Hydrangea macrophylla, also called bigleaf or French hydrangea, has either pink or blue flowers. Flower color is determined indirectly by the soil pH, which affects the availability of aluminum in the soil. In acid soils the flowers will be blue, in alkaline soils the flowers will be pink. Aluminum is available to the plant in acid soils. Research has determined that the actual mechanism of color variation is due to the presence or absence of aluminum compounds in the flowers.
For blue flowers, maintain a soil pH between 5 and 5.5. Apply aluminum sulfate or sulfur to reduce the pH to this range when you see new growth emerging in April.
For pink flowers, maintain a soil pH of 6 or more by liming your soil.
Hydrangeas are deciduous shrubs that grow from 4 to 12 feet in height depending on the variety.
The growth rate is quite fast.
Bigleaf hydrangeas are effective as single plants, massed or in containers on paved terraces.
Hydrangeas are easy to grow in well-drained soil, which should contain plenty of organic matter or humus.
Bigleaf hydrangea prefers morning sun and afternoon shade. Avoid planting it in hot, dry, exposed sites. Most people buy hydrangeas when they are blooming, but spring or fall is the best time to set them out. For planting, dig a large hole approximately two feet across and one foot deep.
Bigleaf hydrangea responds to several light applications of fertilizer during the growing season. A general-purpose fertilizer, such as 10-10-10 applied at a rate of 2 cups per 100 square feet in March, May and July is suggested. It is not necessary to remove the mulch when fertilizing, but water soon after application to help dissolve the fertilizer and send it into the soil.
Hydrangeas have such big leaves that they can suffer if set out during hot weather. They need plenty of water, so plan to water thoroughly once per week or more frequently.
Bigleaf hydrangea should be pruned after flowering so they can develop "old wood" to support blossoms the following summer. Avoid pruning after August 1.
One of the easiest ways to propagate bigleaf hydrangea is by layering. This is done by digging a trench near the plant and bending a section of limb down into the trench. Use a knife to remove a small ring of outer bark about an inch wide all the way around the limb. Then, cover the limb with soil, leaving 6 to 12 inches of the tip growth uncovered. Old established hydrangeas may also be divided in the early spring by using a shovel to divide the clump.
The most common reason for hydrangeas failing to bloom is winter injury. Other reasons may be too much shade, poor fertility and too much nitrogen fertilizer.
Hydrangeas are susceptible leaf spots and powdery mildew. Insect pests on hydrangea include aphids, leaf tiers, rose chafers and red spiders.
CULTIVARS AND VARIETIES
The cultivars of Hydrangea macrophylla are divided into two groups:
- The "hortensias" have sterile flowers in solid masses, which are often so heavy they cause the stem to bend.
- The "lacecaps" have a center of fertile, relatively non-showy flowers and an outer ring of showy, sterile flowers, which together form a pinwheel effect.
- All Summer Beauty, 3 to 4 feet tall with flower heads produced on current season growth, unlike other bigleaf hydrangeas.
- Carmen, 4 feet tall with large pink flower heads.
- Nikko Blue, 4 to 6 feet tall with rich blue flower heads (in acid soil).
- Blue Prince
- Compacta, supposedly more compact than Nikko Blue with darker green leaves.
- Blue Wave, 6 to 7 feet tall with lacecap flowers.
- Coerulea, perfect flowers a deep blue and ray flowers blue or white.
Several lacecaps feature silver-variegated foliage: Quadricolor, Silver Variegated Mariesii, and Variegata.
Oakleaf Hydrangea (Hydrangea quercifolia): This deciduous shrub grows to 6 feet tall and has deeply lobed, oak like, 8-inch leaves, which turn bronze in fall. The white flowers turn pinkish as they age.
Snow Queen‚ has large white flower clusters. Snowflake has a double-flowered appearance. Harmony is a low-growing shrub, 3 feet tall and 6 feet wide, with spectacular 12-inch cones of sterile flowers.
Climbing Hydrangea (Hydrangea anomala): This is a deciduous vine, which climbs high by clinging aerial rootlets. Leaves are roundish, 2 to 4 inches long. The white flower clusters are 6 to 10 inches wide in lacecap effect. Old plants have a peeling, cinnamon-colored bark.
