referring now to the drawings , reference numeral 1 indicates one illustrative embodiment of hydroculture planter of the present invention . the planter 1 includes a lightly frustoconical liner 3 filled with growing medium 5 , a light / liquid meter 7 , and an outer pot 9 . a plant 10 in the planter is fed and watered entirely with an aqueous solution of nutrients 12 , in accordance with known hydroculture techniques . the nutrient is preferably a complete nutrient solution that contains no detrimental chemicals , while providing all known elements required for proper plant growth in a form readily useable by the plant . the liner 3 is made of horticulturally neutral , opaque , one - sixteenth inch polyethylene . it has a sloping side wall 11 and a bottom 13 the liner 3 is approximately seven inches high , nine and one - half inches in diameter at its top and eight and three - quarters inches in diameter at its bottom . at its upper , open , edge , the liner 3 includes an offset rim 15 for stiffening the liner . tabs 17 are provided at the top of the rim 15 for lifting the liner 3 from the outer pot 9 . each tab 17 has raised ridges 19 on its upper and lower surfaces , to provide the user with a firm grip on the tabs even when the tabs or the user &# 39 ; s hands are wet . the side wall 11 of the liner 3 includes an arcuate indentation 21 extending from the rim 15 to the bottom 13 of the liner 3 and flaring somewhat toward the bottom . at its upper end , the indentation 21 has a horizontal closure wall 23 with three holes 25 in it , for holding the light / liquid meter 7 as described hereinafter . the closure wall 23 is inside the rim 15 and gives the impression , when the liner 3 is filled with growing medium 5 , that the meter 7 extends into the growing medium . side wall 11 also includes five aeration slots 27 . each aeration slot 27 is four inches long and five - sixteenths inches wide . the slots begin one - half inch from the bottom wall 13 of the liner 3 . the size and position of the slots are carefully chosen , as described hereinafter . a raised center portion 29 of bottom wall 13 is approximately two inches high and five inches in diameter . both the raised center portion 29 and the lower surrounding portion 31 of the bottom wall 13 have drainage holes 33 . the size and number of the drainage holes are not critical to the operation of the system . raised center portion 29 forms a reservoir of liquid so that more liquid may be stored in the system without being displaced by the growing medium 5 . it also defines a platform above the level of liquid in the system for purposes described hereinafter . radial feet 35 on the bottom wall 13 raise the bottom wall three - sixteenths inch above the outer container 9 . the growing medium 5 is therefore held one - quarter inch above the bottom of the outer container 9 , for purposes described hereinafter . the growing medium 5 is expanded slate in the form of oblong pellets having a length of from about ten to twenty millimeters . the slate is expanded in a rolling kiln , to eliminate sharp edges which might cut delicate rootlets . it has been found that horticulturally stable slate is widely available , which does not decompose , rot , or slake in water . slate when fired expands vertically , similar to mica , forming wafer - like layers . these layers with their edge separation provide a much greater surface - area - to - size ratio than any product previously tried . this greater area allows for much better liquid retention and lends excellent anchorage of the root structure to the medium and also allows the substrate to hold and release its water / nutrient mixture and oxygen freely . the size of the material offers excellent plant holding capabilities without compaction during shipping . after a plant 10 has aged in the system , it is not uncommon to be able to invert the pot and remove the plant and its root ball without loss of any medium . the medium 5 has one - third the weight of soil . the light / liquid meter 7 , as described hereinafter , is designed to indicate when no liquid remains in the outer pot 9 , as an indication that an aqueous nutrient solution must be added . it also indicates when liquid has risen to the top of the raised area 29 , as an indication that too much liquid has been added and some should be removed . in the preferred embodiment , it also indicates when the proper amount of liquid has been added . liquid level indicators comprising elongate members in the form of rods of light - transmitting material have heretofore been used for the purpose of indicating the level of liquid in industrial containers pliml , u . s . pat . no . 