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Tuber
Asteraceae
Giant Dahlia 'Manhattan Island' (Dahlia)
Dahlia × pinnata
Manhattan Island produces 15.5 cm (6 in) double decorative flowers, deep red with a greenish-yellow base, on an upright clump 90 cm (35 in) tall. The Van Noort No. 1 tuber should be planted 10 cm (4 in) deep, in full sun, in fertile, well-drained, humus-rich soil. Install support early, pinch the shoots, water deeply at the base, and remove spent blooms until frost. This Dinnerplate variety is suitable for flowerbeds, large pots, and bouquets. In Quebec, lift the tuber in autumn and store it in a cool, dry, frost-free place. Its purplish-red reverse enriches every composition. Its blooms generously renew from July until the first frosts.
- Quantity
- 1 tuber
- Exposure
- Sun
- Life cycle
- Tender perennial
- Hardiness
- Zone 8
Discover the plant
Common nameGiant Dahlia ‘Manhattan Island’
FamilyAsteraceae
GenusDahlia
TypeTuber
Botanical nameDahlia × pinnata
Giant Dahlia 'Manhattan Island' (Dahlia). Giant Dahlia 'Manhattan Island' (Dahlia) The giant dahlia 'Manhattan Island' produces large decorative flowers where deep red dominates, brightened with greenish-yellow at the base of the florets. The reverse side takes on an even darker purplish-red hue, which accentuates the depth of the capitulum when viewed from the side. The international register indicates flowers that can reach approximately 15.5 cm (6 in). Van Noort's No. 1 tuber forms an upright clump about 90 cm (35 in) high and 50 cm (20 in) wide, with green foliage. In summer and autumn, buds succeed one another until the first frost.
This Dinnerplate variety creates a warm focal point in sunny beds, cutting gardens, and large containers. Plant 'Manhattan Island' in spring after the last frost, when the soil has warmed up. Lay the tuber 10 cm (4 in) deep, bud side up, in fertile, humiferous, fresh, and freely draining soil. Leave 50 cm (20 in) around the crown, choose full sun, and protect the clump from strong winds. Install a stake at planting to support the flower heads after rain. Water sparingly before emergence, then deeply at the base when the surface dries. Pinch the young shoot at 20 to 30 cm (8 to 12 in) to encourage branching.
Mature compost and moderate fertilization, richer in potassium at budding, support strong stems and clear coloration without excess tender foliage. Combine 'Manhattan Island' with golden rudbeckias, midnight blue salvias, cream zinnias, and coppery grasses to extend its red and yellow palette. Harvest almost open stems early in the morning, then continuously remove spent flowers to stimulate subsequent buds. To obtain a larger flower, keep the terminal bud and remove the lateral buds. After the first frost in Quebec, lift the tuber, let its surface dry, label it, and store it in a cool, dry, dark, and frost-free place. Check it monthly until the next spring planting.
Planting guide
Plant well.Grow beautifully.
Planting depth
10 cm (4 in)
Best planting time
Spring, when the ground warms up
Propagation
Division of tubers, each bearing a viable bud
Growing method
After the last frost, loosen a sunny area to a depth of 12 inches (30 cm) and incorporate mature compost. Place the tuber horizontally 4 inches (10 cm) deep, bud side up, then leave 20 inches (50 cm) around the crown. Backfill without compacting and only water if the soil becomes dry before emergence. Pinch the shoot 8 to 12 inches (20 to 30 cm) above a pair of leaves. Immediately install a sturdy stake. When growth accelerates, water deeply at the base and fertilize sparingly, favoring potassium for the buds. Tie the stems with soft ties, harvest flowers when almost open, and remove spent flower heads. After frost, cut the stems, lift the tuber, let its surface dry, and store it in a cool, dry, frost-free place. The deep red contrast with a yellow base remains sharper when the plant receives at least six hours of direct sun and regular feeding without excess nitrogen. An early-installed stake supports the 6-inch (15.5 cm) flower heads after rain without compressing the stems or damaging active roots. Remove faded flowers before seed formation so that the clump directs its energy towards new buds until the first frost.
