Maximum Yield Australia/New Zealand March/April 2019 | Page 42

“There are even some types of grafted trees with two
or three different types of citrus grafted onto the one root
stock, making more efficient use of valuable growing space.”
For hydroponic production, suitable varieties of common
citrus types include Meyer and Yen Ben lemons, Tahiti, Key
and Mexican limes, mandarins, and sweet Washington navel
oranges. Makrut lime is another small citrus tree ideally
suited for indoor hydroponic production which produces a
double crop of highly fragrant leaves which are finely sliced
and used in Thai and other Asian dishes as well as small,
knobbly green fruit which provide aromatic zest and juice. The
advantage of Makrut lime is not only that the fresh leaves are
far superior to the dried version, but the plant is often only
grown for its valuable foliage and doesn’t necessarily need to
flower and set fruit.
Start with Plants from a Good Nursery
For a new hydroponic planting, obtaining relatively young
plants from a reputable nursery is a good place to start as
these can then be regularly pruned to maintain a compact and
attractive shape before flower buds start to form. Obtaining
older, tall and sometimes straggly plants makes the process
of height control much more difficult and productivity often
suffers with this type of planting stock. Once plants are in
place and well established, citrus should be pruned to remove
the growing points of any dominant stems and promote the
production of several side branches which will allow the plant
to carry more fruit and remain compact.
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Maximum Yield
Left: Young fruitlets need high levels of potassium under hydroponic
production. Middle: The uniquely shaped `double’ leaves of the Makrut
lime are used in Asian dishes. Top: Citrus flowers are attractive and highly
fragrant. Bottom: The knobbly fruit of the Makrut lime.
Light, Nutrients, and Pots
Citrus, being fruiting plants, require a moderately high level
of light to keep plants compact, prevent elongated growth, and
produce sufficient assimilate (sugars) for high-quality fruit.
A light level similar to that provided for fruiting tomato and
capsicum plants is ideal, provided citrus trees are not over-
crowded and kept pruned for maximum light interception. If
light levels are low, citrus trees will continue to grow foliage,
but often fail to flower or any sparse flowers that do open may
not carry fruitlets through to maturity. Temperature optimums
are also similar to many other hydroponic fruiting crops,
although they vary depending on the type of citrus being
grown. For optimal year-round growth, most citrus grows well
within a temperature range of 24-30°C, however, will survive
much cooler conditions down to 2°C for short periods of time.
Since most citrus fruits are a long-term crop and will
continue to be productive for many years, growing containers
of at least four gallons are recommended. Substrates such
as coconut fibre or perlite are ideal, however, citrus have
been grown on a wide range of soilless mediums including
gravel, grow rocks, peat, bark, stonewool, rice hull, and
even in aeroponics. Good drainage is essential with citrus
as oversaturated root zones can be prone to root rot, so the
addition of some coarser material in the base of the growing
container is always a good idea for long-term plants.
Drip irrigation systems are most often utilised for nutrient
delivery with standard vegetative and fruiting formulation
applied during the different stages of citrus tree growth.
A nutrient formation high in potassium with additional
magnesium is essential during the fruit formation phase,
as citrus fruit quality is related to potassium nutrition as
well as environmental growing conditions.