Hydrangeas

Choose a location where your hydrangea can reach its full size without much pruning. For smaller-sized hydrangeas, expect the plant to reach about 4′ by 4′. Some varieties can reach 7′ tall by 5′ wide.

Hydrangeas planted under a tree often fail to thrive. This is because tree roots are very aggressive and are usually stronger than hydrangea roots. No matter how many of the tree roots you are able to remove to make room for the hydrangeas, the tree roots will all be back in a year or two. Watch plants closely.

Soil Preparation

Plant in well-drained, loose soil! If the roughage such as Utelite, Soil Pep, or Black Forest Compost. In severe cases, plant them on top of a mound, or grow them in containers.

Watering

Place your hydrangea in an area where it can get plenty of moisture. Consistent soil moisture is especially important the first year or two, and during the hot summer weather. Do not over water, especially in clay soil. Too much water can lead to root rot.

Plant Depth

Do not plant too deeply. Plant at the same depth the hydrangea was planted in the pot. Plant in early summer or late fall, not during the heat of summer.

Transplanting

If you want to move your hydrangea, transplant it when it is dormant and has lost all of its leaves (late fall or winter).

Hydrangeas grow best if they are fertilized once or twice each year. Although some gardeners recommend special hydrangea fertilizer mixes to get the maximum results, hydrangeas do amazingly well with many of the common types of fertilizers you normally use. You can add organic material to the soil, such as manure or compost, and apply either an organic or chemical fertilizer.

Organic Fertilizers

Organic fertilizers are excellent because they are naturally slow releasing. The plant benefits from the long-lasting fertilizers. If chemical fertilizers are used, apply a slow-release, balanced fertilizer once or twice a year. Fertilizer such as Rose Fertilizer, Vegetable Fertilizer, Rhododendron Fertilizer or even a 10-10-10 fertilizer will work well if you apply them twice during the spring and summer. Osmocote fertilizer is great but it must be mixed into the soil to release properly for the entire season, don’t just leave it on top of the soil.

Don’t fertilize after August. Fall is the time for hydrangeas to begin preparing for dormancy. Fertilizing too late might stimulate new growth that may be tender.

Amount of Fertilizer to Use

The amount of fertilizer used per plant will vary with the size of the plant. As a general rule, it is much better to err on the side of too little fertilizer than too much. A very small plant will need about 1/8 – 1/4 cup. A very large shrub will need 2 – 3 cups, spread around the drip line of the branches (not just next to the trunk). Read the fertilizer label to determine exactly how much fertilizer you need to apply.

Never fertilize a plant that looks sick or wilted. If a plant is struggling due to a disease or root problems, the fertilizer will only add stress to its life. Try to cure the problem before adding fertilizer.

Finally, to give your hydrangea the best chance for maximum blooming, fertilize your plant once or twice during the summer with Fertilome Blooming and Rooting Fertilizer. This liquid fertilizer will give your plant instant access to those elements that will promote large blossoms, especially to the pink varieties.

Established bigleaf, panicle, oakleaf and smooth hydrangea plants can often benefit from regular pruning. Removing about one-third of the oldest stems each year will result in a fuller, healthier plant. This type of pruning is easiest to do in winter, since the absence of leaves makes it easier to see and reach inside plants.

Gardeners may also want to prune to control height or to remove old flower heads. The best time for this type of pruning differs between species. Bigleaf and oakleaf hydrangea, which flower on previous year’s growth, should be pruned shortly after flowering is complete.

Prune panicle and smooth hydrangea flowers on current year’s growth. They can be pruned anytime from late summer until early spring. If pruning these two species in the spring, try to prune before leaves appear. Plants of hydrangea arborescens ‘Annabelle’ have been known to produce a second flush of flowers if pruned lightly after the first flowering.

While hydrangeas in landscape settings are relatively pest free, under certain growing conditions some diseases and insects can become problems.

Powdery Mildew

For the bigleaf hydrangea, the major disease problem is powdery mildew. It is most common on plants growing in shade and under high humidity conditions. Powdery mildew infested leaves are covered with a light gray powdery- looking substance. Purple splotches may also appear. Powdery mildew rarely kills plants, but it is unattractive.

