How to Grow Longwood Blue
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Longwood Blue
Hydrangea macrophylla 'Longwood Blue'
shrubLongwood Blue is a deciduous bigleaf hydrangea cultivar known for its vibrant blue mophead flowers that bloom prolifically throughout the season. This compact to medium-sized shrub produces large, lacey flower clusters and attractive dark green foliage. It's a heat-tolerant variety that reblooms reliably even in warmer climates.
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Example Longwood Blue timeline · Pittsburgh, PA (Zone 6b)
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Plant Longwood Blue
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Longwood Blue
Late summer into fallBefore the first fall frost (≈ Nov 8)
Sample dates for Pittsburgh, PA. Sign up to get exact Longwood Blue dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 5-9, with excellent performance in zones 6-8
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Get my Longwood Blue timeline →Growth Stages
Establishment
Year 1Young shrub with basic branching structure and limited flowering in first year; focus on root development and foliage establishment
Water consistently, avoid fertilizing heavily first year, prune lightly to shape. Mulch well to retain moisture.
Vegetative Growth
Spring-early summerPlant develops fuller branching architecture with larger leaves; increased shoot production throughout growing season
Pinch back stems in early summer to encourage branching. Apply balanced fertilizer monthly during growing season. Continue consistent watering.
Bud Formation
Mid-summerFlower buds develop on new growth; visible bud clusters appear at branch tips
Reduce nitrogen to promote flowering; apply phosphorus-rich fertilizer. Maintain consistent moisture and afternoon shade. Stop pinching back by mid-July.
Flowering
July-October (can rebloom if deadheaded)Large mophead flower clusters (lacecaps possible on older wood) bloom in vibrant blue, often with continuous reblooming if spent flowers removed
Deadhead spent flowers to encourage rebloom. Continue watering deeply during hot periods. Protect from intense afternoon sun in hot regions. Support heavy flower clusters if needed.
Dormancy
November-MarchFoliage turns reddish-bronze before dropping; plant enters winter rest period with woody canes remaining
Stop fertilizing after August. Allow plant to harden off naturally. Prune only dead wood in late winter/early spring before new growth emerges.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Spray with horticultural oil in early spring before buds break; treat crawlers with insecticidal soap in summer. Remove heavily infested branches.
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Improve air circulation by pruning, avoid overhead watering, apply sulfur fungicide in early stages, water at soil level only
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Hand-pick in early morning, use pheromone traps away from plant, apply neem oil or insecticidal soap, encourage natural predators
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Increase humidity with regular misting, spray with strong water jet, apply miticide if severe, ensure adequate moisture
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Remove affected leaves, improve air circulation, avoid wetting foliage, apply fungicide if widespread
Uses
Landscape Specimen
OrnamentalLongwood Blue serves as a stunning focal point in partial shade gardens and mixed borders with its profuse blue blooms and attractive summer foliage. Its compact habit makes it ideal for smaller gardens and containers. [source]
Cut Flowers & Dried Arrangements
CraftThe large, full flower heads are excellent for fresh floral arrangements and dry beautifully for lasting decorative displays. Flowers transition to dusty rose and burgundy tones as they age, adding visual interest. [source]
Pollinator Support
WildlifeThe abundant flowers provide nectar and pollen for bees, butterflies, and other pollinators throughout the summer and into fall. The mophead form offers easy access for insects. [source]
Garden Color & Screen
HouseholdCreates a colorful seasonal screen or privacy barrier and adds vibrant blue tones to shade gardens where many other flowering plants struggle. Matures to 3-5 feet tall and wide. [source]
Harvest Tips
This is a flowering ornamental shrub, not grown for harvest. Deadhead spent flower clusters to promote continuous reblooming throughout the season. Cut faded flowers just below the cluster. For cut flowers, harvest in early morning when stems are well-hydrated; select clusters showing some color development for longest vase life (5-10 days).
Fun Facts
- 🌱 The blue color in bigleaf hydrangeas depends on soil pH and aluminum availability—the same genetic variety can produce blue flowers in acidic soil and pink flowers in alkaline soil. 'Longwood Blue' was specifically bred to maintain blue coloring across a wider pH range than older varieties.
- 🌱 Longwood Blue is a reblooming cultivar developed at Longwood Gardens in Pennsylvania, meaning it produces flowers on new growth throughout the season rather than only on old wood, making it more reliable for late summer blooms.
- 🌱 Unlike most bigleaf hydrangeas that only flower on previous year's wood, this cultivar's habit of blooming on new growth means even if winter freezes kill flower buds, the plant will still flower later in the season from new shoots.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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