12 



MISCELLANEOUS PUBLICATIONS 1251, U.S. DEPT. OF AGRICULTURE 



CULTURE TECHNIQUES 



Containers 



The plant container must be of sufficient size to 

 permit adequate root growth; otherwise the de- 

 velopment of the plant may be restricted. For 

 example, a pea plant can be grown to maturity in 

 a 10-cm. plastic pot filled with vermiculite or in a 

 500-ml. jar filled with nutrient solution. A corn 

 plant grown in a 10-cm. pot or 500-ml. jar becomes 

 rootbound after 5 to 6 weeks of growth and ab- 

 normalities will occur. Corn plants require an 

 18-cm. pot or 2-liter jar to grow to maturity. For 

 this reason various types and sizes of containers 

 are used, such as jars, stainless-steel troughs with 

 lids, and plastic pots with saucers. Milk cartons 

 can also be used as disposable containers. They 

 will often last for 6 to 8 weeks. Glass jars are 

 covered with a coat of black paint followed by a 

 coat of aluminum paint. The black paint excludes 

 light, inhibits growth of algae in the nutrient solu- 

 tion, and prevents abnormal root pigmentation. 

 Since the aluminum paint reflects sunlight, the 

 jars remain cool. 



When many plants are to be grown together in 

 the same container in nutrient solution for experi- 

 mental purposes, we use a stainless-steel trough, 

 66 by 15 by 10 cm., with a stainless-steel lid (fig. 2). 

 The plants are placed in holes in the lid, which 

 serves as a support and keeps out the light. Soft 

 plastic collars may be used for additional stem 

 support. The size of the holes should be adequate 

 to prevent stem girdling. Alternatively the flat 

 steel trough lids may be replaced by wood or plas- 

 tic frames with nylon screen bottoms. These 

 frames are supported within the troughs, 3.8 cm. 

 above the bottom (fig. 2). The screen is filled with 

 vermiculite. The plants can be grown directly from 

 seed or transplanted. Nutrient solution is added to 

 wet the vermiculite. The plant roots grow through 

 the screen and into the nutrient solution. Many 

 plants grow well in this manner. The screen gives 

 good root support, and most of the roots can be 

 harvested. 



Plexiglas framing is preferred to wood to avoid 

 leaching of chemicals from the frame. If in an ex- 

 periment it is necessary to treat the roots by add- 

 ing a chemical to the nutrient solution, a wooden 

 frame might become contaminated and should be 

 discarded. 



When plants are grown in jars, the jar lids, 

 tinfoil, waxed cork, Masonite, or other materials 

 can be used for plant support. However, we have 

 found paper cups most satisfactory for support. 

 They can be used in different ways depending 

 on the species of plant to be grown. For example, 

 when pea plants are grown, two cups are glued 

 together on the bottom (fig. 4). The lower cup 

 slips over the outside of the jar; the upper cup is 

 used for plant support. One small hole is punched 

 through the bottom of each cup for the seedling 

 and another small hole through the lower cup 

 for the aeration tube. 



Reasons for using this technique are as follows: 

 (1) The cups are chemically unreactive. (2) They 

 are cheap enough to be discarded after a single 

 use. (3) Sharp cutting edges are eliminated that 

 may injure the hypocotyl, stem, or roots. (4) 

 Girdling can be prevented by gradually enlarging 

 the hole as the plant stem increases in diameter. 

 (5) Cups can be easily lifted so that nutrient 

 solution can be added. (6) Plants can be easily 

 transferred to other jars. (7) There is more 

 stem support for certain plants than with many 

 other types of lids. 



Aeration 



When plants are grown directly in liquid cul- 

 ture, air usually must be supplied to the nutrient 

 solution. A small electric pump such as a fish 

 tank aerator can force air through rubber or 

 plastic tubing to the jar or troughs. Glass capillary 

 tubing is inserted in the solution. A well-regulated 

 uniform flow rate can be obtained for several 

 aerators on the same line by inserting a 2.5-cm. 



9&&ty^D 



PN-2926 



Figure 4. — Paper cups and lid supports for plants grown 

 in culture jars. 



