Herbertia 1945
Hot Water Treatment for Rejuvenation of Amaryllis Bulbs
Ida Luyten

In my researches on vegetative propagation, I often had small hybrid Amaryllis (syn. Hippeastrum) bulbs (circumference less than 10 cm., and 10-16 cm.) which stayed behind the others. They did not increase in size although for the rest they seemed quite healthy. Mr. Th. M. Hoog, mamber of the firm C. G. van Tubergen, Jr., at Haarlem, advised me in 1927 to try a hot water treatment. As these bulbs were kept growing on in consequence of their small size, Mr. Hoog advised me to give them a bath at the end of December or the beginning of January. He also told me to cut off the roots after the treatment before repotting. This manipulation should further speedy rooting, while the presence of the old roots would give chances for rotting.

We chose 43.5°C for the hot water treatment, the same temperature that was used for combating eelworms in hyacinths and daffodils (van Slogteren 1920):—

To keep the water constantly on 43.5°C, we used our automatic mercury-regulator (for description see Versluys 1927 page 14) which was placed (hung) in the water of a zinc tank with its whole u-shaped part as far as the screw. By means of this screw the regulator can be accurately adjusted to °C; the regulator switches off and on the current for two round-shaped electric-stove elements, placed under the tank. The bulbs are brought into the water in small labelled sacks, using a basin tray with a bottom of gauze. This tray protects the sacks from sinking to the bottom of the tank which is heated directly and therefore has a much higher temperature. The gauze makes possible good circulation of water.

After this treatment the bulbs soon formed roots and leaves. After 1928 the hot water treatment was put into practice every year. We also treated larger bulbs measuring 16-18 cm. Encouraged by the favorable results we later also treated bulbs destined for forcing (circum. 18-20 cm.) or bulbs which were clearly decreasing in size. Depending on the time we started and the storage treatments, the hot water treatments were given in the 2nd and 3rd week of September—in later years always in the first week.

The leaves were cut off but, it was not necessary to remove the roots of the larger bulbs. After the treatment the bulbs were planted at once, and the roots soon formed new laterals.

Some figures showing the effect of the treatments on bulb circumference are given below. It is known, that the hot water treatment has also a good influence on the growth of Hyacinths and Narcissus (van Slogteren 1931). It is interesting to note that Amaryllis bulbs with a relatively smaller bulb circumference flower after the hot water treatment:—No. 20, 78 and 25 have 2 flower-stalks (scapes) with a bulb-size of resp. of 17.0, 16.9 and 17.4 cm.

Table 1.

No. circum.
Sept. '35
cm.		number,
flower
scapes		 circum.
Sept. '36
cm.		number,
flower
scapes		 circum.
Sept. '37
cm.		number,
flower
scapes		 circum.
Sept. '38
cm.		number,
flower
scapes
20 19.40 17.0 (W)2 27.13   
23 21.70 19.0 (W)0 26.42 33.11
78 15.050 16.9 (W)2 22.4    
90    18.6 (W)2 27.5    
92 18.4
17.4		0
0 		18.0 (W)
18.3 (W)		0
0 		30.9
22.15		2
1 		38.15
28.2		2
1
125 15.3 (W)
17.9 (W)
18.7		0
0
0 		23.6
27.1
18.0 (W)		1
3
  		23.5
28.4
18.4 (W)		0
2
  		24.5
27.1
27.2		2
1
2
25 15.3 (W)
17.4 (W)		0
0 		17.4 (W)
16.5 (W)		2
  		22.1
22.1		1
1 		28.85
24.8		1
1

Table 1 shows that without hot water treatment several bulbs kept the same circumference for some years in succession (No. 78, 92, 125, 125) or decreased (No. 20, 23). After the treatment (indicated by W) they increased in thickness, often very rapidly (see for instance nos. 20, 90, 125). These bulbs maintain mostly a good circumference. Sometimes one has to repeat a treatment after several years. Also one hot water treatment may not be sufficient (25 and 125). If one repeats the treatment the following year, the bulbs will surely increase thereafter. Once in a while it occurs that a bulb dies after the treatment. If this happens, it will always be evident by cutting, that the bulb had been disease. This was the cause of the decaying in growth; the hot water treatment made it worse and the death was a result. We can advise this hot water treatment with the utmost confidence. The cultivation of Amaryllis bulbs will be facilitated by it. It will also be possible to rejuvenate rare and expensive bulbs, that are declining, into good large flowering ones again.

November 1945

Laboratorium voor Plantenphysiologisch,
Onderzoek, Wageningen, Holland

Literature Cited