Four Star Culture Guide - 2019 - 87

HYDRANGEA MACROPHYLLA
and SERRATA CONTINUED
LIGHT/LIGHTING
During forcing, plants should be given as much light as possible
(up to 7,500 footcandles) unless subject to high temperatures
(>75 F). Once flowers show color, shading the plants to 3,000
footcandles is recommended to prevent sun bleaching or burn
of the flower petals. Plants should be spaced such that they do
not shade each other.
TRIMMING/PINCHING
If the grower chooses to start the crop using 28 count liners the
year prior to finishing, it's recommended that trimming stops
after the first week in August, and at least 8 - 10 weeks of
35 F - 45 F temperatures are maintained during dormancy.
GROWTH REGULATORS
Traditional Hydrangea forcing often requires the use of PGRs
for height control. B-Nine®(daminozide) is typically used at a
rate of 2,500ppm - 5,000ppm. Varieties such as Cityline Paris
and Tiny Tuff Stuff ™ are naturally compact plants and may not
need any PGRs during forcing. Larger cultivars such as Let's
Dance Rhapsody Blue and Starlight will likely require at least
one or two sprays of B-Nine. A spray application of 3,000ppm
should be made to Let's Dance cultivars three weeks after the
start of forcing or after 3 - 5 leaf pairs are visible. Multiple
applications may be needed (10 - 14 days apart), depending on
appearance of the plants and rate of growth. Application rate
can be increased to 5,000 ppm if little or no response is evident
after the first application. All growth regulator sprays should be
stopped before flower buds reach 3/4 inches in diameter (size of
a nickel) or flower size will be reduced.

PEST and DISEASE MANAGEMENT
Aphids and Spider Mites are the most common insect pests on
Hydrangea. Avoid using oil-based or emulsifiable concentrate
(EC) pesticides on Hydrangea, as they may burn the plant.
The most common diseases on Hydrangea during forcing are
Botrytis and Powdery Mildew. For Botrytis control, fungicides
of choice are Chipco®, Daconil® or Medallion®. For control
of Powdery Mildew, Compass®, Heritage® or MilStop® are
recommended. Avoid using M-Pede® on Hydrangea because it
can cause phytotoxicity.
Hydrangea Production Schedule
Date

Action

Time to Flower

Temperature

Week 6

Receive plants or
remove from cold

13 weeks

60 - 65 F Night
70 - 75 F Day

Weeks 7 - 8

Transplant

Week 8

Start fertilizing

60 F Night

Week 9

B-Nine spray
(if needed)

60 F Night

Week 11

B-Nine spray
(if needed)

60 F Night

Week 11

Pea-sized
inflorescence

Week 12

B-Nine spray
(if needed)

Week 13

Nickel-sized
inflorescence

6 weeks

60 F Night

Week 15

Silver dollar-size
inflorescence

4 weeks

60 F Night

Week 16

First color,
Lower temperature

2 ½ weeks

54 F Night
65 F Day

Week 19

Flower

Week 20

Mothers' Day

11 weeks

The rates and chemicals listed are based on our southeast Michigan growing conditions, and are not recommended for nationwide application.
Please adjust the rates and spray applications to your location and facility.

8 weeks

60 F Night

60 F Night
60 F Night

Four Star Culture Guide - 2019

Table of Contents for the Digital Edition of Four Star Culture Guide - 2019