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Tuber
Asteraceae
Giant Dahlia 'Penhill Watermelon' (Dahlia)
Dahlia × pinnata
Penhill Watermelon produces large, double coral-pink to pale-mauve flowers on an upright clump reaching 150 cm (59 in). The No1 Van Noort tuber should be planted 10 cm (4 in) deep, in full sun, in fertile, humus-rich, well-drained soil. Install robust support early, pinch the shoot, water deeply at the base, and remove spent flowers until frost. This Dinnerplate variety is suitable for beds, large pots, and bouquets. In Quebec, lift the tuber in autumn and store it in a cool, dry, frost-free place. Its wavy petals create remarkable movement in all light conditions. Flowering renews from mid-summer until the first frosts.
- Quantity
- 1 tuber
- Exposure
- Sun
- Life cycle
- Tender perennial
- Hardiness
- Zone 8
Discover the plant
Common nameGiant Dahlia ‘Penhill Watermelon’
FamilyAsteraceae
GenusDahlia
TypeTuber
Botanical nameDahlia × pinnata
‘Penhill Watermelon’ Giant Dahlia (Dahlia). ‘Penhill Watermelon’ Giant Dahlia (Dahlia) The ‘Penhill Watermelon’ giant dahlia features large, double flowers with petals that transition from coral pink to pale mauve. Broad, wavy, and twisted, the florets curve in multiple directions, giving the flower head a fluid, almost aquatic movement. The dark green foliage, tinged with bronze, provides a rich contrast. Van Noort’s No. 1 tuber produces an upright clump that can reach approximately 150 cm (59 in.) in height and 50 cm (20 in.) in spread. From mid-summer until the first frost, flowers continuously bloom on stems useful for beds, cutting gardens, and large containers.
Their nuanced palette changes with the light, creating a romantic focal point without appearing uniform. Plant ‘Penhill Watermelon’ in spring after the last frost, when the soil is warm. Lay the tuber 10 cm (4 in.) deep, bud facing upwards, in fertile, humus-rich, moist, and well-drained soil. Leave 50 cm (20 in.) around the crown, choose full sun, and protect the plant from strong winds. Install sturdy support at planting, as the clump can reach 150 cm (59 in.) and the large flowers retain rain. Water sparingly before emergence, then deeply at the base when the surface dries.
Pinch back young shoots at 20 to 30 cm (8 to 12 in.) to encourage branching. Well-rotted compost and moderate fertilization, richer in potassium at the bud stage, support firm stems without excess nitrogen. Pair ‘Penhill Watermelon’ with violet-blue salvias, white gauras, chocolate cosmos, and coppery grasses. These companions highlight the coral pink and pale mauve tones while allowing the wavy petals to breathe. Harvest almost open stems early in the morning, then continuously remove spent flowers. The very double flower heads offer few accessible resources for pollinators; therefore, add simple flowers nearby. For a larger flower, keep the terminal bud and remove the lateral buds.
Planting guide
Plant well.Grow beautifully.
Planting depth
10 cm (4 in)
Best planting time
Spring, when the ground is warm
Propagation
Division of tubers, each bearing a viable bud
Growing method
After the last frost, loosen a sunny area to 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 water only 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 buds. Tie the stems with soft ties, harvest flowers when almost open, and remove faded 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 coral pink to pale mauve contrast 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 7-inch (18 cm) flower heads after rain without compressing stems or damaging active roots. Remove faded flowers before seed formation so 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 limits evaporation and helps maintain constant moisture during the summer. Water sparingly before emergence, then deeply at the base when the surface dries out. In Quebec, after the first frost, 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 exit the root zone. Work the soil when it is dry enough 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 water accumulation 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. Follow the recommended dosage and then water. Too much nitrogen produces tender stems and fewer flowers. The coral pink to pale mauve 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 sprouting, avoid repeated watering. In early summer, pinch the shoot back to 20 or 30 cm (8 to 12 in), tie new stems, and keep the soil moist without saturation. Once buds appear, fertilize moderately with more potassium. In summer, water deeply at the base during dry periods, harvest flowers when almost open, and continuously remove faded flower heads. Watch for slugs, aphids, earwigs, spider mites, and gray mold. After the first frost, cut back stems, gently lift the tuber, let its surface dry, label it Penhill Watermelon, and store it in the dark, in a cool, dry, and frost-free place. Check it monthly during winter. The coral pink to pale mauve contrast 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 18 cm (7 in) flower heads after rain without compressing stems or damaging active roots. Remove faded flowers before seed formation so the clump directs its energy towards new buds until the first frost. Always water slowly at the base, then allow the top layer to breathe to maintain a balance of moisture, oxygen, and drainage. The coral pink to pale mauve hues pair particularly well with blue, white, and purple perennials, and light grasses.
Container growing
A garden,within reach.
