Is the color of every type of Hydrangea variable, according to the pH of garden soil? Or are some species or varieties reliably the same color, no matter where they are planted?
I think the main species of Hydrangea whose color gardeners sometimes try to alter is Hydrangea macrophylla, also known as hortensia, bigleaf, or mophead hydrangea. According to Van Gelderen’s Encyclopedia of Hydrangeas (Timber Press, 2004), most cultivars of Hydrangea macrophylla are naturally pink, even in slightly acidic soil. “The key factor in flower color is not the acidity of the soil, but a plant’s accessibility to aluminum sulfate.” The plant will not produce blue flowers if it has access to aluminum sulfate but the soil is strongly alkaline, as the calcium of high pH soils will bind with it, preventing the plant from absorbing it. The authors state that “some cultivars easily turn blue under the right conditions,” while others do not. White-flowered cultivars of different Hydrangea species usually retain their color, though the flowers may become flecked with red or pink toward the end of the season.
Hydrangeas: A Gardener’s Guide, by Toni Lawson-Hall and Brian Rothera (Timber Press, 1995) says that while several species of Hydrangea may have some variation in color, Hydrangea macrophylla ssp. macrophylla and its cultivars (including mopheads and some of the lacecaps) have potential for the most dramatic changes. However, “there are some innate preferences within the individual plants […] and not every mophead or lacecap will change colour in response to a gardener’s alchemy.” The authors do mention a few plants which display red flowers even in acid soil, such as cultivars of Hydrangea serrata: ‘Preziosa,”Grayswood,’ and ‘Beni-Gaku.’ Among the H. macrophylla cultivars that stay red in acid soil are: ‘Alpengluhen,’ and ‘Altona.’ Cultivars which are considered most reliably blue on acid soil also need a low level of phosphate: H. macrophylla ssp. macrophylla ‘Gentian Dome’ and ‘Marechal Foch’ (both deep blue), ‘General Vicomtesse de Vibraye’ (pale blue), and Hydrangea serrata ‘Diadem’ and ‘Blue Deckle’ (blue lacecaps).
I have had a climbing hydrangea for 4 years – but it has never bloomed. It is growing but does not produce any buds. It gets full sun and is in good soil. What can I do so it will produce blossoms?
I looked in a few books (including Trees and Shrubs for Pacific Northwest Gardens, 1990, by Grant and Grant) about climbing Hydrangea (Hydrangea anomala ssp. petiolaris) and they all said this vine is wonderful and robust but very slow to establish. You may just have to wait a few more years.
This hydrangea prefers a cool, moist root run so be sure to irrigate it in the summer and place a good mulch (such as compost or wood chips) a few inches deep. The mulch should not touch the trunk of the vine at the top of the soil around the vine. Established trees and shrubs don’t generally need feeding. Avoid using a fertilizer that is high in nitrogen, or it may add lush, green growth at the expense of flowers.
Here is additional information, from Virginia Cooperative Extension:
Excerpts:
“Climbing hydrangeas only bloom on vertical stems so vines growing on
the ground will not bloom. Minimal pruning is required. They bear lacecap inflorescences with an outer ring
of showy white sterile florets around creamy to yellow fertile flowers in late spring. Deadheading can be
done right after flowering to save energy and for aesthetics by cutting the inflorescences off above the first
leaf. Branches that extend out far from the climbing surface may also be pruned back in summer after
flowering to prevent the plants from being pulled from their structures by heavy winds, ice or snow.”
Reasons for lack of flowers on various species of Hydrangea:
- Improper shearing and renewal pruning on H. macrophylla and serrata cultivars
- Frost injury to early expanding growth buds
- Pruning more than a month after bloom time in summer
- Excessive shade
- Excess nitrogen fertilization
I am attempting to find detailed plant information on a variety of hydrangea called Hydrangea macrophylla ‘Miss Belgium’, and can find very little in my plant books and online. Do you have any suggestions? Some of the details I am looking for are flower shape and size, plant habit, height & spread, and foliage details.
I found some information about Hydrangea macrophylla ‘Miss Belgium’ in Glyn Church’s book, Hydrangeas (Cassell, 1999):
An excellent pink in alkaline soil or in containers. The plant is ideally suited to pot and tub culture as it stays small and compact (3 ft.) and the rounded heads tend to be tiny, keeping the flowers in proportion to the bush. Its free-flowering habit and healthy nature are its good qualities. It is not the best plant for acid soils as the flowers will be a strident purple-blue.
There is a photograph of ‘Miss Belgium’ in Corinne Mallet’s Hydrangeas: Species and Cultivars (vol .1).
Heritage Hydrangeas’ website (no longer available) has this description: “Bright magenta-red on neutral soils or purplish blue on acidic soils, the centre of each floret is always white. Impressive flowers on a compact shrub.”