Soil and care
The right care,at the right time.
Soil pH
Slightly acidic to neutral
Minimum temperature
5 °C (41 °F)
Care level
Easy
Watering
Water regularly to keep the soil moist without overwatering. An organic mulch helps retain moisture during hot spells. Water sparingly before emergence, then deeply at the base when the surface is dry. After the first frost in Quebec, lift the tuber, let its surface dry, label it, and store it in a cool, dry, dark, and frost-free place.
Soil type
Prioritize a humus-rich soil that retains moisture while allowing excess water to drain. Check the drainage after rain: water should be able to leave the root zone. Work the soil when it is dry to avoid compacting it. Adapt amendments to its actual texture. In containers, use appropriate potting soil and a pot with drainage holes. Keep these openings clear and avoid any accumulation of water in the saucer.
Fertilization
Incorporate mature compost before planting. At the start, use a balanced formula low to moderate in nitrogen, then favor more potassium when buds appear. Respect the indicated dosage and then water. Too much nitrogen produces tender stems and fewer flowers. The deep red to yellow base contrast remains sharper when the plant receives at least six hours of direct sun and regular feeding without excess nitrogen.
Seasonal care
In spring, inspect the tuber, remove only rotten tissue, and plant after the last frost in warmed soil. Install support immediately. Until emergence, avoid repeated watering. In early summer, pinch the shoot at 20 to 30 cm (8 to 12 in), tie new stems, and keep the soil moist without saturation. As soon as buds appear, fertilize moderately with more potassium. In summer, water deeply at the base during dry periods, harvest nearly open flowers, and continuously remove faded flower heads. Monitor for slugs, aphids, earwigs, spider mites, and gray mold. After the first frost, cut the stems, carefully lift the tuber, let its surface dry, label it Manhattan Island, and store it in a cool, dry, dark, and frost-free place. Check it monthly during winter. The deep red to yellow base contrast remains sharper when the plant receives at least six hours of direct sunlight and regular feeding without excess nitrogen. A stake installed early supports the 15.5 cm (6 in) flower heads after rain without compressing stems or damaging active roots. Remove faded flowers before seed formation so the plant directs its energy towards new buds until the first frost. Always water slowly at the base, then let the top layer breathe to maintain a balance between moisture, oxygen, and drainage. The deep red to yellow base hues combine particularly well with blue, white, purple perennials and light grasses.
Container growing
A garden,within reach.
Recommended pot size
Capacity 40 to 50 L, deep and very stable
Container gardening requires planning for the volume needed for the roots and the plant's final height. Choose a stable pot with drainage holes and a substrate suitable for planting. Leave enough space to respect the recommended depth and spacing, rather than crowding plants to immediately fill the pot. Place the container in the indicated exposure and regularly check for moisture, especially in hot or windy weather. A pot is more exposed to temperature variations than a plant in the ground. Therefore, plan from the outset for a wintering location compatible with the plant's needs and your region's climate. Plant in spring when all risk of frost has passed and the soil has sufficiently warmed. Choose a sunny spot, sheltered from strong winds, in fertile and well-drained soil. Arrange the tuberous roots with their crown and buds facing upwards, without breaking fragile attachments. Install a stake at planting if support will be necessary, to avoid damaging the roots later. Water sparingly at the start, then adjust watering to foliage growth. Consistently soggy soil around tubers should be avoided, especially before the first shoots appear. Plan to bring in storage organs indoors, away from frost, for the Quebec winter.
Bloom and dimensions
Its place,in your garden.
Mature height
110 cm (43 in)
Width / spread
20 in (50 cm)
Flower color
Deep red with a yellowish-green base
Foliage color
Green
Foliage type
Null and void
Growth rate
Quick
Bloom period
Spectacular flowering of large, decorative, bright red flowers with luminous yellow tips from July until the first frosts. The flowers are excellent for bouquets and attract pollinating insects. Giant Dahlia ‘Manhattan Island’ (Dahlia ‘Manhattan Island’) Giant Dahlia ‘Manhattan Island’ produces large decorative flowers where deep red dominates, illuminated by greenish-yellow at the base of the florets. This Dinnerplate variety creates a warm focal point in sunny beds, cutting gardens, and large containers. Harvest almost-open stems early in the morning, then continuously remove spent flowers to stimulate subsequent buds.