3 , 535 , 933 , discusses the theory of such meters , and his disclosure is hereby incorporated by reference . the light / liquid meter 7 includes transparent light transmitting rods 41 , 43 , and 45 free from any peripheral interference . these rods are positioned such as to remain physically separated although adjacently positioned . the rods are preferably made from tinted extruded polysulfone . the upper portion of each light transmitting rod 41 , 43 , and 45 is mounted in a single , stepped connecting body 47 . the flat upper surfaces of the light transmitting rods form indicating surfaces 49 which are flush with the steps of the connecting body 47 . the rods extend below the connecting body 47 and terminate in conical tips 51 . the tips 51 have an included angle of ninety degrees , so as to reflect back light to the indicating surfaces 49 when the tip is in air , but so as to refract light out of the rod when the tip is immersed in a liquid having an index of refraction more nearly that of the rod . the rods are of varying length , rod 41 being the shortest and rod 45 the longest . rod 45 extends below the bottom of the liner 3 to the bottom of the outer pot 9 . rod 41 extends to a point slightly below the top of the raised center 29 . center rod 43 extends approximately three - quarters inch below the top of the raised center 29 . the light reflective characteristics of the light / liquid meter 7 are much improved by maintaining the rods &# 39 ; indicating surfaces 49 flush with the top of the connecting body 47 . further enhancement is obtained through the choice of the plastic and through carefully controlled forming methods . the outer pot 9 is made of opaque one - eighth inch polyethylene . it has an inner diameter one - quarter inch larger than the outer diameter of the liner 3 . the exterior base of the container 9 has several little feet or ribs to hold the container bottom away from the surface on which it is placed . these feet are inside the circumference one tenth of the diameter of the container . their purpose is to prevent sweating under the container and damage to furniture . the planter 1 is prepared for use by placing the growing medium 5 in the liner 3 and planting the plant 10 at the proper depth in accordance with known hydroculture techniques . the appropriate light / liquid meter 7 is installed in the liner 3 by sliding the light transmitting rods through holes 25 until the connecting body 47 is flush against closure wall 23 . the plant pot liner 3 complete with medium 5 , meter 7 , and plant 10 is then placed in the outer pot 9 of the system , and the planter 1 is moved to a possible permanent location . enough water or liquid nutrient 12 is added to cover the end of the longest rod 45 . light is refracted from the tip 51 of the rod 45 , and its indicating surface 49 appears dark even in the brightest of ambient light conditions . because the diameters of the rods 41 , 43 , and 45 have been predetermined for the type of plant in question , the viewer merely notes whether the rods &# 39 ; indicating surfaces 49 appear different , indicating proper light location for the plant , or appear the same , indicating not enough light for the plant . it is not necessarily bad for a plant to receive more light than necessary . when a location has been picked for the planter 1 , more aqueous nutrient 12 is poured into the growing medium 5 until the second rod 43 suddenly becomes dark . at that moment , sufficient nutrient has been added . if the third rod 45 becomes dark , too much nutrient has been added , and the excess must be drained , preferably by first lifting the liner 3 out of the outer container 9 , using the tabs 17 . the planter 1 may then be left alone until the longest rod 45 becomes light . the geometry of the liner 3 , the slots 27 , and the raised and lower areas 29 and 31 , as well as the clearance between the inner pot 3 and the outer pot 9 , are all chosen to provide proper watering , feeding , and aeration of the plant 10 through its roots . the raised area 29 allows the humidity within the growing chamber to be less in the center where the root ball is most susceptible to water stress . the unraised portion 31 is where moisture is taken up through the growing medium into the growing chamber . the actual growing chamber itself starts at the top of the raised portion 29 . below this point is the water / nutrient reservoir , which functions as part of the growing chamber as the liquid level decreases to empty . the slots 27 are for oxygen circulation through the growing medium 5 . if there are too few slots 27 , the plant will starve for oxygen . if there are too many , the humidity will go down below acceptable levels and the liquid consumption will increase . the aeration openings 27 must start at or below the optimum liquid level and run well above the maximum allowed level of liquid