Smooth or Snowhill Hydrangea (Hydrangea arborescens): This is a 5-foot-tall deciduous shrub with oval, grayish green, 4- to 8- inch leaves. Flowers are dull white and bloom late June through September.
Annabelle produces enormous (to 1 foot) globular clusters of sterile white flowers on a plant about 4 feet tall.
Grandiflora has 6-inch clusters on a similarly sized plant.
Peegee Hydrangea (Hydrangea paniculata): This is a 10- to 15-foot shrub or up to 25-foot tree. Leaves are 5 inches long and turn bronze in fall. Flowers are mainly fertile, in 10- to 15-inch clusters, white slowly fading to pink in fall. Peegee hydrangeas are tolerant of city conditions and grow well in seaside gardens. Tardiva flowers later, in August and September. Praecox grows 10 to 15 feet tall and flowers in June.
Hydrangea serrata is a small (to 5 feet tall) deciduous shrub similar to H. macrophylla but smaller, with smaller leaves and smaller flowers.
Blue Billow is only 3 feet tall.
It's best to wait to plant until the last chance of frost or severe heat has passed so that the plants have the best possible chance at survival. A late frost can nip the buds and reduce the number of blooms. There isnít one universal answer for planting time and it really depends on your weather. If your weather is over 85 degrees consistently, itís probably too warm. If your temperatures are less than 40 degrees, itís probably too cold. The most active growth period for hydrangeas is April through September and if they must battle heat or cold to get their get their root systems established, it may be too much for them to do both vital tasks.
For planting, choose a location that does not get hot afternoon sun. New hydrangeas donít like much direct sun even if they are able to take full sun once established. Prepare a hole two or three times the size of the root ball. The poorer your soil, the bigger the hole should be. Hydrangeas like slightly acid soil (pH of 4.5 to 6.5). If your soil is heavy, incorporate some humus-rich material (potting mix, peat moss, perlite, bark dust or compost) with the dirt you took out of the hole. Back fill the hole as you plant such that your finished job leaves the surface (top of the root ball) about 1" above the original soil level. If planted correctly, the settled new soil will not leave a depression for water to stand in. Thoroughly water the plant and keep moist in hot weather until well established. Use a bi-annual application of balanced fertilizer keeping an eye on how it may affect your soil pH levels.
You may move hydrangeas as well. Be sure the plant is well established before trying this transplant method, as a strong root base is essential. Once the plant is finished blooming in the fall before it's dormant, prune the hydrangea. Tie the branches together with twine to prevent damage. Dig up the roots of the hydrangea and be sure you dig a large root ball containing lots of roots. Replant the hydrangea immediately and water well. You may also divide a hydrangea using a sharp spade. Colors may be slightly different in the year following the transplant. Spring transplanting is always acceptable, too. Same directions but donít prune the hydrangea drastically.
Drainage and good soil
We always talk about the importance of good soil for hydrangeas and its ability to drain well. Most areas donít have perfect soil but there are lots of things you can do to improve your soil and grow better hydrangeas. Good soil is important for root growth and supplying water to the hydrangeas leaf and stem structure but most importantly, the flowers. Here are a few tests to see what kind of soil you have in your garden.
Drainage test Ė Dig a hole about 6 inches deep and one foot wide and fill it entirely with water. Let the water drain out of the hole completely. Fill the hole again and record the time it takes to drain the second time.
If the water drains in three hours or less, your soil is most likely draining too quickly. Chances are your soil is somewhat sandy. If the water drains in four to six hours, your soil is draining just perfectly. You have rich, great soil for hydrangeas. If the water drains in eight hours or more, the soil has poor drainage typically common with clay-like soil.
Root test Ė Dig gently around a selected plant, preferably an annual weed or something that was going to be moved and thrown out anyway. Pull out the plant from the soil gently making sure that the root system stays intact. Check the root system of the plant. If there are many fine strands of roots that are bright white and healthy in appearance, you have great soil. If the roots are stunted, lopsided or otherwise dingy, your have poor soil.
