This is the “Soul Man” of your garden. The hydrangea you purchased from your local nursery is probably a “Nikko Blue” or “Glory Blue” species. There are some 1200 different cultivars of hydrangeas. It belongs in the class Hydrangea macrophylla, in the “Mop Head” or “Hortense” sub-class. (i.e. not a lace cap.)
THIS PLANT / TEMPERATURES CENTRAL NORTH CAROLINA
This plant, in the picture, is less than a year old. You may keep it in a pot through the winter or you may plant one this fall. I would wait until the over 80 degree days are gone if you want to plant in the fall. It will survive the winter in the ground unless we get into single digit temperatures. If you keep it in a pot, you can probably plant it after February 15th as we may get some freezing days after that, but probably not into single digits.
Keep inside when temperatures are below 20 degrees or put a blanket on your “blues brother”. I have heard that many hydrangea including Nikko Blue require approximately 900 hours, or about 40 days with temperatures below 40 degrees in order to maintain their natural blooming cycle. These hours do not need to be consecutive. I leave my new plants outside all winter and only worry if the temperatures go into the low teens and single digits – a rare event in Central North Carolina.
Plant in good soil. I use a mixture of 2-3 parts commercial topsoil, 1 part dried manure, and 1 part peat moss. The hole should be at least twice as large as the pot. After planting add enough mixed soil to form a mound 2-3 inches above ground level. Soak well with a trickle drip or spray.
Locate where the plant will get the morning sun, but not the hot afternoon sun at least here in the south. Sometimes locating too close to large trees will cause problems in later years when the plant grows tall. (4′ to 6′). The roots of the tree will take so much water from the ground in the summer that mature hydrangea do not get enough water. You can also locate them in full shade but they may not reach full height for many years, if at all. Plant hydrangeas at least 4′ apart. If I am starting a new area, I plant them about 2’ apart with plans to remove half of them in about three years.
WATER / FERTILIZER
Hydrangea like water (hydra is a Greek word for water). The leaves will begin to droop if the soil is too dry. Some wilting in the late afternoon on hot summer days is fine – as long as the leaves spring back to normal overnight. Too much water and the leaves begin to get brown/black marks on the edges.
Use Miracle-Grow for Azeleas (used to be Miracle Acid to fertilize the plants. Follow the printed instructions – use approximately every two weeks in the growing season for maximum size. I have started using Osmocote as a slow release fertilizer with less risk of burning th plant. Two tablespoons under the canopy early in the season is plenty for a mature plant with perhaps a one tablespoon booster after blooming, mid to late summer depending on variety. For small plants use half that amount.
H. like an acidic soil – especially if you want the blue blooms. To supplement the fertilizer and add acid, you can use any of the following: aluminum sulfate (1/4 oz. per gal. of water), egg shells, coffee grounds, or ground up orange or grapefruit peels. If you want pink blooms, use less acidic fertilizer. Some lime lightly applied may be OK. Be careful to not make the soil too alkaline as that is not healthy for hydrangea.
STRESS / FUNGUS / INSECTS
If you detect black spotting or brown/gray coloration in the leaves, and you haven’t been watering regularly and/or the leaves have been drooping between watering, these may be signs of heat stress or fungus. Increase your watering.
Spotting or discoloration, if you have been regularly watering, may be a sign of a fungus. Fungus can come from over watering, watering too late in the afternoon (after 3:00 pm watering may cause fungus from the chemicals present in the local water supply) or from other sources. Try reducing your amount of water or watering earlier in the day. In either case, too dry or too wet, try using any all-purpose fungus treatment available in most garden shops. Follow directions and do not over treat. Fungus treatment will not repair damage done, but it should reduce future damage.
Similarly, if you find evidence of leaves being eaten, you may apply any all-purpose insecticide. Follow directions. Not all leaf damage is from fungus or insects. You may find isolated leaf damage from branches falling from above punching holes or some staining and holes from bird droppings. These are perfectly natural.
Another condition you may encounter is sun scalding. If you have a quick rain followed by a very hot sun, the remaining water can burn the petals and you will get smooth, almost round, brown spots. Not much you can do about this.
Buds start forming in late January and early February. They are not as tolerant of freezing temperatures. Late freezes after the buds start to form are a leading cause of no blooms later in the spring.
Blooms will start forming around the middle of April with the blooms out in early June. They will last until the end of June. Since these are first year plants, I recommend cutting just the blooms off as soon as they begin to grow more than an inch or so across. Do this through the end of next summer to let the plant mature with larger leaves and more stalks. The blooms are pretty, but will cause the plant to not grow as much. If you want them to come in to a full color, enjoy the blooms for a couple of days, but prune them soon to improve the long term health of the plant.
On a mature plant, the blooms will last some 4-6 weeks. They start almost white and then turn pink or blue depending on the soil. Some plants and even some blooms may have both pink and blue on them. As the blooms mature, they turn to a more purple/lavender color, then to lime green, and finally white & brown. Let them stay on the plant or cut them off. I cut them when they turn green as this seems to spur growth on the nearby stalks. Some cut them for drying.
STEMS / PRUNING
Do NOT cut the brown stems off in the winter. The brown stems are what next year’s blooms will grow on. You may top them for shaping the plant by taking off an inch or so on smaller plants and three to five inches on larger plants. Cut just above a node (joint). They seem to like this “haircut.” The next winter the brown stems will turn a whiter color and eventually will separate from the root. You can pull gently on the whiter colored stems. If they come off in your hand, fine, if not, leave them for a couple of months and try again.
On a very full mature plant, you can remove some of the brown stems completely to encourage less, but larger blooms the next year. Leave the stems alone for more, smaller blooms.
After the first full year, you may choose the level of care you wish to give hydrangea. Except for watering, they require very little care for good results. Or, you can prune, fertilize, and treat for fungus and leaf eating bugs if these conditions appear for exceptional results.
With a lot of care I have had cobalt blue and brilliant pink mop heads as big at 10 inches across and leaves as long as 12 inches and as wide as 9 inches. The plant will grow from 4′ to 6′ tall with good soil, watering, feeding, and morning sun location.