Four Star Culture Guide - 2019 - 94

SPIRAEA
ZONE HARDINESS 4 - 9
NUTRITION
pH: 5.8 - 6.2
EC: (2:1 extraction method) 0.6 - 0.9
Moderate fertilization is recommended. 100ppm - 200ppm N.
Additional iron and manganese may be needed if cholorosis is
observed.
TEMPERATURE for forcing from liners
Forcing/Growing on: 65 F Night - 72 F Day
Holding: 40 F Night - 50 F Day
Once plants reach a saleable size, they can be moved to a frost
protected open environment with good air movement. Crops
will slow down in the heat of the summer.
WATERING
Moderate to moist: Water thoroughly without oversaturating,
and keep moist during all stages of production. Spiraea suffer in
quality when exposed to dry down. Keep watered adequately
during the rooting in stage - especially during hot months.
TIMING
28 Liner to True 1 Gallon: 8 - 10 weeks with one plug per
container. A typical planting date for spring forcing would
be Week 10 for finishing in Weeks 18 - 20. If a larger size is
desired, we recommend planting these in the fall and doing
additional bulking prior to dormancy. Planting a 28 count liner
into a 2 - 3 Gallon container and bulking in the summer is also
a great way to finish a larger high-quality spring crop. Double
Play® Gold may require two extra weeks of production time
when planted from all sizes.
Quick Turn™ Liner to True 1 Gallon: 7 - 8 weeks with one
plug per container. A typical planting date for spring forcing
would be Week 10 for finishing in Week 18. Planting a Quick
Turn liner in Week 20 for finishing in Week 28 is also achievable.
Quick Turn Liner to 2 - 3 Gallon: Planting a Quick Turn liner
into a 2 - 3 Gallon container and bulking in the summer is also a
great way to finish a larger high-quality spring crop.

VERNALIZATION
Vernalization for flowering is beneficial on Spiraea. They will
not put on a full flower show without a cold treatment. For this
reason, we recommend planting the previous season for a higher
quality spring display. Care should be taken not to dry down
plants at any point in the production cycle, even in cold storage.
Spiraea can be held with minimal heat throughout the winter.
PLANTING
Spiraea perform best when planted in a well-drained, porous
growing medium. But at the same time, they must always be
kept moist.
When growing shrubs, we recommend using an aged or
composted pine bark-based media, as opposed to an annual
growing mix that traditionally tend to be heavier in peat. Bark
adds weight and stability to the growing mix and tends not to
compress and shrink over time, thus adding the longevity that
can be needed on long-term crops such as shrubs.
LIGHT/LIGHTING
During early spring forcing, plants should be given high light.
Crops should also be spaced in such a way that they do not
shade each other. Unspaced plants can stretch, require additional
pruning, and lead to an undesirable look on the retail bench.
TRIMMING/PINCHING
Spiraea benefit from frequent light pruning rather than hard
pruning. Avoid pruning except for shape in the early spring.
Once the plants have flowered, additional pruning for shape
can resume. They will re-bloom if sheared after the first flush
of color.
GROWTH REGULATORS
Pruning and trimming for shape is used mostly on Spiraea to
control plant height after flowering. Cultural practices such
as cooler holding temperatures, proper spacing and good air
movement in an open environment can also help control plant
height and assist in finishing a high-quality crop.

Four Star Greenhouse I www.pwfourstar.com I 734-654-6420
94

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.

http://www.pwfourstar.com

Four Star Culture Guide - 2019

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