For April, 1921 



553 



A Lesson on the Plant In Relation To Water 



Being One of a Series of Lessons of a Home Study Course on Gardening. Appearing Regularly in The Gardeners' Chronicle 



Under the Direction of ARTHUR SMITH 



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AMONG the many factors which must exist in a plant's environ- 

 ment, if it is to make proper growth, it is not easy to define 

 one as being more important than another, inasmuch as the non- 

 existence of any one of them may to a greater or lesser extent 

 nullify the efTect of the remainder ; at the same time, water must 

 be considered as standing first. 



As in connection with all other good things, too much water 

 is as bad, or in many cases worse, than too little. Leaving out 

 of consideration aquatic and semi-aquatic plants, excessive water 

 in the soil destroys the roots of plants. We have previously seen 

 that oxygen is absolutely necessary to the life of roots, as since 

 the cells of newly-formed roots are lllled with protoplasm, they 

 must have access to the oxygen of the air or they can neither live 

 nor grow. When the soil cavities are filled with water, the roots 

 are soon deprived of oxygen, because the little oxygen contained 

 in the water is soon exhausted. A soil in this condition is known 

 as waterlo.gged, and smothering and decay of the roots soon fol- 

 low. Seeds planted under such conditions usually fail. The soil 

 water which is most useful to land plants is that which remains 

 attached to the soil particles after percolation has nearly ceased, 

 known as capillary water. Such water is well aerated because 

 it is interspersed with cavities which are filled with moist air, 

 such cavities being, if the soil is properly tilled, in communication 

 with the air above the soil. The root hairs apply themselves in- 

 timately to the wet surfaces of the soil particles, or reach out into 

 cavities filled with saturated air. and are thus able to draw- in the 

 well-aerated soil water, with its dissolved food constituents, in 

 sufficient quantity to restore loss from transpiration through the 

 leaves and to distend the newly formed cells. 



In the open ground the first renlcdy for excessive soil water 

 may usually be found in under.ground drainage. This should lie 

 followed by deep and thorough digging which verv materially 

 helps the free passage of water through the soil. Digging is a 

 very simple operation to most minds, yet there are few gardening 

 operations which as a rule are worse carried out. It is rarely 

 done deep enough and nothing less than the depth of the fork or 

 spade should be permitted. The drainage of ground w'ith a 

 hard, compact subsoil is greatly facilitated by throwing the top 

 soil well forward when digging and then breaking up the subso'l 

 without bringing any of the latter to the surface. Upon land 

 always plowed at the same depth, whatever this depth may be, 

 the horse's feet and the weight of the plow create in many soils a 

 hard-pan impervious more or less to water, the remedv for 

 which is double plowing. Deep digging and plowing, together 

 with brcak'ng up the subsoil while of considerable assistance in 

 preventing the existence of a water-logged top-soil, do not in 

 the case of the more clavey soils do awav with the necessity for 

 pipe draining, the latter if properly carried out will last for more 

 than one life-time. 



The trouble of excessive so'l water in the oiicn ground often 

 occurs in potted plants, as the result of too compact soil or too 

 copious watering. The expert recognizes this condition by the 

 sour odor of the soil, by lifting the pot, or liy tapping the pot with 

 his knuckle. If the soil is soggy, the weight will betray the 

 fact, or the sound given out by the pot will be that of a compact 

 mass instead of a more or less hollow body, as is the case of a 

 pot of well aerated soil. To remedy the evil, repot the plant in 

 fresh soil of a proper condition, provi{ling abundant drainage at 

 the bottom of the pot. ^ 



Tiijudic'rus watering is perhaps the most comimorC cause of 

 failure in erowin.si potted plants. Some people too often assume 

 that the chief need of plants is frequent watering, and so give 

 water in spoonful doses as the surface soil of the pot appears 

 dry. without observing the state of the soil lieneath. Tlie roots of 

 the plant in the meantime may be smothering in a w'atcr-logged 

 so'l or starving from drought. If, owing to inexperience, the 

 condition of the soil cannot he determined by the means above 

 mentioned, the soil irsav be tipped out unon the hand without 

 disturbing the roots of the plant, by revcrsin.g the pot and gently 

 striking its rim on the edcc of the bench or tabic. The real 

 condition can then be readily determined. 



