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What’s the problem?
In warmer areas of New Zealand, many tulip cultivars may need
refrigeration before planting.
You probably need to consider refrigeration if your
flowers have unusually short stems or
your bulbs occasionally fail to
flower altogether.
Why does it
occur?
Tulips are native to areas which experience quite cold winters, and
they need this cold period for the bulb to complete the development of
the flower bud deep inside. Insufficient
cold period results in either no flower or flowers on short stems.
Does it
affect all tulip types?
Darwin Hybrid tulips and Species tulips are the most suitable types
for warmer areas. If you
want to grow all the colours available in the Single tulip range or have
the pleasure of growing types from the exotic Parrot tulips to the
graceful Lily types, then you will need to go to a little more trouble.
Are there
any alternatives to chilling?
A number of things may help you get good tulip flowers without
chilling:
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All tulips should be planted later in autumn when the soil
temperatures are cooler, ideally below 12ºC. Mid to late May is an ideal time.
-
Plant the bulbs 20 cm deep as the soil is cooler at that
depth. The bulbs cope very
well as long as the soil has been well worked down to 35 cm or more to
allow a good root run.
-
Use a mulch to help keep the soil cooler.
How do
I go about chilling?
The most important point is that you need to chill, not freeze!
Don’t put bulbs in the freezer as this is too cold and will
kill them. The average
fridge is at approximately 4ºC and this is an ideal temperature.
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Place the
bulbs in a breathable container such as a paper bag and start chilling
before the end of March. Continue
for at least eight weeks before planting in May.
Are there any problems to watch out for?
Done correctly, chilling your tulips
will result in perfect flowers next spring.
However, if it is not done well, keeping bulbs in the fridge can
cause as many problems as it solves.
-
Using a paper bag is very important so the bulbs can
breathe. Plastic bags cause
sweating and rot may develop.
-
Keep the bulbs to the side of the fridge, not at the back
where the cooler plate may ice up and damage them, or condensation may
cause mould to develop.
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Ripening fruit releases a gas called ethylene.
This gas causes other fruit to ripen in a chain reaction.
We make use of this sometimes by getting kiwifruit to ripen more
quickly by putting them in a bag with apples or bananas, which are
higher ethylene producers. However,
ethylene causes severe damage to the developing flower bud in the bulb,
often resulting in complete loss of the flower.
Including an ethylene-absorbing sachet in the bags with the bulbs
will prevent ethylene damage and supress mould growth.
Ethylene-absorbing sachets are low cost
and make flower bulb chilling a safe option.
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