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Watering Houseplants Part 3: Watering From Below

white crust on houseplant pot, how to water houseplants, monadenium
One of the biggest disservices that I do my houseplants is watering them from below. Even though I know better sometimes I can't resist the urge to fill the sink or a large container with water and setting the plants in the water to get a drink. Watering houseplants from below is a time saver if you have a lot of plants to deal with but you should avoid it when possible.

If like me, you're in the habit of setting your pots in water you may find that a white crust develops on your pots, in bad cases the white stuff will collect on your plant. In the photo above the first image shows the development of a hard white substance on a Monadenium in my collection. In the second photograph the white crust has developed on the terracotta pot of a cacti but if you look closer there is also a brown gunk growing on the cacti. Sometimes when you water too much or when water doesn't drain properly a green slime will also develop on the surface of the soil.

The crusty white substance on my succulent plant and on the terracotta pot are minerals that have collected from the hard water that comes from the tap and fertilizers. When you set your plant in water you allow for minerals and chemicals to collect in the pot and soil instead of being washed out. These soluble salts (like fertilizer) stay behind when water evaporates and eventually the high concentration of these salts in the soil make it hard for the plant to take up water. Soluble salts damage the roots of your houseplants and weaken them to the point where they are vulnerable to pests and diseases. Reduced growth, brown tips and dropping of lower leaves are all signs of high soluble salts concentrated in the soil.

You can remedy this by following these steps:

Avoid setting your houseplants in water when they need watering and don't ever let them stand in water. Make sure you're following the directions on the package of your houseplant fertilizer. If you use commercially available houseplant soil check to see if it comes premixed with fertilizer granules. Don't skimp on your houseplant soil-buy the best you can afford and amend it with perlite. When you water use distilled water or set it out overnight to allow for chlorine to evaporate.

You can remove the white crust from your pots by using a stiff sponge that is moistened and scrapping away the crust or starting over in a new pot. Sometimes when you bring a houseplant home from a greenhouse that has been sitting in water or not taken care of properly you'll find that the soluble salts have already accumulated. In those instances I will usually just slip the plant into a pot that is the same size as the one it is growing in until I can transplant it. Every New Year's Eve I make a resolution to stop watering my houseplants from below-maybe this year I'll keep my resolution.

Previous Posts

Watering Houseplants Part 1: Pick Them Up
Watering Houseplants Part 2: Botanicalls


  1. Anonymous4:55 PM

    Watering plants from below is fine, you just have to ensure it's not getting overwatered and, like you said, salts are purged on occasion. I have a number of houseplants growing in subirrigation (the technical term for watering from below) and they're doing quite well. Less mess, too.

  2. I recently started reading 'On Origin of species' by Darwin and it has so much about plants and their form and shape and the cause behind 'em.

  3. Sam,

    What are you using a self-watering pot or did you design something on your own?


    Thanks for posting because you just reminded me that I wanted to pick up that book. I've never read it but recently I was reading something about carnivorous plants and the article I was reading was inferring that they many didn't develop the 'pitchers' to catch bugs on purpose. I'll have to see if I can find the page in my browser history again.

  4. Anonymous7:45 PM

    At least you water your houseplants. For some weird reason, I can grow all kinds of things in our garden, but when it comes to houseplants, I pay them no attention (like watering them) and they have short lives.

    I feel guilty now.

  5. Aaaaah, now I understand. Hm, I'll have to continue with my selfwatering containers, but change my cleaning routines a bit. Perhaps I even should use demineralised water every now and then - I have a source for that called dryer :-) . I haven't had this crust problem for a long time though, probably because growing vegetables requires redigging and mixing new soil pretty often.

  6. Great post with a lot of valuable info. I have some cacti (the ones with a lot of wool) that I do water from the bottom because watering from the top causes rot since all the moisture gets trapped in the wool for too long a time. In this climate the pots dry so fast I don't think we have as much danger of root rot.

  7. Hrmm.. i guess i had the wrong idea about watering from the bottom and i am kinda confused.
    I had always been told to water from the bottom because you want well established roots with even growth in the pot (being that the roots reach for the water). i repot my plants once a year but check every six months if they need it sooner. I have noticed the ones that i water from the top have top shallow root systems and grow slower and such but the ones that i have watered from the bottom have a nice long reaching root system. I clean the minerals as much as i can and even have experimented in a double pot system that kinda catches the deposite at the bottom (where i plant the plant in a regular plastic pot but put that into a terracotta pot that has drainage, water it from the bottom as i do normally and in theory the porous terracotta kinda caught the mineral and salt from the inside and out.)
    Any ideas if my old lessons are any true or could i just be hurting my plants?


  8. Krista,

    No, you are right. I'm a firm believer of watering from below because of what you mention with the roots.

  9. Anonymous7:54 PM

    Watering from below prevents root spiraling when it reaches the edge of the pot, and thus the plant being eventually rootbound. If you switch to distilled water or reverse osmosis, you won't have mineral buildup. Your plants will thank you.



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