Compaction test Ė Spear a wire rod (we use a 4mm or ľĒ gauge wire) into the soil. Mark the depth of penetration Ė the sooner it bends, the more compact the soil. The ideal condition for shrubs is about one foot.
Dirty Thumb test Ė Dig a hole about 6 to 10 inches deep. Separate a section of your soil, intact, about the size of your two palms cupped together. Is your soil granular, powdery or clumpy? The best type of soil will clump in small but breakable consistencies.
Letís say you your soil didnít pass one test or passed very few tests. Here are some great components that can be added to improve your soil: Grass clippings, clean and disease free leaves, homemade compost, well-aged manure, mushroom compost, store bought potting mix, perlite or peat moss. Mix these into the soil in early spring a few weeks before you begin planting. For more information, call your local university extension office. Our local customers can call the Oregon State University Extension office at 541-737-2513 and ask about the Willamette Valley Soil Quality guide. The cost is $3.
Sudden Oak Death
According to up-to-date studies, Sudden Oak Death (SOD) doesnít affect hydrangeas and the hydrangea genus is not a host species. The US department of Agriculture has deemed 28 plant families as natural hosts for Phytophthora ramorum, the fungus like organism that has been found to cause Sudden Oak Death. Commonly found hosts are Rhododendron, Pieris and Camellias.
Pests & Disease
Slugs and snails are the most common pests. They seem to be attracted to the lighter colored leaves and the thinner leafed varieties. Our recommendation is get some slug and snail bait. There are many brands that are not harmful to pets or children (Sluggo and Worryfree). Weíve had the best luck with Deadline. There are some new brands on the market that are made with iron phosphate that actually help plants grow. As for natural solutions, you may pick them off and cut them with sharp pruners early in the morning before the sun is completely out. Some other less tiring methods are broken eggshells, a small flat container full of fresh beer, a 2-liter plastic bottle with the top cut off with just a little beer at one end, or add frogs and toads to your garden Ė they love slugs and snails.
Deer like to eat hydrangeas and have been known to love the Arborescens and macrophylla varieties best. Fencing or wire cages are the best defense again deer. There are some repellent sprays on the market but they must be applied often.
Thrips and spittlebugs may suck the moisture out of leaves. These pests love the shady areas best. Any garden insecticide will take care of these critters. Read all application instructions thoroughly and to ensure that the pesticide is safe for hydrangeas.
Powdery mildew and black spot may occur in shady locations when the hydrangea gets poor air circulation. Keep overgrown plants a good distance away from the base on the plant and discard any leaves with traces of mildew or fungus. Rust spots occur with too much direct sunlight after overhead watering. Itís best to water in early morning or late afternoon to allow the leaves to dry before the hot afternoon or cool night.
When to prune is mostly a matter of convenience. We have pruned both in the fall and early spring and had good results either way. It does seem that the later and the more harshly you prune that fewer flower blooms can be expected the next season. This is because most hydrangeas bloom on "old" wood. With young plants, be sure to prune enough growth to form them into a good "shapeĒ and no more. This is generally 10 to 20 percent of the growth.
Unlike many of your other flowering bushes (roses and buddleia), hydrangeas should not be harshly pruned in the spring. Most hydrangea varieties bloom on old wood and if you cut too much, you wonít get any blooms. We recommend fall pruning after blooming is done. For us here in the Pacific Northwest, that means October. This allows for some active growth before the plant goes dormant.
If you miss fall pruning, you can still prune in the spring. Once your plant starts to leaf out and your last hard frost is about two weeks past, you can see the leaf nodes beginning to form. Count back from the end of the plant such that you have at least three fat and healthy leaf nodes forming. Prune right above the third one. You may want to wait until leaves are starting to show before you prune your macrophyllas so you donít prune too much.
The Paniculata and Arborescens varieties bloom on new wood so you may cut them for size every year, spring or fall, whatever is most convenient for you.
The color of hydrangeas will vary considerably due to the pH of the soil they are growing in. The blue hues are best in acid soil and the degree of blueness is controlled by the amount of available aluminum and the capacity of a particular variety to draw it up. The reds and pinks enjoy an alkaline or neutral soil where aluminum is not actively absorbed. The whites stay white but usually enjoy the same conditions as the reds and pinks.
