All About Hydrangeas

Hydrangeas are medium sized deciduous shrubs with large leaves and attractive, long-lasting summer flowers. The large showy flowers appear in midsummer to late summer and vary in form from flat “Lacecap” clusters, to big globe shaped flowers to tall upright panicles. Flower color on the blue varieties will vary from pink to blue depending on how acidic the soil is. Hydrangeas prefer sun to partial shade and moist, well drained soil.

Arborescens (Smooth) Hydrangea

This New England native boasts large clusters of 4-6” dull white to pink flowers from June into later summer. These shrubs are hardy to zone 4 and prefer sun to partial shade. Most have a mounding habit and will grow 3 to 5 feet tall and 4 to 6 feet wide. Varieties include: Annabelle (white flowers) and Invincible Spirit (pink flowers).

Macrophylla Hydrangea

(Big Leaf & Lacecap)

This rounded, deciduous shrub will quickly grow between 3 and 6 feet tall and just as wide. Numerous cultivars make a flower description difficult; however, they are all magnificent. Flower colors range from white and pink to purple and blue.

Most varieties bloom from July through August, some lasting longer. For the Big Leaf Hydrangeas, flower color depends on the soil pH; acid soil procedures blue flowers, alkaline produces pink. Of the listed varieties below, these seem to be the hardiest and the most consistent flowering of the Macrophyllas for our area.

Varieties include: Endless Summer, Twist & Shout, Blushing Bride, and Big Daddy, Glowing Embers, and Nikko Blue.

Paniculata (Panicle) Hydrangea

Hardy to zone 4, this hydrangea’s branching resembles a fountain; branches come from one central point and cascade over. A taller variety, these can reach heights of 6 to 10 feet. Panicle hydrangeas can also come in a tree form. White flowers emerge in mid July and mature to pinkish hue by September. Flowers are very fragrant and great for cutting and drying.

Varieties include: Pee Gee, Kyushu, Limelight, Pink Diamond, and Tardiva.

Quercifolia (Oakleaf) Hydrangea

These plants are wider than they are tall and can get as tall as 8 feet, but most do not exceed 4 to 6 feet. The oak-like leaf shape is a dark green color throughout the summer turning to shades of red, purple, and even orange. The clusters of flowers are upright and pyramidal and can reach 10” long. As the flowers age, they turn to a lovely shade of pink in the late summer and into fall. Varieties include: Oakleaf and Snow Queen.

Pruning & Deadheading

Hydrangeas are very forgiving and will not suffer if left un-pruned. In fact, young, recently planted shrubs are best left alone. Deadheading spent flowers will encourage new buds to set and bloom throughout the season; cutting blooms actually encourages more flowers. Leaving spent blooms on the plant through the winter adds interest and helps to insulate new buds. Do not prune spent blooms in the spring; you may risk pruning off new flower buds. Unless you are trying to maintain size, pruning Hydrangeas should only be done when necessary and only immediately after the flower is beginning to brown. Any longer after that, you may trim off next year’s flower buds.

Planting of Hydrangeas:

The first step in planning a planting is assessing the plant site and fitting the appropriate plant species to that site. Things to keep in mind for site selection: Soil conditions, sun and wind exposure, what size plant will the site allow, space constraints such as pavement, walkways, buildings, and other trees.

Things to keep in mind for plant selection: Tolerant to the moisture and drainage of your soil, tolerance to sun and wind exposure of your site, what mature size is appropriate for the site?

The Mohawk Valley has a predominately clay soil. This is one of the least desirable soils to grow your plants in. The best thing you can do for your plants would be to have them in a raised bed which will keep the plants main root system above the clay soil, which retains too much moisture, contains no air spaces, and becomes hard packed when dry.

Site Preparation

New landscape beds should be fully prepared prior to planting. This is the time to add extra topsoil, composted manures, etc., with the existing soil. If you are preparing a raised bed it is recommended to till the existing ground area prior to building the site up. If your soil is composed of clay you should add some form of compost at a 1-1 ratio. For sandy soils (usually found north of the Mohawk Valley) mix topsoil and compost at a 1-1 ratio.


The planting hole should be at least 2 times the width of the container. The depth of the hole has to be no deeper than the container.

1.) Find the trunk flare of the plant before you start excavating a hole.  The trunk flare is the area on a plant where the roots start on the trunk. Sometimes you will have to remove some soil to expose the trunk flare, do this after you have the plant in the hole. Excavate a hole using the rule above for measurements. Slope the sides of the hole, increasing the friable soil for vigorous root growth. Remember when planting in clay soil to have the plant raised above the existing soil level by 4-6 inches.

2.) Remove the container gently, prior to planting. Sometimes container-grown plants become rootbound. This means that the roots have become overgrown with in the container. If you notice an overabundance of roots, make some vertical slits down the sides of the rootball and spread the outer roots gently.

3.) Backfill the hole with the amended soil. Do not stamp the soil down too hard. Packing the soil down too hard may make drainage and aeration difficult. A raised ring of soil formed around the edge of the rootball will create a basin that can be filled with water.


Watering is the most important thing you have to do to maintain a properly planted tree or shrub. All new plantings, depending on the weather conditions, will probably need to be watered at least once a week for the next 2-4 weeks. After the initial 2-4 weeks, all plantings should be checked frequently for adequate moisture levels for at least a year (especially during the hot and dry summer and fall months). The easiest and best way to tell if your plant needs water is to make a hole in the soil about two inches deep beneath the plant and feel if there is moisture or not. If the soil feels dry, it is recommended to set a hose at a trickle at the base of the plant until the area is thoroughly wet. Watering time will vary depending on the size of the rootball. You want to water so that the entire rootball is wet. A quick sprinkle from a hose does not provide enough water to seep into the deeper roots.