Eucalyptus seed germination

Most Eucalyptus are propagated by seed - cuttings are possible (but generally difficult) and grafting is even more difficult. 

Seed germination of Eucalyptus generally falls within two categories: Those that need no pre-treatment and those that need chilling or cold stratification.  Only those species that come from colder areas need the cold stratification process.  Seed sourced from warmer climate areas do not need to be pre-chilled.

About 95% of Eucalyptus seed needs no pre-treatment.  Species of the "snow gum" and a few other species found in colder areas provide a better germination rate when they have been cold stratified.  Those Eucalyptus species we have found to respond to cold stratification are:

Amygdalina, coccifera, dalrympleana, debeuzevillei, delegatensis, dives, elata, fastigata, glaucescens, goniocalyx, kybeanensis, mitchellana, niphophila, nitens, pauciflora, perriniana, regnans, stellulata.

Cold stratification of seed is a simple process.  Using a filler like perlite, vermiculite or sand, take 2-3 times the volume of filler per volume of seed.  If you are stratifying 1 teaspoon of seed, use 2-3 teaspoons of filler.  Mix together and slightly dampen and place in a zip lock bag or 35 mm film canister and label the contents and date.  Place this in the refrigerated section of your refrigerator - not your freezer!  Generally 4-6 weeks of chilling is sufficient, although we have not shown any detriment to the seed by leaving it in for longer periods.

After the stratification process is complete you can sow the seed at your convenience.  Don't try to separate the seed from the inert material, sow all together.

Instructions for seed sowing: Eucalyptus seed is generally sold with chaff (inert material).  Sow both seed and chaff on the surface of a pre-moistened media.  Commercial seed starting mixes are available, but I prefer to mix my own using a 3:1 ratio of perlite to sand.  I add a bit of starter fertilizer in with the mix, although the commercial mixes generally have this incorporated into their product. 

In my experience, I prefer to use my own mix as I like a very well-drained media for germination.  Peat based products can "crust over" if too dry or get algae growth if kept too wet.

I sow the seed (and chaff if so mixed) on the surface of my pre-moistened perlite/sand mix.  I cover the seed no more than 1/16" with sand and place the pot into the germination chamber.  Ideal germination conditions are around 68-72 degrees F with a humidity of near 100%.  Even in my enclosed seed chamber, relative humidity rarely exceeds 70% and still we generally obtain good results.  Average germination time is about 2 weeks, although some species will germinate faster and others at a much slower rate.

Once germination has taken place, ideally, you should remove the container of seedlings and place it an an area of bright light and provide a lower temperature of 55-60 degrees F for several weeks.  The lower temperature provides a stockier seedling.  Higher temperatures tend to make seedlings stretch and they become weak and spindly.

Ideally, pick out the seedlings at the "true-leaf" stage for transplant.  The "true-leaf" stage is not the same as the cotyledon leaves.  When a seed germinates, generally 2 leaves will show - these are the cotyledon leaves.  Additional growing time is needed for the "true-leaves" to form.

Once the seedlings are at the "true-leaf" stage, carefully pick out the seedlings and transplant into individual cells.  Hold the seedlings by the leaves, not the stem to prevent damage to the main stem.  Carefully water the seedlings in and monitor media moisture.  You don't want them soggy wet nor too dry, a slightly moist balance is what the seedlings need.

Eucalyptus archerii seedlings at cotyledon stage "True-leaf" development.  Look closely for the second set of leaves forming on the Corymbia ptychocarpa.  

Simple home made propagation/light chamber (click picture to enlarge)

  Pic 1 Pic 2 Pic 3
Pic 4    

In Pic 1 above, I built a simple rectangular frame with lumber to the size I wanted.  I stapled some foam insulation inside the frame to the sides, back and bottom.  The top was left open as well as the front.  I covered the top and front with clear plastic.  This allows the sunlight to reach the seedlings, yet I can easily flip up the front for ventilation or to add/remove seedlings as seen in Pic 2.

I also added a bottom heat mat to provide supplemental heat if needed (Pic 3 & 4).  The mat has a adjustable thermostat to control the bottom heat.  A probe is inserted into the media which signals when the heat mat should turn on or off.  I added 4 grow lights on the left side and 2-4' fluorescent lights on the right.  The heat given off by the fluorescent lights provides enough energy to keep those seedlings not on the mat at a comfortable temperature.

A simple 24 hour timer is used to control the light cycle.  We do a lot of seedling germination during the winter months when the sunlight is less.  The lights add additional "day length" to the production cycle and promotes a stockier plug.  Another benefit is the slight heat given off by the lights to protect the tiny seedlings during the cold winter nights.  (Be sure not to connect the heat mat in with the light timer.  The heat mat controls the heat, the light timer controls the amount of daylight the seedlings get.)

If you use a system like this, be sure to closely monitor the heat inside the light chamber.  On sunny winter days, you may need to open the plastic up to allow trapped heat to escape.  You don't want high temperatures at this time as this causes the seedlings to cook or stretch.  I prefer to keep the system around 55-60 degrees F for proper seedling development.

Fertilizer and fungicides: Do's and Don'ts

Some people use a preventive drench of fungicide when sowing seed and another drench after seedling germination.  While this certainly can be helpful, it is not something the must be done.  There are many commercial fungicides available or you can use alternative products.  Some swear by briefly soaking seed in hydrogen peroxide

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Sunday August 28, 2011 12:52 PM