To encourage "bluing" of the flowers, you need to raise the acidity of the soil. Acidity levels need to be around 5.5 - 6.0 on the pH scale. To lower the pH and increase the amount of aluminum in the soil, apply around the hydrangea aluminum sulfate several times at intervals in the spring and again in the fall if the desired color is not achieved. The amount of aluminum sulfate really depends on the concentration. You donít want to over do it because aluminum is toxic in large doses.
Aluminum occurs naturally in most soil. If you can get the pH lower, the plant may absorb some on its own. Testing your soil for trace elements (including aluminum) is highly recommended. There are many tests available on the market for pH, too. Increase the pH of your soil by applying sulfur, rusty aluminum nails or pennies, citrus fruit peels, coffee grounds, evergreen tree needles or bark. Fertilize with a product that is very low in phosphate. Phosphate limits the absorption of aluminum.
For a powder form of aluminum sulfate, my general rule is ľ cup per foot of hydrangea. This means that for an established 4-foot hydrangea, 1 cup of aluminum sulfate spread around the base of the plant should be adequate. This assumes a 15% concentration mixture of aluminum sulfate, the most commonly sold concentration. You may mix the aluminum sulfate in water and dissolve or apply straight to the plant then water in well. Be sure that the plant has established itself before application. We donít recommend aluminum sulfate for new plants because of toxicity.
Apply in the early spring when you see the first leaf. Apply again six weeks later. If color isnít as desired, add a fall application too.
To encourage pink to red blooms on plants in high acid soil, apply lime to the soil. The lime should be applied at the rate of one pound to every ten square feet of surface area once or twice a year until the desired bloom color is obtained. You may also use a fertilizer high in phosphate, as that will also limit the absorption of aluminum.
Note color correction takes some weeks or even months for the desirable changes to take affect. Some varieties will not get darker.
If your hydrangeaís leaves are lush and green but don't have any blooms, it could be that you're fertilizing too much. Hydrangeas bloom best if they are a little stressed. High nitrogen-based fertilizers can actually inhibit blooms on most varieties. Hydrangeas donít like to be overfed with fertilizers. Some hydrangea growers never feed their hydrangeas and have great blooms and healthy leaves. However, some must feed every few months to maintain the healthy plant. It really depends on your soil and the nutrients that are found naturally in your soil. Luckily, hydrangeas are such wonderful plants, they will tell you what they need.
As a general rule, we recommend fertilizing twice: early spring and early fall. Use a time-released fertilizer that releases slowly (by water or temperature or both) over a 4 to 6 month period. A commonly available product is called Osmocote but there are other brands that are equal. The general blend that yields 10-10-10 or 16-16-16 is all you need. There is no need to run out and buy a special fertilizer for every variety of plant in the garden. This particular mix is great for everything.
There are some fertilizers just for acid loving plants available on the market. These are a great instant boost for plants but tend to be very high in nitrogen and may actually inhibit the ability for the plant to bloom. Too much nitrogen and the plant will focus on stems and roots Ė which is not a bad thing. However, you bought these plants to bloom so there needs to be a balance.
Our recommended use for these instant fertilizers is for emergencies only. In May or June (depending on your area) hydrangeas begin to set bud and grow very quickly. The hydrangea will begin absorbing nutrients from the soil at a very rapid pace. If your soil doesnít have enough nutrients, hydrangeas may get yellowing leaves on the inside parts of the plant. This is a perfect time for the instant fertilizer when the hydrangea needs it most.
What do your hydrangeas need in terms of fertilizing? The three essential components of fertilizer are nitrogen, phosphorus and potassium, the N-P-K numbers on any fertilizer. Nitrogen is for healthy green growth by helping the plant to grow chlorophyll. Fertilizers high in nitrogen like 25-10-10, is great for greening up your lawn. Phosphorus helps a plant grow good roots and stems in the early growth season then in flower production. A mix like 10-30-10 is great for flowers on your annuals and perennials. The Potassium (K) helps your plants generate and process nutrients. Other important elements in fertilizers are calcium, magnesium, iron, copper, manganese, zinc, and sulfur. Organic fertilizers are usually very low in these trace elements.