Fungus

There are several fungal leaf spot organisms that attack hydrangea. Leaves develop brown to gray lesions surrounded by purple halos. These leaf spots are most common in late summer and early fall, and seem to be more common among plants grown in sunny locations. Again, plants are rarely killed, but severe infestation can be very unattractive.

Some hydrangea are susceptible to rust, which will appear on the back side of leaves as small, orange spots. Rubbing the back of the leaves will release an orange dust which contains spores of the fungus. The disease is usually seen near the end of the growing season and rarely kills plants.

Some hydrangea are susceptible to rust, which will appear on the back side of leaves as small, orange spots. Rubbing the back of the leaves will release an orange dust which contains spores of the fungus. The disease is usually seen near the end of the growing season and rarely kills plants.

It is important to prevent leaf diseases rather than try to cure them. If your hydrangea is prone to any of these diseases, spray with a fungicide once a month to prevent them. You may need to spray every two weeks to control a disease once it starts to appear.

Root Rot

Some hydrangeas are susceptible to root rots. The most common is Armillaria root rot. Infested plants will appear wilted, but will not recover when watered, and they will eventually die. Planting hydrangeas in poorly drained soils will increase the incidence of root rot and should be avoided.

Insects

Aphids can be a problem on the new growth of all hydrangeas, but can be easily controlled by washing, using an insecticidal soap, or spraying an insecticide. The presence of ants crawling on plant leaves is often an indicator of an aphid problem. The ants feed on the sticky honeydew (excrement) left by the aphids. If you see ants on the leaves of your hydrangeas, turn the youngest leaves on the plant over and look for small green insects. As leaves become tougher during the growing season, aphid problems usually diminish.

Mites can cause problems on hydrangeas. Mites are too small to see with the naked eye, but mite infestation can cause distorted growth, mainly seen in new shoots. Webbing between leaves will also be noticed with spider mites. Mite problems are usually worse during hot, dry weather. Adequate watering of plants during hot weather is the best preventative against mite problems. Mites are difficult for the homeowner to control using insecticides.

Cut Flowers

Hydrangeas make excellent cut flowers and the dried blooms make beautiful arrangements. The key to successfully drying hydrangeas is to cut them at the right time.

Drying Hydrangea Blooms

Unfortunately, it’s difficult to dry hydrangea blooms that have been cut at their peak of color. For best results, allow the blossoms to dry on the plant before cutting them. Do not collect them until the flowers have developed a papery feel.

After collecting the blooms, they can be placed in a dry, airy room out of direct sunlight until fully dried. They may be left standing in a dry vase or hung upside down. Either method works well. Strip off all leaves and then find a dry place indoors where the flowers can finish drying. Some people recommend using a warm, dark location, such as an attic. Others prefer a cool, dry location. Whichever method you choose, be sure to keep individual inflorescences separated as they dry so that none of the flowers get squashed. The flower heads of some cultivars dry better than others.

The method used to dry them isn’t nearly as important as the timing for gathering the blooms.

Indoor Holiday Plants

Most of the ‘florists’ Hydrangeas, that are sold as potted plants, are a delicate variety of Hydrangea macrophylla. Most florist hydrangeas will not produce flowers when planted outside, because their buds are not cold hardy.

If you receive a potted hydrangea for Easter or Mother’s Day in full bloom, keep the soil moist at all times, as this plant has a high water requirement and tends to dry rapidly in the home. It should also receive direct light. After the flowers fade, they may be removed and the plant treated as a house plant. When danger of frost is past, you can try planting it in a sheltered location in the garden. Shelter is necessary because the hardiness of this plant is questionable. This plant forms flower buds in the fall, like forsythia and wisteria. If these buds freeze, the plant will survive and produce green leaves, but no flowers.

Planting in a sheltered location, plus covering the plant with burlap, will offer some protection. If you wish to improve the probability of flower bud survival, you may wish to try protecting them even more. Before the temperature falls to 25 degrees F, place a screen around the plant. Fill this with an insulating material such as coarse peat moss, vermiculite or bark. More material may be added if it settles during the winter. Remove this protection when the crocuses flower but you must still protect them on cold nights. If you are lucky, the flower buds will survive. If not, you should still have a pretty foliage plant.

Proper hydrangea winter care will determine the success and quantity of next summer’s blooms. The key to hydrangeas winter protection is to protect your plant prior to the first frost of winter, and through the last frost the following spring.