In all connections copious watering at considerable intervals are 

 preferable to frenuent slight waterings. It should never be for- 

 gotten, what we have mentioned several times hefore, that air is 

 as essential as water to the well-being of roots, and that the 

 soil, however porous, requires occas'onal ventilation. A consider- 



able quantity of water poured upon the surface soil of a potted 

 plant, in passing downward not only thoroughly moistens the 

 soil particles, but acts like a fiiston, forcing the vitiated air of the 

 soil cavity ahead of it and out through the drainage hole at the 

 bottom of the pot, while fresh air enters from above as the surplus 

 water passes out beneath. 



Rapidly-growing plants require more water and are less liable 

 to suffer from over-watering than slower-growing ones. During 

 the rest period plants should be given very little water. 



Some species require more water than others. The native 

 habitat of the plant is a partial guide to the amount of water 

 needed. Plants native to arid regions, as the Cacti and those from 

 treeless, rocky locations, require little water and are readily de- 

 stroyed by over-watering. Plants with narrow and tough leaves, 

 especially when the leaf-blade is vertically placed, do not, as a 

 rule, like much water ; plants with broad, leathery leaves prefer 

 a damp atmosphere rather than great moisture at the roots. 

 Succulent plants with hard epidermal cells, and thin-leaved plants 

 with a strong wooly covering of hairs, are also examples of 

 plants requiring little water. 



Excessive watering sometimes produces a dropsical condition 

 in the leaves of plants under glass. This is most likely to occur 

 in Winter, when sunlight is deficient, especially if the soil is kept 

 nearly or quite as warm as the air. Water accumulates in the 

 cells,' abnormally distending their walls, sometimes even to burst- 

 ing. An unnatural curling of the leaves, with yellow spots and 

 small wart-like excrescences on their surfaces, are some of the 

 symptoms of this trouble. Less water, increased light and re- 

 duced bottom heat furnish the remedy. 



Excessive moisture in the air and soil is injurious to plants, 

 since the former tends to hinder normal transpiration, and, com- 

 bined, they favor the growth of many diseases. 



On the other hand, i-isufficient moisture in the air causes 

 excessive transpiration, which reduces the tension of the cell- 

 walls and thus retards growth. It also tends to clog the leaves 

 with useless matters, causing their premature death. The effects 

 of insufficient moisture in the air are often very noticeable upon 

 plants kept in living rooms. Such plants, especially when few 

 in number, rarclv make satisfactory growth and the lower leaves 

 continually perish. Moistening the air by evaporating water in 

 the room, or setting the plants in a zinc tray covered with moist 

 sand usually remedies the trouble. 



Insufficient moisture in the open air rarely occurs unless there 

 is also a condition of extreme dryness in the soil. 



Insufficient moisture in the soil retards growth both by reducing 

 the tension of the cell-walls and by lessening the supply of food 

 from the soil. Therefore the tendency of drought is to starve 

 the plant. 



Drought hastens maturity, especially in annual plants, since it 

 favors flowering. Lettuce, sninach. and the like "run to seed" 

 earlier if insufficiently supplied with water. The crispness and 

 tenderness that give quality to salad plants, such as celery, lettuce, 

 radish, etc.. due to the distended condition of their cells, is largely 

 wanting when the water supply during growth has been insuffi- 

 cient. 



In periods of prolonged drought artificial watermg of plants 

 growing in the open ground inay become necessary, but this 

 should only be used as a las; resort, when other means of miti- 

 gating the effects of dry weather have been used and found to be 

 insufficient. 



Plants crowing upon a well-dniired and deeply cultivated soil 

 rarely suffer from drought, as this condition tends to cause the 

 roots to penetrate deeply and the cultivation prevents the evap- 

 oration of soil moisture from the surface. To the latter end the 

 soil between growing plants should be continuously hoed through- 

 out the season, which not onlv keens down weeds which rob the 

 plants of water, but creates what is know-n as a soil-mulch which 

 acts in ihe same way as a mulching of any material that is a slow 

 conductor of heat and moisture, such as straw, marsh hay. or 

 manure, w-hich are frequently snread between plants to prevent 

 the effects of drought. The maintninence of a soil mulch_ is the 

 fundamental principle of the dry-farming of the semi-arid dis- 

 tricts of the West, where on account of the sirall avera.ge annual 

 rain fall crops are grown on the same sround "onlv in alternate 

 years. The vear of no crop is devoted to keeping the soil thor- 

 oughly cultivated throughout the season by which means the 