Harvest
July to October. Cut flowers early in the morning when fully open for excellent vase life. Continue to deadhead to prolong flowering.
Garden associations
In goodcompany.
Companion plants
To accompany Dahlia 'Manhattan Island', you could consider cosmos, zinnias, or ornamental salvias. Choose companion varieties based on their height, flowering period, and the colors you wish to combine. Most importantly, ensure that their sun exposure and water needs are suitable for the same location. Maintain enough distance so that the leaves do not shade young shoots and to allow easy access to each plant for maintenance. These associations are for composing the garden's decor; they do not guarantee protection against pests or diseases. Adjust the layout after observing one growing season.
Frequently asked questions
Your questions,answered.
When to plant the Manhattan Island dahlia?
Plant the tuber after the last frost, when the soil has warmed and is no longer saturated. Lay it 10 cm (4 in.) deep, bud facing up, in fertile, humus-rich, well-drained soil. Leave 50 cm (20 in.) around the crown and install a support immediately. In cold regions, start it in a pot four to six weeks earlier, then gradually acclimate the shoot before planting it out. Water very sparingly before emergence to prevent rot, then increase watering once the roots and stems are active. Full sun develops strong stems and intensifies the deep red and yellow contrast.
What colors do Manhattan Island flowers wear?
Manhattan Island produces greenish-yellow florets, broadly colored deep red towards the tips and edged with a fine red border. The proportion of red varies from petal to petal and flower head to flower head, creating a lively pattern rather than a perfectly regular band. The international register mentions flowers reaching approximately 15.5 cm (6 in), while Van Noort classifies the variety as Dinnerplate. Ample light helps the stems remain firm and makes the contrast sharper. However, avoid wetting the flowers when watering: water trapped between the petals can stain the colors and promote gray mold in cool weather.
How to support and make Manhattan Island flourish?
Install a sturdy stake at planting to avoid damaging the roots later. Tie the stems with soft ties as they grow. Pinch back the young shoot to 20-30 cm (8-12 inches) to encourage branching. Water deeply at the base when the surface dries, then allow excess water to drain. Incorporate mature compost initially and then use a moderate fertilizer, richer in potassium once buds form. Avoid excess nitrogen, which produces tender stems and a lot of foliage. Regularly remove faded flowers so that energy is directed to subsequent buds until frost.
Can Manhattan Island grow in a large pot?
Yes, choose a stable container of 40 to 50 L, deep, well-drained, and filled with rich yet aerated potting mix. Plant a single tuber 10 cm (4 in) deep and insert the support before the roots develop. Place the pot in full sun, protected from gusts. Water sparingly before sprouting, then abundantly when the top layer dries, without leaving water in the saucer. Apply a moderate liquid fertilizer, richer in potassium once buds appear. Rotate the container weekly, pinch back new growth, and remove faded flowers to maintain a balanced shape and generous blooms.
How do you winterize Manhattan Island in Quebec?
After the first frost that blackens the foliage, cut back the stems, leaving a short stub. Lift the tuber with a fork, working far enough away so as not to damage it. Gently remove excess soil, allow the surface to dry in a ventilated area, and clearly label it Manhattan Island. Store it in a cool, dry, dark, frost-free place, in a slightly insulating material that limits drying out without retaining water. Inspect it monthly. Remove only parts showing active rot and increase ventilation if condensation appears. Wait until the last spring frost and warm soil before replanting.
Wildlife and pets
Life,around your plants.
Supporting wildlife
The very double florets limit access to pollen and nectar. Manhattan Island contributes mainly through its ornamental value. To feed bees and butterflies, plant nearby sages, verbenas, coneflowers, or other single flowers rich in resources. The deep red contrast with a yellow base remains sharper when the plant receives at least six hours of direct sunlight and regular feeding without excess nitrogen.
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