Recommended pot size
Capacity of 40 to 50 L, deep and very stable
Container gardening requires considering the volume needed for the roots and the final height of the plant. 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 the moisture level, especially in hot or windy weather. A pot is more exposed to temperature variations than a plant in the ground. Therefore, plan for a wintering location compatible with the plant's needs and your region's climate from the outset. Plant in the spring when all risk of frost has passed and the soil is sufficiently warmed. Choose a sunny location, sheltered from strong winds, in fertile and well-drained soil. Arrange the tuberous roots with their crown and buds facing upwards, without breaking the fragile attachments. Install a stake at planting if support will be necessary, to avoid injuring the roots later. Water sparingly at the start, then adapt the watering to the foliage growth. Constantly soggy soil around the tubers should be avoided, especially before the first shoots appear. Plan to bring storage organs indoors, away from frost, for the Quebec winter.
Bloom and dimensions
Its place,in your garden.
Mature height
120 cm (48 in)
Width / spread
50 cm (20 in)
Flower color
Coral rose to pale mauve
Foliage color
Green
Foliage type
Null and void
Growth rate
Quick
Bloom period
Spectacular blooms of very large decorative watermelon pink flowers from July until the first frosts. Giant Dahlia 'Penhill Watermelon' (Dahlia 'Penhill Watermelon') The giant dahlia 'Penhill Watermelon' unfurls large double flowers with petals that range from coral pink to pale mauve. From mid-summer until the first frost, the flowers continuously bloom on stems that are useful for beds, cutting gardens, and large containers. Install a sturdy support at the time of planting, as the clump can reach 150 cm (59 in) and the large flowers retain rain.
Harvest
July to October. Harvest the flowers early in the morning when fully open to ensure excellent vase life. Continue to deadhead spent blooms to encourage the production of new buds.
Garden associations
In goodcompany.
Companion plants
Salvias, cosmos, Verbena bonariensis, echinaceas, and ornamental grasses beautifully highlight its large, softly colored flowers. The dark green, bronze-tinged foliage creates a rich contrast. Their nuanced palette changes with the light, creating a romantic focal point without appearing uniform. Pair 'Penhill Watermelon' with purplish-blue salvias, white gaura, chocolate cosmos, and coppery grasses. These companions emphasize the coral-pink and pale mauve tones while allowing the wavy petals to breathe.
Frequently asked questions
Your questions,answered.
When to plant Dahlia Penhill Watermelon?
Plant the tuber after the last frost, when the soil has warmed up and is no longer waterlogged. Lay it 10 cm (4 in.) deep, bud facing upwards, in fertile, humus-rich, well-drained soil. Leave 50 cm (20 in.) around the crown and install a support immediately. In a cold region, start it in a pot four to six weeks earlier, then gradually acclimatize the shoot before transplanting. Water very little before emergence to prevent rot, then increase watering once the roots and stems are active. Full sun develops strong stems and intensifies the coral pink to pale purple contrast.
What colors are the Penhill Watermelon flowers?
Penhill Watermelon produces pale lilac florets, broadly colored with coral pink towards the tip and edged with a thin red line. The proportion of red varies from petal to petal and from head to head, creating a lively pattern rather than a perfectly regular band. The international register mentions flowers reaching about 18 cm (7 in), while Van Noort classifies the variety as a Dinnerplate. Abundant light helps the stems remain firm and makes the contrast sharper. However, avoid wetting the flowers when watering: water trapped between the petals can mark the colors and encourage gray mold in cool weather.
How to support and help Penhill Watermelon thrive?
Install a sturdy stake at planting to avoid damaging the roots later. Tie the stems with soft ties as they grow. Pinch back young shoots to 20-30 cm (8-12 in.) to encourage branching. Water deeply at the base when the surface is dry, then allow excess water to drain. Incorporate mature compost initially, 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 spent flowers so that energy is directed to subsequent buds until frost.
Can Penhill Watermelon grow in a large pot?
Yes, choose a stable container of 40 to 50 L, deep, well-drained, and filled with rich but aerated potting soil. Plant a single tuber 10 cm (4 inches) 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 moderate liquid fertilization, richer in potassium as soon as buds appear. Turn the container weekly, pinch back new growth, and remove faded flowers to maintain a balanced shape and generous blooms.
How to overwinter Penhill Watermelon 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 not to damage it. Gently remove excess soil, allow the surface to dry in a ventilated area, and clearly label it Penhill Watermelon. Store it in a cool, dark, dry, and frost-free place, in a slightly insulating material that limits desiccation without retaining water. Inspect it monthly. Remove only the parts showing active rot and increase ventilation if condensation appears. Wait for the last spring frost and warmed soil before replanting.
Wildlife and pets
Life,around your plants.
Supporting wildlife
The very double florets limit access to pollen and nectar. Penhill Watermelon contributes primarily to ornamental value. To feed bees and butterflies, plant salvias, verbenas, echinaceas, or other simple flowers rich in resources nearby. The coral pink to pale mauve contrast remains sharper when the plant receives at least six hours of direct sunlight and regular feeding without excess nitrogen.
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