Are you thinking of adding a Hydrangea ‘Nikko Blue’ to your garden landscape this season? There are many qualities that make this particular hydrangea variety a popular choice amongst gardeners. In this article, gardening expert and hydrangea enthusiast Jill Drago shares everything you need to know about this type of hydrangea, including maintenance and care.
I. Appearance and Characteristics
The Nikko blue hydrangea is a bigleaf hydrangea cultivar part of the Hydrangea macrophylla genus. Many people call them the mophead hydrangeas as they have oversized blooms. The foliage is thick, adding loads of greenery to foundation plantings.
Still, of all the species, this one is the least resistant to cold to grow in zones 6-9. It is a deciduous shrub that can reach heights of 4 feet tall and 4 feet wide, and even higher. The shrub blooms rounded flower heads.
While the flower color is typically blue, it is not always the case, as the color changes depending on the soil’s pH. Yet, most of the time, it has a sky-blue color. But when the soil pH moves to the alkaline side, you get purple to pink flowers.
The Nikko blue hydrangea blooms in early summer and continues with healthy buds growing for up to two months. The shrub produces new flowers throughout the summer. Thus it makes for a beautiful accent plant.
So, you can choose the soil type you want, from acidic to alkaline soils, to determine your plants’ color.
II. How to Grow and Care
Sunlight
While the Nikko blue hydrangea can tolerate direct sunlight in the morning, providing it with afternoon or part shade is best. If you live in the South, we recommend more shade. While living in cooler climates, full sun is best. The important thing is to provide your Nikko Blue with eight hours of sunlight.
Temperature and Humidity
Hydrangea macrophylla can grow in different climates, and you can even overwinter them in some regions. A mature plant can tolerate temperatures down to 30°F, but your younger plants must be kept above this range
Blue hydrangeas like high humidity and can thrive in moist heat during summer. But when the air becomes dry, the leaves start to sag. Another important thing is to provide your outdoor plant with air circulation to prevent diseases.
Watering
Water them several times weekly when young plants still try to become established. It will help them establish a robust root system. Mature plants can tolerate some drought and receive water from rainfall.
But if you have dry spells, we recommend providing them with one inch of water per week. Also, water your Nikko blue hydrangeas at the base and avoid overhead watering, which can lead to fungal infections.
Soil
For Nikko blue hydrangeas to grow best they need well-draining soil canty to hold on to a bit of moisture. If you have soil that tends to pool or dry out too quickly you may need to amend your garden soil with some compost or other organic material.
Hydrangeas also prefer slightly acidic soil. You can find out the acidity of your garden soil by having a soil test done.
This will give you the soil’s pH and other information about the nutrient that naturally exist in your garden. Acidic soil has a pH of 6.5 or less. If your pH is higher than that your hydrangea will still grow nicely but amending it will allow the shrub to thrive.
Fertilizing
Nikko blue hydrangeas do not necessarily need fertilizer. Depending on the results of your soil test, you may be able to skip this step. However, you may choose to fertilize your hydrangeas in the spring which can be beneficial.
If you choose to fertilize your shrubs a second time keep in mind that this second fertilizer application needs to be done before the end of September. This will prevent the hydrangeas from producing any new growth too late in the season which could be damaged by frost and other winter weather.
You can use an all-purpose fertilizer, such as a 10-10-10 on your hydrangeas. If you are looking to boost your blooms you may opt for a fertilizer with a higher middle number. This number represents phosphorus which is key for flowering.
If you would rather stay away from traditional fertilizers adding compost to your garden beds is a great way to naturally add nutrients to your gardens resulting in healthy and happy plants.
Planting Instructions
Just as caring for ‘Nikko blue’ is simple, so is planting the shrubs themselves. Once you have brought your hydrangeas home from the garden center arrange the potted hydrangea where you think you want to plant it.
Take a few steps back, and make sure you are leaving enough space between plantings so that everyone will thrive. Once you are confident in your placing, dig a hole about two times as wide and deep as the root ball of the hydrangea.
Gently place the hydrangea in the hole and spin it around so the best side of the plant is facing outward. Backfill with your garden soil, and water thoroughly.
You will want to check the moisture level of the soil daily for a few weeks, especially during any hot stretches. This will help prevent any transplant shock which can lead to the loss of the hydrangea.
Pruning
When you need to prune your Nikko Blue, an important thing to remember is that compared to other plants; it blooms on old wood. Hence it will bloom on the previous year’s growth.
So the best time to prune is in summer after the flowering period ends. Then, you can cut back the stems to healthy buds or prune out winter-damaged stems in early spring.
Furthermore, not losing any flowers the next year helps to prune in early fall before new buds form. Dead branches you can remove at any time.
Propagation
The most successful way to propagate ‘Nikko blue’ hydrangeas is by taking softwood cuttings or by ground layering right in your garden.
Softwood cuttings should be taken in late spring to early summer. Select a 6-12 inch section of fresh green growth that has at least a few sets of leaves on it.
Dip the end of the cutting into some rooting hormone powder and stick the cutting into some sterile planting soil. Once the cutting has formed roots you can plant it in your garden, or you can continue to transplant it into larger pots until the hydrangea has grown a bit.
Garden layering is a very simple and fun way to propagate new hydrangeas. Select a low-growing branch and remove some of the bark and leaves.
Dig a shallow hole and place the branch in the hole, keeping it weighed down by a stone or brick.
Cover the branch with soil. Roots will form from the exposed growth points, at this point you can cut the branch from the mother plant and transplant this new hydrangea to another area of your garden.
Pests and Diseases
The Nikko blue hydrangea encounters many common pests and diseases. One plant disease is botrytis blight. These fungal diseases kill the buds before it opens, also known as bud blight.
Another concern is leaf spots showing up as brown or purple on the foliage. It can result from excess water done with overhead watering and not at the base of the plant. To prevent this, increase air circulation allowing the leaves to dry.
Other plant diseases are powdery mildew and bacterial wilt affecting this deciduous shrub. Pests that eat holes in the foliage are aphids. You can treat the infestation with neem oil or a mild insecticide.
III. Uses and Benefits
Nikko Blue Hydrangea is perfect from foundation plantings to container plantings. Massed in a sheltered location or as an accent plant. Effective as a hedge and makes excellent cut flowers too!
