How to water

Light sprinkles don't reach the whole root ball. The fix is to water less often and far more thoroughly.

A light daily splash wets the top of the mix without reaching the whole root ball, and frequent light waterings tend to leave the roots shallow and weak (UConn Home & Garden Education Center, n.d.). The fix is to water less often, and far more thoroughly when you do.

Water thoroughly, then let it drain

When it's time, keep pouring until water runs out of the drainage hole, so the whole soil mass gets wet, not just the top inch (2.5 cm) (Trinklein, 2017). Letting some water run out the bottom does a second job, too: it carries dissolved salts out of the pot rather than leaving them to build up (University of Maryland Extension, 2023), which is the salt problem we'll get to in Lesson 7. How much runoff is enough depends on how salty your water is. Nursery guidance for container crops suggests letting about a tenth of what you pour run out when the water is low in salts, rising to three-tenths for the saltiest water (Owen et al., 2019). Those figures come from commercial nurseries, not living rooms, but the point carries over: water enough to moisten the whole pot, plus a little extra to move salts out (Davison, 1998).

Then let it drain, and empty the saucer or cachepot (the decorative outer pot). Extension guidance says to tip out the excess within about 30 to 45 minutes (Iowa State University Extension and Outreach, n.d.), or within an hour or so (UConn Home & Garden Education Center, n.d.). Water left standing in the saucer is drawn back up into the pot, which keeps the mix wet and leads to root rot and salt injury (Davison, 1998). Roots that sit in water for long periods rot (Iowa State University Extension and Outreach, n.d.).

Top watering versus bottom watering

You can water from the top, the usual way, or from the bottom, by setting the pot in a tray of water until the surface of the mix turns moist, then taking it out and letting it drain (Trinklein, 2017). Bottom watering makes sure the whole soil mass gets wet (Trinklein, 2017), and it's the method recommended for plants that can't tolerate wet leaves, such as African violets, and for rewetting a mix that has dried out so hard it sheds water (Criscione & Holliday-Goulart, n.d.).

It has one catch worth knowing. Watering from the bottom can let soluble salts build up in the mix and on its surface (PlantTalk Colorado, n.d.). The same source says top watering is generally the better choice, and that if you water from the bottom, you should water from the top now and then to leach the salts out (PlantTalk Colorado, n.d.). So our routine is top watering by default, and bottom watering for the plants and the dried-out pots that need it, with a thorough top-watering from time to time.

Two pot cross-sections: top watering carries salts down and out the drainage holes; bottom watering wicks water up from a tray and draws salts up toward the surface.

Fig. 5. Top watering carries salts down and out the drainage holes; bottom watering wets the mix evenly but leaves salts to build up near the surface. If you bottom water, water from the top now and then to flush them out.

From memory Tier 1

Strengthen your understanding

Try these in your head first, then open to see.

You give your plant a small daily splash to be gentle. Why doesn't that work, and what's better?

Light waterings encourage shallow roots and don't wet the whole root ball. Water only when the mix has dried enough, and then water thoroughly, until water runs from the drainage holes, so the entire soil mass gets wet.

You water thoroughly and a little runs into the saucer. What do you do next, and why does it matter?

Empty the saucer once the pot has drained, within about half an hour to an hour. Water left standing there gets drawn back up into the pot and keeps the mix wet, which leads to root rot.

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