Introduction
Hydrangea is a common deciduous shrub that produces large heads of clustered flowers. It is a highly desired cut flower for use in floral arrangements. There are numerous types of hydrangeas, but the most common is the Hydrangea macrophylla which consists of the mopheads and lacecaps. These hydrangea have thick, crisp leaves with toothed edges. Other types are the PeeGee, which grow into small trees and the Oakleaf which has foliage that reddens in the fall. Hydrangeas typically flower from summer to fall and prosper in zones 4-9.
Flower color depends largely on the pH of the soil and not the variety of the plant. An acidic soil with a pH level of 4-5.5 will have higher aluminum content leading to a blue colored flower, but a neutral or slightly alkaline soil will result in a pink colored flower. Adding aluminum sulfate to the soil will increase the acidity and produce blue flowers and adding lime will create an alkaline soil and pink flowers. The flowers can vary from blue to purple to pink or any combination of those colors. Optimal soil conditions for hydrangeas are a moist soil with proper drainage that is rich in nutrients.
Cutting Propagation
Stock Plant Considerations:
The stock plant should be actively growing under optimal nutrient and environmental conditions to ensure the best rooting of cuttings. Cuttings should be taken from a stock plant that is free from disease and pathogens. Any disease in parent material will infect and kill cuttings. Tools should be properly sanitized between stock plants to prevent any transfer of disease or pathogens.
Selecting a cutting
The first step is to identify a proper cutting. The ideal cutting will be a stem with no flower that is new growth. New growth will be a lighter color. Colder climates force hydrangeas to die back every year, so all growth will be new growth in this case. The time to take a cutting would be fall as the plant is going dormant, but still has leaves. The cutting should be taken in the morning when the plants are the most turgid because they will have the highest water and nutrient levels at that time. Cutting material with a small degree of flexibility is desired, but not real tender material because it will desiccate faster. Ideal material would be able to bend, but will break when bent sharply.
Steps:
Image from: http://hydrangeashydrangeas.com/propagation.html
1. After a proper stem for cutting has been identified, a 4-6” cutting is taken just below a leaf node which is where the leaves grow out from the stem. The cutting should have at least 2 nodes on it. (see picture #1)
2. All but the top set of leaves should be stripped from the cutting. (see picture #2)
3. Cut the remaining leaves crosswise, not lengthwise to about half their original size. This is done to decrease the surface area and use of energy when the cutting will be trying to develop new roots. (see picture #3)
4. Dip the cutting into auxin, a rooting hormone. Most common application is 1000 ppm IBA or NAA. This step is entirely optional because the cutting will root without the hormone. However, utilizing the rooting hormone will result in quicker root development.
5. Place the cuttings into the damp, sterile material of your choice. Vermiculite, potting soil or sand can be used.
6. Cover the pot with a plastic bag. Be sure to use stakes to prevent the bag from touching the leaves.
7. Place the cutting in a sheltered location out of direct sunlight. The cuttings need a well-lit area, but the direct sunlight will cook them in the plastic bags.
8. Check the cuttings daily to ensure the soil is damp and there is no signs of disease or pests.
Do not water the cuttings until the soil begins to feel dry to prevent overwatering and rotting.
The cuttings will begin to develop roots within a few weeks. If you can tug on the cutting without removing it from the soil, it has a substantial root system developing. After a few months the cuttings should be rooted and ready to be sold or planted to become future stock plants.
Other Propagation Methods
Seeds:
Hydrangeas can produce beautiful flowers, but rarely produce seeds. This is why seed propagation is not a common way to propagate hydrangea plants. Seed propagation can be easy, but the seedlings do not always display the desired characteristics.
Ground Layering:
Ground layering is a very easy method to propagate hydrangea, but is severely limited by the number of stock plants. A branch or several branches close to the ground are selected. About 5-6 inches of leaves are removed to create an area to bury. The cleared area is scored on the side touching the ground and at least one leaf node is placed in 2” trench and covered with soil. The roots will sprout from the leaf node. The branch stays attached to the parent plant until roots have properly formed. A brick or similar object are placed on the buried area to prevent the stem from standing back up.
The roots will form quickly, but the plant may experience shock when detached from the parent plant and will require additional care and attention. One possible solution to this problem would be to keep the cutting buried for few weeks after it is detached from the mother plant. The limitations of this type of propagation are the main reason cuttings are used more often.
Pot Layering:
Pot layering is similar to ground layering, but instead of burying the cleared area in the ground it is placed in a small trench in a pot. The pot is cut down both side to allow the stem to lay across it without damaging it. The plant is then cut from the parent plant as it would be with ground layering, but the shock seems to be decreased. This method may help reduce the stress to the cutting, but is still limited by the number of available plants.
In-vitro Propagation:
There is not much information available on in-vitro propagation for hydrangeas, but there is research being conducted about the effects of sterilizers and hormones on hydrangea tissue. It is hypothesized that tissue culture could be an effective way to create clones of hydrangea similarly to cuttings.
Conclusion
The hydrangea is a beautiful shrub with large flowers perfect for use in floral arrangements. There are numerous ways to propagate hydrangea, and while none of them are wrong the easiest way is through cuttings. Cuttings require less care than layering techniques and allow for more plants to be propagated from one plant. Seeds produce plants with varying characteristics, but cuttings produce clones of the parent plants which ensure the continuation of desired characteristics. Stem cuttings are by far the easiest and most reliable way to propagate hydrangea plants, but all methods will create viable seedlings.
References
Abou Dahab, T. (n.d.). In vitro Propagation of Hydrangea macrophylla Thunb. Retrieved October 8, 2015, from http://www.acgssr.org/BioTechnology/V101January2007/Full_Paper/
Hartmann, H. (2011). Techniques of Propagation by Cuttings. In Hartmann & Kester’s Plant Propagation: Principles and Practices (8th ed.). Upper Saddle River, NJ: Prentice Hall/Pearson.
Hydrangea. (n.d.). Retrieved October 8, 2015, from http://www.bhg.com/gardening/plant-dictionary/shrub/hydrangea/
Manipulating Hydrangea Flower Color – Hydrangea Bouquet. (n.d.). Retrieved October 8, 2015, from http://flowersbulbs.com/ql_hydrangea_color.htm
Propagation of Hydrangeas. (n.d.). Retrieved October 8, 2015. http://hydrangeashydrangeas.com/propagation.html
Propagating Hydrangeas: How To Root Cuttings From Hydrangea. (2009, June 11). Retrieved October 8, 2015. http://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-propagation.htm