A Note On Germinating Macadamia Seeds

A NOTE ON GERMINATING MACADAMIA SEEDS

 

W.B. Storey

 

Reprint From CMS 1980

Even though several articles have been published in previous volumes of the Yearbook on storage and germination of Macadamia seeds, frequently recurring inquiries are "What is the best method for germinating Macadamia seeds?" and "Does placement of the seed make any difference?"

 

My answer to the first question is: I find a medium grade of horticultural vermiculite (zonolite or terralite) to be satisfactory material in which to germinate Macadamia seeds. Some persons prefer pearlite or a mixture of pearlite and sphagnum peat soil. The advantage of these media is that their porous particles are penetrated by the rootlets of the germinating seed. When the seedling is lifted for transplanting, the root system and the medium come out en masse with the root system virtually intact (Fig. 1) in contrast with seedlings started in sand or soil, which may be bare rooted by the medium falling off.

Seeds freshly fallen from the tree may be planted for germination without any pre- treatment. Seeds that have been stored for appreciable lengths of time, especially those in which the kernels have come loose and rattle, germinate more rapidly and uniformly if soaked in water for 48-72 hours. I like to plant the seeds in large pots or boxes not less than 12 inches deep to allow for extension of the seedlings’ taproots.

Fig. 1. Macadamia seedling germinated in vermiculite.

 

If possible the pots or boxes containing the seeds should be kept in a warm place at temperatures above 75 F. until germination is complete. In large operations, seedbeds are kept warm by bottom heat cables.

Janice M. Pyre, R.A. Hamilton and R.T. Sakuoka report some of the factors affecting the germination of fresh and stored seeds elsewhere in this volume of the Yearbook.

 

The answer to the second question is: yes, orientation does make a difference. The seed should be set on its side. However, it does not seem to make much difference whether the ventral suture is up, on the side or down. When germination begins, the cotyledons expand and their petioles extend somewhat. Expansion of the cotyledons usually results in splitting of the shell into 2 near-perfect halves. Extension of the petioles pushes the axis of the embryo out at the micropylar end. The axis consists of a plumule, which develops into the shoot, and a radicle, which develops into the main root. The main root develops first, and after attaining a depth of 3-4 inches, sends out lateral roots. At this time, the shoot begins to develop.

 

Seeds placed in this way germinate into nice straight seedlings (Fig. 2) Seeds placed with the micropylar end up or down often are likely to give rise to seedlings, which are crooked or bent way out of line in the transition region between shoot and root.

 

Fig. 2. Macadamia seedling germinated with the seed on its side. Most of the medium was washed away

to show the connection between the plant axis and the cotyledons still in the shell.

Fig.3

For best placement in the germination bed, place the seed as it is shown in Fig.3. Nomenclature of the seed is, germination seam is the ventral suture. Nutrient connection to inside of husk and seed stem on left side is the hilum. The opposite end is the raphe.This article has been amended by Tom Cooper on February 10,1994 .