The first step in hydrangea winter care is to cut away the old wood at the base of the plant, and remove any dead or weak branches. Be careful not to cut off healthy wood, as this wood will be where your hydrangea will bloom from next year.

Make a frame around the plant by using stakes. Wrap chicken wire around the stakes to form a cage. Fill the cage with bark or leaves to fully insulate your plant. Be careful not to snap off the ends of the branches as you fill the cage, or you won’t have those gorgeous blooms next summer.

Protecting hydrangeas from winter cold and wind can seem labor intensive. However, once you have your plant’s winter home in place, the remainder of the winter will only require a little housekeeping to maintain successful hydrangea winter protection.

Hydrangeas are fascinating in that, unlike most other plants, the color of their flowers can change dramatically. It would be nice if one could change the color of hydrangeas easily, but for most of us, it is not easy. The people who have the most control over the color of their hydrangeas are those who grow them in containers. It is much easier to control or alter the pH of the soil in a container than it is in the ground.

There are a few facts to remember.

• Not all hydrangea varieties can change color. Those that are naturally white will remain white no matter what soil type they’re grown in.
• If your plant is in a hot climate, it is unlikely you will ever see a “true red” hydrangea. No matter how convincing those pictures in the catalogs are, or how much lime is added to the soil, you can only achieve a very deep or dark pink, but not a true red.
• It is much easier to change a hydrangea from pink to blue than it is from blue to pink.
• Hydrangeas often change color on their own when they are first planted, or transplanted. They are adjusting to their new environment. It is not unusual to see several different colors on one shrub the year after planting.
• One can rarely change the intensity of a color (how strong or pale the color is). The intensity develops for a number of reasons: the heredity of a particular hydrangea variety, weather conditions (hot or cold, humid or dry), health of the plant, and possibly other natural factors.
• There are a few cultivars that never produce blue flowers. In low pH soils, flowers of these “non-bluing” cultivars turn a dull reddish-purple. In higher pH soils, the flowers of these cultivars are a vivid deep pink color. Some non-bluing cultivars are ‘Alpengluhen’, ‘Pia’ , and ‘Kardinal’.

Color Confusion

The actual hydrangea flower is small and insignificant but is surrounded by showy, colorful bracts. The anthocyanin pigment will be either pink or blue, depending upon the amount of either iron or aluminum in its molecules. Insufficient aluminum is absorbed by the plant at a pH of 6.5 to 7.0 so the plant uses iron instead.

As the pH drops to 5.0 to 5.5, aluminum becomes more soluble. It is absorbed by the plant and becomes part of the anthocyanin molecule resulting in blue coloration. The molecule uses less iron. The actual color of the pink and blue varies and is determined by the degree of soil acidity. White hydrangeas contain no pigment in their sepals (although some may develop as the blossom ages). They may be grown as either pink or blue, the only indication being given by the small petals.

Change Blooms to Pink

For hydrangea blooms to be pink, the plants must not take up aluminum from the soil. If the soil naturally contains aluminum, you must try to keep it away from the hydrangea’s system. Following are a few tips that might help:

• Add dolomitic lime several times a year. This will help to raise the pH. The pH should be about 6.0 to 6.9 (If it goes above 7.1 hydrangeas may experience an iron deficiency). Since hydrangeas take up aluminum best at lower pH levels, raising the pH will help to keep the bluing effect of aluminum out of the hydrangea’s system.
• Use a fertilizer with high levels of phosphorus. Phosphorus helps to prevent aluminum from entering into the system of the hydrangea. Choose a fertilizer close to the ratio of 25/10/10 (Phosphorus is the middle number).
• In areas that naturally produce blue hydrangeas (soils with a lot of aluminum), consider growing pink hydrangeas in large pots. In a pot, it is much easier to control the requirements for growing pink hydrangeas.

Change Blooms to Blue

To obtain a blue hydrangea, aluminum must be present in the soil. Most garden soils have adequate aluminum, but the aluminum may not be available to the plant if the soil pH is high. To ensure that aluminum is present, add aluminum sulfate to the soil around the hydrangeas. Some gardeners also recommend that a solution of 1 Tbsp aluminum sulfate per gallon of water be applied to plants (which are at least 2-3 years old) throughout the growing season. Important: Do not apply the mixture on leaves, and water plants well in advance of application. Put this solution on cautiously, as too much can burn the roots.

