Plant hydrangeas (Hydrangea spp.) in the right place to help them thrive and produce an abundance of flowers year after year. Putting the shrubs in an area that does not provide the correct amount of sunlight will cause them to struggle to survive or fail to bloom. Timing can make a difference, too. Avoid planting hydrangeas during hot, dry weather.
Select hydrangeas that are hardy in your U.S. Department of Agriculture plant hardiness zone. If, for example, you live in an area that has cold winters, then go with panicle hydrangea (Hydrangea paniculata). It and some of its cultivars are hardy in USDA zones 3 through 8, although the cultivar 'Limelight' (Hydrangea paniculata 'Limelight') is hardy in USDA zones 4 through 8.
If you are in a location with hot summers, then grow bigleaf hydrangea (Hydrangea macrophylla, USDA zones 5 through 9), oakleaf hydrangea (Hydrangea quercifolia, USDA zones 5 through 9) or Golden Crane hydrangea (Hydrangea angustipetala 'MonLongShou' or Hydrangea scandens subsp. chinensis 'MonLongShou,' USDA zones 6 through 10). Other options for a hot-summer area include 'Mini Penny' (Hydrangea macrophylla 'Mini Penny,' USDA zones 4 through 9) and smooth hydrangea (Hydrangea arborescens, USDA zones 3 through 9).
Deciding When to Plant
If you are in a northern U.S. region that has cold winters, then plant hydrangeas in late summer to very early fall, or plant them in early summer or spring after your location's last average frost date. Plant them in winter after the danger of freezing temperatures has passed if you are in a mild-winter southern area where temperatures rarely fall below freezing.
Selecting Where to Plant
The best place to plant hydrangeas offers direct morning sunlight and afternoon shade. Hydrangeas in shadier positions bloom less than normal or not at all. In a cool, northern area, Peegee hydrangea (Hydrangea paniculata 'Grandiflora,' USDA zones 3 through 8) can be planted in full sun as long as it is watered once or twice each week during summer.
Plant hydrangeas where they can become their full sizes with a few inches to spare, or plant them 3 to 10 feet apart. A hydrangea's size depends on its variety. Most hydrangeas grow to a height and width of 3 to 6 feet, but panicle hydrangea can reach 20 feet tall and wide. Peegee can grow 10 feet tall and wide.
Preparing the Soil
Hydrangeas grow best in soil that drains quickly and contains organic matter. Mix a 2- to 3-inch layer of well-aged manure, compost, leaf mold, sphagnum peat moss or composted shredded pine bark mulch with the soil to a depth of 1 foot before planting.
The soil's pH, or acidity, level is not especially important unless you plant bigleaf hydrangea, or serrated or mountain hydrangea (Hydrangea serrata, USDA zones 6 through 9) and you want either blue or pink flowers. Soil with a pH level of 6 to 6.2 turns their flowers pink while 5.2 to 5.5 pH turns them blue. Add sulfur to the soil to lower the pH or lime to raise it. Test the soil with a soil test kit first, though, to determine its current pH level and how much of an adjustment is necessary; test the soil after you added compost or a different organic amendment when you prepared the soil because the amendment can change the pH level.
Planting the Hydrangeas
Remove each hydrangea from its plant nursery container, keeping the soil on top of each root ball. Determine the proper planting depth for each shrub by measuring from the top of the soil above the plant's root ball to the root ball's bottom. Slide the hydrangeas back into their containers, and keep them in the shade. Do not let their roots dry out.
Dig a planting hole, making its depth equal to the root ball and soil measurement of one hydrangea if the soil drains fast or 10 percent less than that measurement if the soil drains more slowly. Do not loosen the soil at the bottom of the hole. When the hydrangea is in the hole, the top of the container soil still covering its root ball should be even with or slightly higher than the surrounding soil. The planting hole should be 1 1/2 to three times the width of the root ball. Use the same procedure to make each hydrangea's planting hole.
Sterilize pruners with a household disinfectant, and rinse it with clean water. Remove one hydrangea from its container, and use the sterilized pruners to cut all roots encircling the outside of the root ball. Cut those roots at their top, near the base of the shrub. Repeat the process for each hydrangea, sterilizing the pruners for each one.
Set a hydrangea in its planting hole without the soil from its nursery container. Fill the bottom one-half of the hole with the soil you removed when digging the hole. Pour 1 gallon of water into the hole, settling the soil. Finish filling the hole with soil. Do not place soil on top of the root ball. Plant each hydrangea by using the same method.
Construct a 2- to 3-inch-high soil ring around each hydrangea just at the edge of its planting hole so that water will be forced to soak in right above the root ball. Water each hydrangea with 1 gallon of water.
Spread a 2- to 3-inch depth of organic mulch on the soil around each hydrangea, but spread it to only 1/2 to 1 inch deep on top of the root ball. Keep the mulch 2 to 3 inches from the stems to prevent fungal and bacterial diseases.
Water the newly planted hydrangeas often enough to keep their root balls moist. Check the root balls' moisture level by poking your finger into each one's middle. If a root ball's soil feels wet, it does not need to be watered. If it is beginning to get dry, pour 1 gallon of water slowly over the root ball.