Updated: Dec 30, 2020
Hydrangeas white, blue, or pink? There are many hydrangeas available at the nursery today. The blue and pink ones are the most striking. These are in a group called big leaf hydrangeas (Hydrangea macrophylla). Perhaps you bought a pink one last year, but this year it is blue? The bigleaf hydrangeas can change color depending on aluminum available in the soil. An acid soil will make more aluminum available to the plant and result in a blue blossom. The same plant in a less acid, more alkaline, soil will produce the pink flower.
Big leaf (above)
The hydrangea ‘fertilizer’ you purchase is not really a fertilizer, it is an acidifier. When the soil is more acidic, the aluminum present in the soil is more available to the plant. Hence you get blue flowers on the Bigleaf hydrangeas. Not so for other hydrangeas.
This is not true for other hydrangeas, such as, smooth hydrangea and oakleaf hydrangeas. These two are native plants and do not change color with the acidity of the soil. Their flowers are white, always.
Oak leaf (above)
Do a little homework on the hydrangea you have before attempting to control the color. There are many new hybrids on the market that can make it even more confusing. Have a conversation with a knowledgeable nurseryman before purchasing a new hydrangea.
Should I prune my hydrangea? The different hydrangea species require different methods of pruning. The Bigleaf hydrangeas form flower buds in the fall. These shrubs should be pruned right after flowering. (The old flowers can easily be dried, by cutting the bloom with a stem, and hanging upside down in a dark warm place.) Do not prune in fall, or you may remove the flower buds for next year.
Oakleaf hydrangea can also be pruned right after blossoming. Its flower buds are formed in fall and winter.
The Smooth hydrangea form flowers on new wood. So, the time that you prune is not as important. You may choose to prune after flowering and dry some of the blooms. You may choose to cut the entire shrub in the fall or late winter. New growth will come up from the crown and still blossom. A cultivar named ‘Annabelle’ is readily available at nurseries.
Smooth Hydrangea (above)
Other hydrangeas: Another hydrangea which was very popular in the past is the PeeGee hydrangea (Hydrangea paniculata ‘Grandiflora’). It grows as a large shrub and may be trained to a small tree. The summer flower clusters are very large. A cultivar H.p.’Tardiva’ has recently come into favor; it flowers in September. The cultivar ‘Little Lime’ sports light green to white flowers.
Hydrangea anomala is a clinging vine which has white lacecap blooms in summer. There are so many hydrangea varieties available, a fun group to explore.