Seedlings need water

The Progress-Index - At Home - - Front Page - LEE RE­ICH

Ready. Set. Go. Grow­ing seedlings in­doors seems al­most like a race. Of course, it has a stag­gered start, with onions al­ready grow­ing strongly and to­ma­toes not yet sown.

Wa­ter­ing th­ese seedlings is cru­cial: Timely wa­ter­ing keeps them chug­ging along apace; two or three days of ne­glect could spell death.

A sim­ple way to au­to­mat­i­cally water seedlings is to rely on the soil to draw water up from be­low by cap­il­lary ac­tion. This is just how var­i­ous types of com­mer­cially avail­able seedling-grow­ing kits work (avail­able on­line from such sites as gar­den­, lee­val­, and charleysgreen­

Soil wa­tered by cap­il­lary ac­tion stays con­stantly moist, rather than swing­ing be­tween the ex­tremes of hav­ing plant roots cry out for air and then for water.

Let capillarity work for you

Cap­il­lary wa­ter­ing it­self is noth­ing new. For years, cap­il­lary mat­ting — a thick, water-ab­sorbent fab­ric that does not rot — has been avail­able, mostly to com­mer­cial green­house grow­ers. The idea is to let one end of the fab­ric dip down into a water reser­voir while the re­main­der rests flat on a hor­i­zon­tal sur­face. Pots of plants sit on the flat mat. If the pots like­wise have flat bot­toms and the soil within is right up against the bot­tom of the pots, then a cap­il­lary water con­nec­tion is es­tab­lished through­out. As plants drink in water, it is re­plen­ished by water drawn up from the mat which is, in turn, drawn up from the reser­voir.

Th­ese cap­il­lary-wa­ter­ing seed starters are nifty set­ups that make it con­ve­nient to raise seedlings in your home. A small plas­tic pan holds water. Into the pan fits a Sty­ro­foam or plas­tic “ta­ble” on which sits the mat, with one end dip­ping into the water. A multi-celled Sty­ro­foam or plas­tic plant­ing tray sits atop the mat.

The whole setup is about the size of a three-ring note­book, or half that, de­pend­ing on the num­ber and size of the cells. Right

now, my broc­coli, Brus­sels sprouts, cab­bage and kale seedlings — 24 seedlings in about a square foot of space — are grow­ing in 1-1/2 inch square cells. In about a month, I’ll have cu­cum­bers and mel­ons started in prop­a­ga­tors with slightly larger cells.

A few other features round out th­ese sys­tems. A clear plas­tic cover main­tains hu­mid­ity while seeds are ger­mi­nat­ing, then tucks neatly out of the way un­der the reser­voir. The un­der­side of the “ta­ble” looks like a peg­board, and can be flipped over to pop seedlings up out of their cells when they are ready for trans­plant­ing. Plant roots knit the soil to­gether to keep it in­tact dur­ing trans­plant­ing. And af­ter a good clean­ing, the whole setup is ready for re-use year af­ter year.

A few cau­tion­ary notes

Cap­il­lary wa­ter­ing does have draw­backs. Water evap­o­rat­ing at the sur­face of the soil leaves fer­til­izer salt residues. Th­ese residues can ac­cu­mu­late in the soil and draw water out of the roots the same way potato chips dry out your lips. Seedlings gen­er­ally do not spend enough time in con­tain­ers to bring on this prob­lem, es­pe­cially when care is taken not to over-fer­til­ize. If nec­es­sary, oc­ca­sional wa­ter­ing from above will wash the salts down and out of the soil.

An­other prob­lem is that of seedling roots grow­ing out through the bot­tom of their cells and into the mat­ting. Then plants be­come dif­fi­cult to re­move from their cells and lose too many roots when they are fi­nally ripped away. I avert this prob­lem by pe­ri­od­i­cally lift­ing the plant­ing tray up off the mat be­gin­ning when the seedlings are large enough for their roots to bind the soil to­gether.

Per­haps the worst threat to any au­to­mated sys­tem is ne­glect. I have al­most lost seedlings from for­get­ting to check the water level in the reser­voir, which only needs to be done about weekly. It’s easy to for­get about wa­ter­ing when so much of the job is done for you.

De­spite th­ese mi­nor short­com­ings, th­ese cap­il­lary wa­ter­ing sys­tems for rais­ing seedlings are among the few hor­ti­cul­tural gizmos that I rec­om­mend. Be­fore I used them, my seedlings teth­ered me to my house daily through­out April and May.


Wa­ter­ing th­ese seedlings is cru­cial as two or three days of ne­glect could spell death. A sim­ple way to au­to­mat­i­cally water seedlings is to rely on the soil to draw water up from be­low by cap­il­lary ac­tion.

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