Hydrangeas like a balanced fertilizer. We prefer the granular time-released kind that delivers nutrients to the plant constantly for a 3- or 4-month period. Water will break down the outside coating of the fertilizer slowly and nutrients wonít dwindle out in the active spring growth season. Be sure that the soil is slightly moist when applying the granulated variety and keep the fertilizer off the foliage to prevent burn.
For blue hydrangeas, a low phosphorus element (the ĎPí) is important as too much will limit the plantís ability to absorb aluminum. The amounts of sulfur (lowers pH) and calcium (raises pH) are important to keep the blue color. A good soil test from your local garden center can tell you what elements are missing from your soil.
Drying & Cutting Blooms
It has been our experience that hydrangea blooms will not dry when freshly flowering. For drying, the flower heads need to be of a "papery" consistency. This is usually towards fall before the first frost or well into the bloom's life. Pick the leaves off the flower stems and hang them upside down for a few days in a dark, warm place. Sometimes it helps to use a fan for air circulation. Store or arrange the dried blooms in a dry place away from direct sunlight, as this will fade the color. You may even spray paint them once they've dried completely.
We are not experts at cutting but asked our friendly cut flower guy his tricks of the trade. The trick is to eliminate the oxygen bubble from the stems. Here are his tips.
Donít cut fresh blooms: Be sure that the hydrangeas are at least a few weeks old. The older the bloom, the longer it will last. Color pigments should be fully developed before cutting.
Cut all the leaves off: Leaves take moisture away from the flower head so strip the leaves off before cutting. Long stems are nice for vases but the longer the stem, the less water that reaches the bloom.
Immerse cut blooms immediately in water and soak for two hours: this may require that you weigh the hydrangeas down in the water. Cold water that has been boiled works the best because it has less oxygen.
Some other methods for cuts that eliminate the oxygen bubble in the stem:
Florist gel is expensive, time consuming and can be messy but works
Put the cut ends in boiling water
Smash the cut end with a hammer right after cutting
Cut another inch off the stem underwater
Propagation and Multiplying Hydrangeas
You may also propagate by layering long droopy branches directly onto the soil or by hardwood cuttings but our most successful method is soft- or semi-softwood cuttings. June and July is the best time for the soft cuttings. Hereís how:
Using sharp clean clippers, cut just above the third leaf node from the end of the stem. Cut off the leaves from this cutting at the node closest to the bottom. Cut in half the next set of leaves. Place the whole stem in well draining potting mix. Keep the cuttings warm, out of direct sunlight and moist but NOT wet. In about two to four weeks, roots should begin to grow and you can transplant into a container.
This works on most macrophylla type hydrangeas. The harder stemmed varieties, Petiolaris, Aspera, Involucrata, Oakleaf and Paniculata will require some rooting hormone to root.
Hydrangeas produce seeds in November and December and can be used once the hard outer shell is removed. We do not grow from seeds, as varieties do not consistently reproduce themselves this way.
I've found that forced hydrangeas aren't as healthy as naturally grown hydrangeas. They grow better if they are allowed to have a dormant period and a growth period. Most varieties grow very quickly and may not be healthy if grown inside without moving the plant to a larger pot. When your forced blooms begin to decline and cannot be revived with water or moving to a larger pot, it is time to cut off the blooms and the lowest healthy leaf node. Instant fertilizer for acid loving plants is great for these forced hydrangeas that start to look peaked.
Hydrangeas like slightly acidic soil too. In the artificial media that most of these forced plants are grown, you'll need to keep the acidity level up (i.e., the pH level down). Tea leaves, coffee grounds or aluminum sulfate can help because they are acidic.
If you do move it outside, be sure that you don't move it until the last chance of cold weather has passed and there is no chance of any frost. My general rule of thumb is don't move the forced hydrangea outside until the outside hydrangeas are at the same stage of leaf. That can be April, May or June, depending on your area.