Why do my Hydrangea fail to bloom?
I got out of the stores last week and got to go to the Dentist! I know that doesn’t sound like a great afternoon off for most of you, but in last weeks extended heat wave, going anywhere with air conditioning was like a mini vacation! While having my teeth cleaning the hygienist had lots of questions about her garden. I love plants and am always happy to talk about them, including waiting in line at the check out at the grocery store, having a meal out at a local restaurant and indeed even when having my teeth cleaned! It’s not just me, Alec, Rick and Angela have the same experiences and we often get an opportunity to laugh about our out of work – work experiences. You know you’ve been doing the same job for a long time when random people at the grocery store ask you questions about their petunias!
The single most popular question we get asked (both in and out of work) is “Why don’t my Hydrangea flower?” I’ve written about and talked about Hydrangea more than most other flowering plants combined. This week’s advice is a rerun of advice I gave last year on this blog – I’m not out of gardening advice yet, but this questions comes up so often that I’m hoping you’ll forgive the rerun!
All through late summer and early fall we hear from customers who are having difficulty getting their Hydrangea macrophylla (Big Leaf or Mop Head) to bloom. We often hear that their Hydrangeas have great foliage, but no flowers in sight. It’s hard to not be impressed with Hydrangea flowers and to want them in abundance in our yards. Understanding the different varieties of Hydrangeas and their specific needs is the best way to ensure lots of flowers.
Hydrangeas are among the most popular plants we sell. In a landscape or garden they produce an abundance of long lasting summer flowers. Hydrangeas come in white, pink, purple and blue. A long time favorite of local gardeners is Nikko Blue, a large leaf variety with big blue flowers. Nikkos used to be the standard tried and true variety for New England. Their challenge however, was that they did not reliably bloom because the cold winters killed the stems and the flower buds down to the ground. Winter damaged plants usually came up in the spring from the ground with beautiful leaves, but no flowers.
The easiest way to help protect the flower buds of your Nikko type hydrangea is to mulch it in like you would a rose bush. A weed-free mulching hay is the best type of mulch to use, but bark mulches like pine and hemlock will also do the trick. The quickest way to get the job done is to buy a Rose Cone, a pyramid shaped device with an open top, place it over the Hydrangea bush and fill the cone with weed-free mulching hay. I usually wait until we’ve had several hard frosts to knock most of the foliage off the plant, but do it before the ground has frozen solid. Instead of purchasing a Rose Cone, you could make a similar device out of chicken wire or wood. It’s important to leave the top open so air and moisture can still get in and circulate. The Rose Cone and mulch needs to be removed in early spring.
Another reason your Hydrangea fail to bloom is bad pruning practices. My grandmother’s rule of thumb for pruning Hydrangea was simple and worked every year. She never touched them until after Mother’s Day. Most older varieties of mophead and lacecap Hydrangeas flower off of old wood. This means the flowers buds for next year will be produced and wintered over on the stems from this year. If this year’s stems are cut back in the fall or early spring, you’ll be cutting back your chances of seeing flowers. This doesn’t mean you can’t clean up your Hydrangea in late spring by pruning out any stems that didn’t leaf out all the way. The exception to this no pruning rule are panicle type Hydrangeas like PeeGee, Limelight and Quick Fire. These Hydrangea paniculata need to be pruned in early spring to control their size and give them a better shape.
For the past 10 years most hydrangeas we’ve sold have been of the “Endless” varieties. From the original Endless Summer, the category of repeat blooming hydrangeas has grown dramatically. The difference between a reblooming variety and a Nikko types is that the new cultivars produce new flower buds during the growing season – so they boom from July to frost!
These new varieties like to be pruned lightly in the spring to control height and spread. If you prune the faded flowers during the summer, new flowers will quickly form.
Improper fertilizing of Hydrangeas can also be another reason for poor flowering. Hydrangeas can be sensitive to over fertilizing with high nitrogen levels. If you use a liquid fertilizer in your perennial beds and your Hydrangea gets a dose of nitrogen every week, you very well may see huge, healthy foliage with little to no flowers. Sometimes over-fertilizing Hydrangeas is a by-product of their being close to a lawn that gets fertilized frequently. Most turf fertilizers are high in nitrogen and some leaching and spreading away form the lawn and into landscapes can occur.
Hydrangea perform best when provided with a spring and late summer application of a natural, granular fertilizer like Espoma’s Holly Tone. The spring application gets them off to a good, healthy start and the late summer application provides nutrients when the plant is setting its flower buds for next year.
Flower colors can vary considerably on the same species of Hydrangea. These “mop head” type hydrangea are the ONLY hydrangea whose flower color can be altered by controlling soil acidity. Most blue flowering varieties like Nikko and Endless Summer will produce shades of blues and purples depending on how acidic your soils are. To deepen the blue coloring you’ll need to acidify your soils by adding some Garden Sulfur. Our soils here in Central Massachusetts tend to be acidic, so we get blue flowers without much effort, but if you want a really dark blue Hydrangea like you see on the Cape, you’ll need to add Garden Sulfur to your soils every Spring. An all purpose fertilizer like MirAcid will maintain soil acidity, but will not change the color of your Hydrangea. Alkaline or sweet soils produce pink color blossoms. To turn your Hydrangeas more pink, add lime to your soils. These techniques for color variations work gradually. Lime can take months to work into the soil.
Sunlight can also play a factor in how well a Hydrangea blooms. I’ve seen beautiful Hydrangeas in full sun and also in very shady areas. They perform best in morning sun with some afternoon shade. If your Hydrangea is in dense shade, you may want to think about moving it to a more sunny location.
Because hydrangeas have big leaves, they use a lot of water. They can wilt easily on hot sunny days. Mulching around the plant with 2 to 3 inches of bark will help to retain soil moisture and help keep the roots cool.
Hydrangeas do best in well drained soils with organic matter. Adding lots of organic matter like a planting mix, compost or cow manure at the time of planting is the best practice. Although Hydrangeas like well drained soils, they aren’t very drought tolerant. A good watering or heavy rain twice a week during the summer and fall will ensure plenty of healthy blooms for this year and next. Newly planted hydrangea will need to be watered well at least three times a week during the summer for the first two years as these plants are slow to establish in gardens.
If all this sounds like a lot of work to you, you’re in luck! Repeat blooming hydrangeas are abundant here at our stores. These new varieties flower on the new growth, so even if the old growth is killed during the winter or you got overzealous while pruning, you’ll still get lots of flowers. I can personally attest to their hardiness and resilience as I have Endless Summer and Penny Mac planted in my front yard here in Lunenburg. Easy to grow with little to no maintenance makes these new Hydrangea varieties a joy to plant!
We are always happy to talk plants – so if you see us out of the stores – say Hello!
Michelle and Team Lakeview!
