May to early June.

Sunflower seeds germinate in 7 to 14 days, and you can plant them anytime, but make sure they’re inside until about halfway through spring. You can also buy a sunflower head from a farmers’ market.

Sunflowers can be grown year round in Zones 9 and 10, but are most happy in the warm season. Direct sow seeds in the spring once soils have warmed.

Is a mammoth sunflower a perennial?

Helianthus giganteus is a perennial herbaceous plant with slender, lanceolate leaves and bright yellow flower heads. It is typically found in valleys with wet meadows or swamps, growing up to 4 meters tall.

How long does it take for mammoth sunflowers to bloom from seed?

Sunflower varieties can mature quicker than others, with fast-growing varieties like ‘ProCut Red’ and ‘Ruby Eclipse’ blooming just 55 days after planting, while giant types like ‘Mammoth Grey Stripe’ can take 120 days. Sunflower seeds typically mature about one month after the flowers open, so if your sunflowers bloom in August, they are usually ready to harvest in September. Sunflower seeds are fully ripe when the flower head droops and turns backward on itself, turning golden brown and having well-formed shells.

What is the best month to plant sunflowers?

Sunflower seeds should be planted directly into the garden after spring frost has passed and soils have warmed to at least 50°F (10°C), which occurs between April and mid-June in the northern half of the U. S. and Canada. Sunflowers are heat-tolerant, resistant to pests, and attractive to pollinators. They can be harvested in late summer and fall for a healthy snack or feed to birds. Sunflowers are annual plants with a daisy-like flower face and come in various colors, but are commonly bright yellow with brown centers.

They make excellent cut flowers and attract bees, birds, and butterflies. Sunflowers are heliotropic, turning their flowers to follow the Sun’s movement across the sky and returning at night to face the east, ready for the morning sun.

Should you soak mammoth sunflower seeds before planting?

Soaking seeds before planting is a common method to improve germination, as seeds have a hard outer layer to protect themselves from insects and diseases. Soaking them in water softens the hard seed coat, exposing the embryo to moisture and promoting growth. Sunflower seeds don’t need to be soaked, but soaking them for 12 to 24 hours can hasten germination and increase the number of sprouts. To grow sunflowers outdoors, cover the planting area with finished compost or aged manure, then work it into the ground, loosening the top 12-18 inches of soil. This loose soil allows the sunflower’s long taproot to grow easily and improves water infiltration.

Is June too late to plant sunflower seeds?

Early June is the optimal time for sowing sunflower seeds directly into the soil and transplanting baby sunflower plants outdoors. Sunflowers grow large, tall, and cheerful flower heads that brighten and animate your yard. They are beautiful, easy to cultivate, and attract beneficial pollinators. Experts explain how to plant, grow, and care for sunflowers, as well as harvest their seeds for a summer snack. Direct sowing occurs when the risk of frost has passed in late spring.

Space should be kept in mind for the variety of sunflowers, with regularly-sized sunflowers growing anywhere from 8 to 12 inches apart, and jumbo-sized sunflowers needing 16 to 20 inches of space to thrive.

Do mammoth sunflowers transplant well?

When planting sunflowers, ensure they are placed in their permanent location due to their taproot, which makes moving them difficult. However, you can transplant sunflower seedlings from a starting pot, and it is best to do so shortly after sprouting. Move sunflower plants from the sprouting container into the ground less than three weeks after planting or as soon as leaves develop. Leave the plants in the starting container too long, as this may stunt the growth of the long taproot.

What is the lowest temperature sunflowers can tolerate?

Sunflower heads turn yellow as they grow, reducing frost damage risk. At the R7 stage, sunflowers can withstand temperatures as low as -4°C with minimal damage. A frost duration of 6 hours or more below 25°F can cause damage, resulting in losses in yield, test weight, reduced oil content, and discolored seeds. Stage R8 occurs when the backs of the flower heads are completely yellow but the bracts remain green. Frost damage at this stage may result in some reduction in yield, test weight, and oil content, but most seeds are marketable.

Can you plant mammoth sunflowers in July?

In July, it is the last month to sow new sunflower seeds, as most cultivars mature in around three months. Sunflowers grow large, tall, and cheerful flower heads that brighten and animate your yard. They are beautiful, easy to cultivate, and attract beneficial pollinators to your yard. To direct sow sunflower seeds, plant them directly in your outdoor garden when the risk of frost has passed in late spring.

Keep the variety in mind when determining spacing: regularly-sized sunflowers can be planted anywhere from 8 to 12 inches apart, while jumbo-sized sunflowers need between 16 to 20 inches of space to thrive.

Do you plant sunflower seeds point up or down?

To plant seeds in containers, fill them with commercial potting compost and soak the soil. Make a hole about an inch deep with a pencil and drop one seed into the hole. Cover the seeds with a plastic cover or cloche to keep the soil warm and protect them from pests. Keep the soil moist as young seedlings prefer it. Within a few weeks, remove any coverings and you should have small green seedlings. If seed trays were planted, transplant them into larger pots or the ground. Use a small trowel to dig a small hole for the seedlings, placing them no closer than 12 inches apart to allow their roots to grow.

Where should I plant mammoth sunflowers?

Sunflowers require full sun for optimal growth, with 6-8 hours of direct sunlight per day. Choose a well-drained location and prepare the soil by digging 2-3 feet in circumference to a depth of 2 feet. Sunflowers are heavy feeders and deplete the soil more than many other crops, so nutrient supply must be replenished each season. Work in a slow-release granular fertilizer, including trace minerals, about 8 inches deep into the soil. Mix composted rabbit manure and a balanced slow-release granular fish fertilizer, and add organic amendments containing trace minerals like greensand or dried seaweed.

To grow the largest sunflowers, direct sow seed directly into the garden, rather than starting them in pots. Sunflowers have long taproots that grow quickly and become stunted if confined, and peat pots often dry out and block off root growth. Plan to sow seeds in the ground to avoid postponing transplanting.

How close together can you plant mammoth sunflowers?

To grow giant sunflowers, sow them earlier in the summer, as they often flower on shorter stalks. The ideal spacing for these plants is 20 inches apart, with closer plantings resulting in taller stalks but smaller heads, and farther plantings potentially causing larger seed heads. If space is limited, sow in a small clump that will eventually be thinned to one plant.

To sow seeds, water the soil, press seeds 1 inch deep in clumps of 5-6 seeds about 6-8 inches apart, and cover loosely with netting to protect emerging seedlings from birds. Seedlings will appear within 5-10 days if the soil is kept moist. Thin the plants to the most vigorous 3 or 4 when they grow to 3 inches, 2 when they reach 2 feet, and back to the best single seedling when they reach 2 feet high.

Feeding and care for your growing giant sunflowers are essential. Water around the root zone with 2 gallons of diluted liquid fertilizer solution per week while the plant is small. For larger plants, create a doughnut-shaped moat around the plant and pour several gallons of diluted fertilizer into it every week. Avoid pouring fertilizer directly on the stems, as this can cause them to rot.