in the planter , preferably at least twice the height of the raised portion 29 . in the preferred embodiment , it will be seen that the aeration slots 27 begin approximately one - half inch from the bottom of the liner and are four inches in length ; thus approximately three inches of each slot 27 is not immersed in liquid when the system is initially filled . for a particular growing medium 5 , the amount of liquid drawn into the system by capillary action is controlled by the relative areas of the raised portion 29 and the lower portion 31 of the bottom wall 13 . to permit more liquid to be drawn into the growing medium 5 , the area of the lower portion 31 may be increased ; to permit less liquid to be drawn into the growing medium 5 , the area of the lower portion 31 may be decreased . when the liquid level in the outer pot 9 falls to one - quarter inch , the growing medium 5 no longer picks up the liquid and begins to dry , through the circulation of air through the aeration slots 27 , through the gap between the liner 3 and the outer pot 9 , and through the growing medium itself , and through transpiration of the plant 10 growing in the medium . nonetheless , the longest rod 45 continues to indicate the presence of liquid . therefore , when the rod 45 finally becomes bright , and liquid is added , the growing medium 5 has been out of liquid for about a week and has dried about ten to twenty percent . this cycle greatly enhances root growth and plant health . numerous variations , within the scope of the appended claims , will be apparent to those skilled in the art in light of the foregoing description and accompanying drawings . merely by way of example , the inner and outer pot combination and geometry may be utilized with other growing media and other liquid level meters , with or without a light meter . the aeration openings may be formed as a series of holes , placed more or less randomly around the wall of the liner 3 . the raised part of the bottom wall of the liner 3 may be formed as multiple raised parts and positioned differently . the expanded slate growing medium may be utilized with other hydroculture systems . the light / liquid meter may be used with other hydroculture systems , or even with entirely different growing systems . numerous changes can be made in the light / liquid meter . for example , connecting body 26 need not be stepped . the light transmitting rods may be clear or tinted , or may have a colored or opaque coating applied thereto , for example to color code the meanings of the rods . the upper indicating surface may have a clear or colored lens affixed thereto , or a part of the upper surface may be frosted to intensify the difference between its &# 34 ; dark &# 34 ; appearance and its &# 34 ; light &# 34 ; appearance . if desired , the connector 47 may include an indicator showing the proper appearance of the indicating surfaces 49 when sufficient light is present . a fourth , short , rod may be included as a reference . conversely , only two rods may be used if liquid is added slowly and the rods watched carefully . if no provision has been made in the hydroculture system to accept connector body 47 , it may be modified to be placed in the system in the location previously used by the prior art float type indicator , for example by providing it with a hook or slot to affix the meter 7 to the rim of the inner or outer pot of a planting system . an opaque housing may be placed around all the rods , in lieu of separate coatings on each rod , particularly if the rods are bunched , rather than being arranged in a line . neither the coating nor the housing is necessary if care is taken to prevent light leakage into the space between the inner and outer pots .
a hydroponic planter includes an outer container and an inner liner . the liner includes a central inverted cup - shaped reservoir for a liquid nutrient solution . the outer wall of the liner includes slots extending substantially above the height of the reservoir , to provide aeration of the roots of plants growing in the planter . a combined light and liquid level indicator determines the minimum amount of light in which the planter can be placed , shows when to add nutrient solution to the planter , and indicates when too little , sufficient or too much nutrient solution has been added . the light / liquid level monitor includes three light - transmitting rods of different lengths extending between the outer container and the liner ; one extends to the bottom of the liner , another to below the top of the reservoir , and the third to near the top of the reservoir . the rods have flat upper indicating surfaces and conical ends so that the indicating surface becomes dark in appearance when the conical end is immersed in liquid .