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Grower Tips for Hydrangeas

If you want to grow hydrangeas the Dutch way - here are some grower tips for you:

Growing Hydrangea macrophylla in pots for retail sales

  • Cuttings are grown in 50 cells to be shifted to 8”, and in 18 cells to be shifted to 2-3 gallons in late spring to early summer.
  • Accept liner deliveries in April/May depending on the area of the country.
  • Plant by late spring to early summer to guarantee a strong root system and to avoid crowding, which often leads to mold and mildew.
  • To avoid Pythium, never prune a cutting just before, or just after planting - Pinch 2 x before July 7th - 4-5 weeks after the last pinching spray with Banner at the recommended rate (active ingredient Propiconzale) Banner is a fungicide and is highly effective as a PGR on Hydrangeas. Repeat as needed - By September, plants should have 12-20 branches
  • Buds begin to develop in late summer to early autumn, as soon as average day temps range from 55-60 degrees.
  • Buds remain dormant through the winter and require temps just above freezing (34-36 degrees) to complete vernalization. - 6-8 weeks or 1000 hours of chilling is required. This can be achieved in a temperature-controlled greenhouse. If growing outside in colder climates, vernalization will occur naturally, but protection from fluctuating temperatures in the fall or early spring that could damage the buds is imperative.
  • Although Hydrangeas require med-high light levels, too much direct sun will damage flowers and buds. Continue to provide enough supplemental light throughout the winter months to keep buds healthy and to keep plants from becoming leggy.
  • Monitor water use. Excessive water is one of the easiest ways to adversely affect a crop, often leading to blind stems, bud abortion, and ultimately, Pythium. Drip irrigation is preferred. Keep irrigation zones small to allow custom watering zones, and make sure your pots and the table or ground they sit on have adequate drainage.
  • Pest and disease control: - Hydrangeas can be sensitive to Aphids, Spider Mites, Botyritis, Mildew, and Pythium. Before using any fungicides or pesticides please trial on a small scale, since Hydrangeas have proven to be sensitive to some treatments. An application of Imidacloprid (Merit) in the beginning of the season will help eliminate insect problems, but grower must remain vigilant throughout the growing season to combat insects and disease. (systemic)
  • To avoid fungal problems, keep plants free of all dead foliage on pots, tables, and ground. A preventive fungicide is strongly suggested just before plants begin to actively grow in spring
  • During flowering, the flowers are more sensitive to burning. Provide water on a regular basis
  • Coloring of the flowers: - Changing the color of the flowers from pink to blue depends on the pH of the soil and the concentration of aluminum ions present in the media. The recommended pH for growing Hydrangeas is 5.5 - For blue flowers, the pH should never exceed 5.5. Reducing the pH below 4.8 may result in damaged plants with growth impairment. At a pH over 6.5, iron is no longer available, flowers cannot turn blue, and the foliage often becomes chlorotic, resulting in yellow leaves. White varieties cannot be colored blue. In short, both aluminum potassium sulfate (alum) and aluminum sulfate, are essential tools in manipulating the flower color of mop-head Hydrangeas. In September and November apply 15 grams potassium-aluminum (kali- alum) to a 3-gallon container (or adjust to the rate provided for the size container you are growing in) - Or use aluminum-sulfate at a 17-18% rate (given in liquid form) at the end of September or the beginning of October. At the rate of 6 grams on a 3-gallon container (or adjust to the rate provided for the size container you are growing in) - In March and May reduce the rate of aluminum-sulfate 17-18% to 5 grams per 3 gallon, or apply potassium-aluminum again. A missing, or untimely application of alum often results in muddy blue colors - Be sure to follow the schedule and increase the amount of alum where irrigation water is alkaline (high in calcium) - In some cases, it might be beneficial to use rainwater, or soft water to limit the calcium accumulation in containers