Re-Using Tulip Bulbs in Warmer Climates

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Bulb growers in warm climates (e.g. Perth, Brisbane, Sydney) face some difficult issues with respect to re-using tulips for second and subsequent years.

These issues relate to:

1. The short period for new bulb growth following flowering
2. The very long period of senescence
3. Summer heat

1.   The short period for new bulb growth following flowering

Tulips and Dutch iris differ from many bulbs in that the bulbs produced after each growing period are new bulbs.   The bulb that is planted is used up producing the new leaves and flowers and new bulbs that were embryonic in the planted bulb grow to replace the planted bulb.   Normally, 2-3 new bulbs are produced but the total aggregate weight produced is usually no more than double that of the planted bulb.   For refrigerated bulbs, the yield is usually no more than the planted weight – i.e. no increase in weight at all.

The growth of the new bulbs is mostly in the period between flowering and senescence.   To maximise this new bulb growth, the ideal conditions are cool-warm temperatures (say 15-20 degrees C) combined with optimal nutrition and moisture.  In warm climates, refrigerated bulbs often have a relatively short period between flowering and senescence due to a too-warm climate and effects of the refrigeration.   Consequently, many of the bulbs produced will mostly not flower because they are too small.    Tulip varieties have critical bulb circumferences before they will flower.  For many varieties that circumference is about 8 cm but can vary from 6-9 cm for common varieties.

Therefore, problem number 1 for tulip growers in warm climates is that there may well be a shortage of bulbs that are of flowering size following growth.

2.   The very long period of senescence

Dormant tulips are basically an energy store which also contains embryonic leaves, flower and bulbs for the coming crop.  They are still alive and continually use energy and lose moisture.  A commercial tulip grower will normally have the bulbs in storage from say, mid-December until mid-April – say 4 months, maybe 5.   The December harvest will follow planting in mid-April and flowering in early October (the bulbs will not have been refrigerated).  

A gardener in a warm climate would have refrigerated the bulbs and planted them in mid-May.   The bulbs will flower in about late July-August and die back in late September.   The following year they cannot be planted again because of the heat until mid-May.  This is a period of about 8 months.   This is a very long time to have tulips out of the ground and by this time the bulbs will be significantly compromised.

3.   Summer heat

Tulips need a period of about 8 weeks following lifting to develop the flower for the new season.  They do this best a temperatures of about 20 degrees.    Once the new flowers are developed they are susceptible to abortion if they are subject to extended periods of temperature in excess of 30 degrees.   For air conditioned homes this may not constitute a problem but in many situations it does, especially when high daytime temperatures are combined with warm nights as well.

How to Maximise the Chances of Second Crops

The above problems may make it look as if it is too hard and in some situation it probably is.   Certainly, a third crop in warm climates will be extremely difficult.  However, there are ways to maximise chances based on confronting the problems noted above.

1. Variety selection is very important if you want a second crop.   On the other hand, if you wish to grow the tulips as annuals you can use virtually any variety.

Tulips vary in the amount of cold they need to produce good growth.   For warm climates, it makes sense to use the varieties which need the least cold to flower successfully.   These varieties are noted in our catalogue as being suitable for warm climates.  Generally, they are members of the group of tulips known as “single lates”.  

Varieties which need the least cold need the least time in the refrigerator and so will most likely produce the biggest crop of bulbs and also, possibly, die back the latest – thus minimising the time in storage.

1. Storage of the bulbs is also important.   Ideally the bulbs should be at about 20 degrees, well ventilated and free of aphids.   Storage at temperatures around 25 degrees will be ok but a critical point is reached nearing 30 degrees where the new flowers will abort.   The bulbs will then be put in the refrigerator for the desired time before planting when the soil has cooled to about 15 degrees.
2. Planting in optimal conditions also helps – provided viable bulbs with flowers inside them are used.    In warm climates the bulbs are often planted in pots.   Pots have the advantage that they can be moved and placed in total shade in the coolest place in the garden from planting until they emerge (say 5-10 cm high).   Then they can be placed in whatever position is desired.  This is good practice in cool climates as well.

Still too hard?

Comfort yourself with the fact that tulips have never been cheaper and in the last decade the real price has fallen by about 75%.   Perhaps you can now afford this spectacular celebration of spring through annual purchase of the bulbs.   Also, annual purchase allows tulip growing even in hot climates in Australia.

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