Southern Ag Aluminum Sulfate (5 lb)
Soil pH below 5.5 turns mophead blooms blue; above 7 they go pink. A 5-lb bag dug lightly around the drip line shifts color in a single season.

Hydrangeaceae
Hydrangea macrophylla
Mophead blooms that anchor a garden bed with quiet drama
Basile Morin via Wikimedia Commons (cc by_sa_4)
About this plant
Hydrangea macrophylla is the classic flowering shrub that has anchored cottage gardens and suburban borders for generations. It belongs to the Hydrangeaceae family and grows as a perennial, meaning it comes back year after year once it is established outdoors. For a beginner-rated plant, it delivers a remarkable amount of presence, those large, rounded flower clusters are the reason gardeners keep coming back to this genus.
What makes this hydrangea especially appealing for first-time growers is its forgiving nature. It asks for only about ten minutes of care per week and has medium water needs, which means it sits comfortably between a drought-tolerant succulent and a thirsty tropical. Its USDA hardiness range spans an extraordinary breadth, Zones 1a through 13b, making it one of the most widely adaptable perennials you can plant in the ground across the United States. Whether you are gardening in a cold northern climate or a warm southern one, Hydrangea macrophylla is worth a serious look.
The gallery

Bloom
Raul654 via Wikimedia Commons (cc by_sa_3)

Gallery
Didier Descouens via Wikimedia Commons (cc by_sa_4)

Gallery
Alvesgaspar via Wikimedia Commons (cc by_sa_3)
How to grow it
Written for beginners. If you've never grown anything before, this is all you need to keep this plant alive and happy.
Find a spot with enough light for its needs. Plant it outdoors, ideally sheltered from the harshest afternoon wind.
Any good all-purpose potting mix or well-drained garden soil will do. Give each plant enough room for its mature spread. Crowding causes more problems than undersizing the bed. Water it in gently once it's settled.
Water when the top inch of soil feels dry, roughly once a week in summer. Soak the soil, then let it breathe before the next round.
This one is very forgiving. A balanced all-purpose fertiliser at the start of the growing season is plenty, and you can skip a month without harm. Plan on 10 minutes a week of hands-on care: watering, a quick trim, checking for pests.
Watch for new growth in spring and summer. If the leaves look tired, trim the oldest ones back to encourage fresh foliage.
Year at a glance
Approximate for a temperate North American zone. Shift earlier the further south you garden, later the further north.
Jan
January: Rest
Dormant
Feb
February: Rest
Dormant
Mar
March: Wake up
New growth
Apr
April: Tend
Routine care
May
May: Tend
Routine care
Jun
June: Tend
Routine care
Jul
July: Tend
Routine care
Aug
August: Tend
Routine care
Sep
September: Tend
Routine care
Oct
October: Tend
Routine care
Nov
November: Wind down
Prep for dormancy
Dec
December: Rest
Dormant
Pet & people safety
The card below lists the species affected and the specific symptoms reported by the ASPCA or Pet Poison Helpline. Place it out of reach, and call the poison-control number if a pet or child has eaten any part of it.
Dogs
Toxic
Symptoms. Vomiting, diarrhea, depression, lethargy after chewing leaves or flower buds.
Contains cyanogenic glycosides (amygdalin). Large ingestions needed for serious effects, but all parts are unsafe.
Source: ASPCA
Record covers Bigleaf Hydrangea toxicity for Dogs.
Cats
Toxic
Symptoms. GI upset, vomiting, diarrhea, depression.
Cyanogenic glycoside mechanism. Keep out of reach.
Source: ASPCA
Record covers Bigleaf Hydrangea toxicity for Cats.
Bloomwise is not a substitute for veterinary or medical advice. Every line above comes from a hand-verified reference.
Recommended supplies
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Frequently asked
Sources
Plant facts on this page come from a blend of public-domain and open-licensed datasets: Biodiversity Heritage Library (historical botanical illustrations, public domain), USDA PLANTS (taxonomy, public domain), GBIF (occurrence and taxonomy, CC-BY 4.0), OpenFarm (crop guides, CC-BY-SA 3.0), and Open-Meteo (climate and hardiness lookup, CC-BY 4.0). Toxicity records come from the ASPCA Animal Poison Control Center and the Pet Poison Helpline; every row is hand-verified against a primary reference.