Growing Hydrangea Tree Form

Latin Name Pronunciation: hye-dran' jee-uh  

From Eastern Asia, Hydrangea paniculata is likely the easiest, most adaptable and hardiest Hydrangea of all. Unfussy about soil as long as it is well-drained, they’re at their best in full sun; provide afternoon shade in warmer climates. Flower buds form in spring, blooming on the current growing season’s stems (new wood).

On arrival: Your bareroot Hydrangea tree has been stored in a temperature-controlled cooler, which simulates winter and keeps the plant dormant. A dormant plant is unaffected by cold weather and can be planted as soon as you are able to dig a hole in the ground. If you cannot plant immediately, your tree may be stored upright in its wrapping material in a cool, dark place such as a basement, garage, or unheated shed, for a week or so. Keep it away from direct sun.

Planting a bareroot tree: Select a spot in your garden that is sheltered from strong winds. When you’re ready to plant, unwrap your tree and remove the packing material.

• Soak the roots of your tree in a container of water for a couple hours to rehydrate them.
• Dig a hole wider than the spread of the roots and deep enough to accommodate them, allowing for adjustments.
• Use excavated soil to form a mound in the center of the hole.
• Set the tree on top of the mound, fanning its roots outward. Adjust the height of the mound by adding or removing soil until the tree is positioned so that the crown (where the roots meet the stem) is at the surrounding soil level. Roots should all be below grade when the hole is filled.
• Check from all sides to make sure that the trunk is perfectly upright, not leaning in any direction.
• Backfill the hole with soil about halfway and water well, allowing water to soak in and settle the soil. Re-check for upright trunk alignment. Then add remaining soil to the top of the hole, creating a little dam around the outer edge, and water again.
• It is best to stake a young tree for extra support until its trunk attains sturdy proportions. Choose a stake that has a diameter at least as large as the stem’s diameter and long enough that when pushed firmly into the soil, it reaches inside the head of the tree. Fasten the trunk to the stake at several points with garden twine or soft ties. Check the ties periodically and loosen them if they constrict the outward growth of the stem.

Establishing a bareroot tree: Do not fertilize when planting or for the first growing season.

• Because a bareroot plant is dormant, it cannot take up much water. Refrain from watering after the initial planting until the tree leafs out and begins actively growing, unless you are experiencing extreme drought conditions.
• Minimal pruning is needed until one or two growing seasons have passed, although any suckers or growth that sprouts from the trunk should be promptly removed.
• Once the plant has broken dormancy, care for as described in the Growing Guide for all Hydrangea paniculata varieties.

Growing your Tree Hydrangea in a Container

With some extra work and heavy lifting, it is possible to grow a Hydrangea tree or shrub in a container, but this is generally not a long-term proposition. Choose a sturdy container with drainage holes that is large enough to accommodate the fanned-out roots with about 3" all around to spare (for insulation) The container should be 24-28" wide and deep. To protect a costly or fragile ornamental container and make removal easier, you may want to plant in a plastic pot that fits inside a slightly larger decorative pot.

Planting, Watering, and Fertilizing: Mix together equal amounts of high-quality potting mix and compost sufficient to fill your container. Moisten the mix and plant according to the directions above for planting and establishing a bareroot tree.

Once your Hydrangea tree is actively growing, it will need more water than if planted in the ground. Soak deeply when soil feels dry to the touch an inch down, usually at least once a week. More frequent watering will be needed in hot weather and as flower buds are forming. Because frequent watering leaches nutrients from the soil, fertilize with a balanced liquid or water-soluble fertilizer according to directions on the label.

Repotting: Although a container-grown tree’s root growth will be restricted to a degree, at some point, it will outgrow the pot or simply need to have its soil refreshed, as the potting mixture degrades over time. If the soil level sinks, begins to dry out more quickly than previously, or if leaves frequently wilt, repotting is in order, usually every 2-3 years. Repotting is best done in spring. Loosen the bond between the soil and the pot by running a knife along the inside surface of the pot and ease the tree out.

If you wish to keep your plant in the same container, some of the roots will need to be pruned and an inch or two of the soil on the outside of the root ball removed. Gently shake out some of the old soil and replant, adding new compost/potting soil mix as needed. To move your plant into to a larger container, choose a pot that is 3-4" larger in all dimensions. Make a few slices into the soil of the root ball to untangle roots and encourage outward growth. After repotting, water deeply and set in the shade to recover for a few days.

Wintering Over in Containers: In colder climates (Zones 4-6), you can overwinter Hydrangeas by moving them to an unheated garage or shed, where temperatures range between 25-40°F. Check the potting mix occasionally for moisture and water as needed. In warmer climates where freeze-thaw cycles occur, store plants on a protected porch away from direct sun. Plants can remain outdoors in containers and enjoyed year-round where freezing is not a concern.

Pruning a Tree form Hydrangea paniculata

At first, prune lightly in late winter or early spring to encourage a good shape as form is being established. After a year or two, a harder pruning that removes up to half of the top growth will encourage sturdy branching.