Hydrangea shrubs are categorized into six main species. Hydrangeas are differentiated by flower type, size, growing habits, and cold hardiness. When buying your hydrangea make sure you understand the type you are getting and the growing requirements needed.
Hydrangeas are great plants for producing copious amounts of flowers over the summer into early fall. They all have different pruning needs. Old wood plants also put all their energy into bud production at once after flowering, so they look bedraggled in the garden, often developing spots on their leaves. Treating them can cause more harm than good.
Hydrangea Macrophylla
Hydrangea macrophylla, which referred to as mophead or Lace cap, blooms on old wood. Once they have finished flowering in late summer, they begin to use their energy to develop flower buds for the next season. Once you prune, remaining leaves will not look pretty as all energy goes into producing next year’s buds. If you wait too long you must decide between a flower bud and a leaf bud. Prune to the top of the flower bud which is the larger of the buds. Prune so flower buds are all at the terminal end of the stem. The flower bud is two to three times larger than a leaf bud. You follow each stem down to the flower bud and make your cut. Never straight shear a Hydrangea macrophylla making it even instead cut to a bud, remove crossing limbs, remove dying or dead limbs, and tidy its shape if needed. Early spring freezes can harm their buds.
Hydrangea macrophylla Mophead
Hydrangea macrophylla lace cap
Hydrangea Serrata
Hydrangea serrata (Mountain Hydrangea) is smaller than Hydrangea macrophylla and cold tolerant. The leaves turn a deep maroon in fall and if placed properly they need little pruning. They come in lace cap and mophead flowers. Most are dwarfs, growing to less than 3 feet tall and wide. Serrata’s are cold hardy, bloom on old wood and due to size require very little pruning. Old flowers can be tipped off and any damaged stems can be removed after flowering.
Hydrangea serrata lace cap
Hydrangea serrata mophead
Hydrangeas That Bloom on New Wood
The next two species bloom on new wood. Hydrangea aborescens (Smooth Hydrangea), native to the eastern US grows in full to part sun with adequate moisture. Hydrangea paniculata (Paniculated Hydrangea) prefers more sun than other hydrangeas. Blooming on new wood means as they grow in the spring, they develop all new buds on their stems. Prune in late winter or early spring once the coldest weather has passed. By leaving the stems on over the winter you protect the crown of the plant from freezing and heaving. Pruned to eighteen to twenty-four inches in height and width. Remove any dead or unhealthy branches to the ground. Crossing branches should also be eliminated. Harsh spring weather will not interfere with their flowering.
Hydrangea arborescens
Hydrangea paniculata
Remontant Hydrangeas (Bloom on Old and New Wood)
There are remontant hydrangeas like the Endless Summer Series (Hydrangea macrophylla), Let’s Dance Series (Hydrangea macrophylla), and Tuff Stuff series (Hydrangea serrata). These produce on both old and new wood. They are mophead and lace cap flowering depending on variety. Plant where they have all the room they need to reach their potential. Pruning will remove buds whenever you choose to do it. Sizes range from 3-4 feet to larger ones growing to six feet or taller. If you live in a cooler climate the Tuff Stuff series, commonly called Mountain Hydrangea, develops a lace cap flower and is the least likely to burn in winter. New varieties are coming on the market with color variations from lavender to fuchsia.
Endless Summer
Tuff Stuff
Hydrangea Quercifolia (Oakleaf Hydrangea)
Hydrangea quercifolia or oakleaf is native to the southeastern US and prefers morning sun in hotter areas to full sun in cooler climates. They are found growing on banks, along wood’s edge, and along streams. They prefer a loamy moist soil. They develop large panicles of creamy flower that fade to marroon to brown. The leaves offer nice fall colors of orange to maroon. The species can grow to 8 feet tall and wide. There are many cultivars that stay smaller like Ruby Slippers, Sikes Dwarf, Pee Wee and Munchkin whch all grow to 3-4 feet tall and wide. This is a great plant which is frequented by many native pollinators and birds.
Hydrangea quercifolia summer
Hydrangea quercifolia fall color
Hydrangea Growing Tips
Hydrangeas are easy to grow as long as they are planted in the proper location – know which one you are buying. Most Mopheads with their large green leaves prefer afternoon shade and in hot humid areas dappled or all day shade. All hydrangea wilt during the heat of the day to limit transpiration of water from their leaves. If the leaves unfurl at night it does not mean they need to be watered – check your soil first. The equivalent of a inch of rain weekly is sufficient to maintain hydrangeas except in the hottest weather then twice weekly applications of water may be needed. It is best no to wet the leaves when applying water.
The soil pH indicates the color of your hydrangea blooms – white will always be white – Hydrangea macrophylla or big leaf and Hydrangea serrata or mountain are the only ones that can be changed by adjusting soil pH. To maintain a blue color the pH should be 5.5 or slightly lower. Add aluminum sulfate around the drip line beginning in the late winter to change the color of your hydrangea. Sometimes it may take a full year to see coloration changes depending on the quality of the soil. You can purchase a pH meter to monitor the pH. Having too much phosphorous in your soil and leaching lime from foundations and sidewalks can also inhibit the uptake of aluminum sulfate.
Spraying hydrangeas for fungal issues in late summer and fall is not a good practice as they are feeding their roots and buds for net season Sprays can interfere with photosynthesis by putting a sheen on the leaves. By the time most homeowners notice discoloration of leaves or spots the damage is done. Proper placement, proper watering, and planting the correct variety are important when choosing a hydrangea.
Photo Credits: Great Garden Plants, Proven Winners, Garden Goodies, Maryland Extension, Gardenia