To make the aluminum already in the soil available to the plant, the pH of the soil should be low (5.2-5.5). Adding sulfur will tend to lower the pH of the soil. Another method for lowering the pH is to add organic matter to the soil such as coffee grounds, peat moss, acid planting mix, grass clippings, etc. If the soil naturally contains aluminum and is acid (low pH) the color of the hydrangea will automatically tend toward shades of blue and purple.

The choice of fertilizer will also affect the blue color change. A fertilizer low in phosphorus and high in potassium is helpful in producing a good blue color. Superphosphate and bone meal should be avoided when trying to produce blue hydrangeas.

Planting hydrangeas near a concrete foundation or sidewalk will often affect the color since the pH of the soil may be raised considerably by lime leaching out of the concrete, making it difficult to have the blue color.

While these methods of changing the flower color can be used, you risk severely altering the soil pH incorrectly, thereby making it difficult for the plant to utilize other nutrients. You can also affect other, non pH adjusted plants, growing nearby. The pH of a soil is very important to all plants, not just hydrangeas.

Always get the soil pH tested before trying to change it. If you really like different colors in your hydrangeas then plant many different cultivars together!

While there are approximately 23 species of Hydrangea grown throughout the world, and new varieties are developed all the time, there are three that do well in northern Utah.

Hydrangea paniculata is the most cold hardy member of the hydrangea genus. It can be reliably grown in zones 4 to 7. It is native to Asia. It can grow 10 to 15 feet tall. It has large, creamy-white flowers, which are borne in 6- to 18-inch long panicles, and are produced in mid-summer. As flowers mature, they may turn pink. Plants, particularly those of the cultivar H. ‘Pee Gee’, are sometimes pruned into a tree form. Hydrangea paniculata is also suitable for use in a mixed border or as a deciduous hedge.

Hydrangea quercifolia – Oakleaf hydrangea is one of two hydrangea species that are native in the U.S.. Plants generally grow 6 to 8 feet in height, although a few cultivars with smaller growth habits are available. Large panicles of creamy white flowers (4 to 12 inches) are produced in early summer. As flowers age, they often turn a medium- to deep-rose color. Oakleaf hydrangea is the only member of the genus to develop significant fall foliage color. Leaves turn a deep mahogany-red and stay on the plant until late fall. Exfoliating bark adds to winter interest. Oakleaf hydrangea is best used in a mixed border, or as a mass planting. They are hardy from zones 5 to 9.

Hydrangea arborescens – Smooth hydrangea is the other U.S. native. In cultivation, plants usually reach about 5 feet in height, with a similar, or greater, spread. The species is rated as hardy from Zones 4 to 9. Flowering occurs in early to mid-summer. The most common cultivar, ‘Annabelle’, produces rounded inflorescences that may reach up to a foot in diameter. Plants may also have a lacecap type inflorescence consisting of a combination of a few large, and many small, flowers. At the peak of flowering, smooth hydrangea flowers are a pure white. As they age, they develop a pale green color. Smooth hydrangea is extremely striking in mass plantings.

Hydrangea anomala ‘petiolaris’ – Climbing hydrangea is not as well-known as the previous four species, however it is becoming more popular. It is hardy from zones 4 to 7. Climbing hydrangea is a true clinging vine. While initially slow growing, the plant can eventually cover tall (up to 80 feet) structures. White, lacecap type inflorescences are produced in early- to mid-summer. Plants can be slow to start flowering, but patience is rewarded by a spectacular floral display on established plants. An alternative to planting climbing hydrangea on the side of a building, is to allow it to climb up a tall tree or to cascade over a horizontal surface like a rock pile. Climbing hydrangea grows well in shade, but can also tolerate a sunny location.

 

If you would like to try a more carefree hydrangea, try the Hydrangea quercifolia – Oakleaf Hydrangea. It is a beautiful shrub for all seasons of the year. It has white flowers in the summer that fade to shades of pink and brown as they mature. The leaves turn red in the fall before they drop. The shrub has a beautiful open shape and brown, exfoliating bark that adds interest to your garden in the winter. It prefers light to medium shade, but tolerates sun or moderately dense shade.

Another easy hydrangea is H. paniculata. It is a large shrub that can be trained into a small single or multi stemmed tree. Flowers are generally white, but some tend towards pale pink or green, depending upon the cultivar.