Rainwater for house plants, white mold in soil.

So I decided to collect rainwater for my houseplants. Now all my plants are starting to get white fungus or mold growing in the soil. Is this typical when using rainwater? How long can rainwater hold before it gets bad?

No it's not typical. Are you over watering? What's the humidity like? I use rainwater as much as posible and never have that issue.

My biggest concern with rain water is mosquito larvae. There would have to be leaves or sticks, some kind of organic matter to produce something like mold. Can you add a pic of the soil?

I collect rain water for my aquariums, and have used rain water collected several months ago. Rain water does not go bad unless there is something in there (as suggested: leaves, sticks) or other stuff that rots.

White mold on the soil suggests over watering.
If it is white salt build up then this would be really odd, unless you are adding too much fertilizer to the rain water.

I really don't think I am overwatering. I'm not that new to caring for houseplants, but of cause, if that is the most obvious reason, I might have been overwatering.

I collecet rainwater from my roof which via a chain dripples down to a wateringcan on the ground. Maybe that is a bad way to collect, since stuff can drop down in the can too.

As long as the can gets emptied completely, I don't see how that would cause any problems, or could be connected to any kind of mold, but I may not be picturing things as they are. Sounds unlikely though, and unless your sense of smell is extremely weak, you would smell a foul odor if there was decomposition like that happening in your watering can.

So yeah that does look like some kind of mold. There must be some kind of organic matter in the pot which is decomposing this way. The mold itself is unrelated to the plant, but the conditions that allow it to grow may not be great for the plant. If the plant looks healthy, I would try watering a little less often. If your plant is kind of pale, there may be 'too much nature' going on in this pot. Decomposition can temporarily rob plants of nitrogen, causing chlorosis.

Looks like it's a Schefflera? How does it look?

Is there a nursery pot inside a cache pot? Do you remove the inner pot when watering this plant? If not, water sitting at the bottom could be part of what's going on. Removing the inner pot and watering at a sink prevents that from happening, as well as allowing any unused substances in the pot to wash away. That's much less likely with rain water, but with organic matter in a pot, there may be tannins or other substances that would be best if flushed out.

purpleinopp,
If you use mosquito dunks in your rain buckets it'll kill any larvae and prevent future larvae. I use them for my carnovorous plant water trays and indoor watering can.

Thanks, Tommy! I use the water before that becomes an issue, and very much enjoy ruining however many mosquito larvae are in the water. Whatever isn't used by the time wigglers appear gets put in jugs with lids, poured on thirsty plants in the ground. That's what I meant by concern, that it's something that needs to be addressed, not that I was soliciting suggestions about what to do, but if I read that I would want to offer suggestions too. Can there be too much said about preventing/destroying mosquitoes? I think not, friend!

I've heard of this stuff before though and just thought to wonder. Does it kill the larvae once eggs are laid, or does it prevent mosquitoes from wanting to lay eggs in the water to begin with?

A piece of screen would keep mosquitoes out if one didn't want to spend money on the dunk product.

Baby birds can also drown in rain collection buckets/barrels, so those who want to drown mosquito larvae but prevent bird access could use a wire mesh with bigger openings than window screen, like chicken wire.

Carniverous plants sound cool. I haven't had or even seen any for decades. A plant that eats flies would grow like crazy around here. How do you find those kinds of plants?

Here is one source for carnivorous plants.

http://www.californiacarnivores.com/

I also would suggest watering that plant less often. Most molds need more water than most plants do.

Well, the plant does seem to thrive. I have only had for a month or so and it's still a very small plant.
The other picture shows how I collect rainwater. Maybe it is too unsafe a method to use since organic stuff can fall in the can and make the water bad. A full can like that does take me a couple of weeks to use.

A few of my other plants, three in total, has got the same symptoms as this one. I just find it hard to believe I should have overwatered three plants. I can't remember when I since did something like that. It also happened a week after I started with rainwater. And now I can see a few leafes and sticks in the bottom of the can.

Maybe I should get some kinda mesh to attach ontop of the hole of the can so that stuff can not get in.

Oh, and from now on I will water the plant over the sink.

Did you repot the plants when you got them, into bigger pots? The fresh organic matter would definitely explain mold showing up after about a month of being moist. This should go away as the organic matter finishes decomposing. It's not your fault if the soil is taking a while to dry, it happens with most bagged potting soil. It's not overwatering, it's underdrying. Water sitting between the two pots would not help the situation either, if that has happened. The new soil that the roots haven't penetrated yet is a tricky thing to deal with after a repot sometimes. Letting the plants get more dry will encourage the roots to seek that moist soil so the whole thing starts to dry more evenly.

Unless the water is turning brown from leaves sitting in it, from tannic acid, it should be fine. Just take the leaves or sticks out if you see them. There can't be many falling in the small hole of that can.

Letting plants drip at a sink when watering should help the plants a lot, both with getting rid of as much excess moisture as possible, and allowing any excess substances produced by the decomposing organic matter (tannin possibly comes into play again) to escape the pot.

Your metal sculpture thing is really cool!

I have 5 60gallon rain barrels that I collect rain water from the roof via the downspouts. I use the water in my garden (gravity feed) and for my container gardens and houseplants. Everything seems to do well with the rainwater but the orchids especially seem to like it.
I use nylon screening from HD. It comes in a roll and isn't expensive. It cuts with scissors and duct tape secures the edges. I let the water from the downspouts run through the screen which catches a lot of debris. I also have had several chipmunks drown in buckets of water they couldn't escape :-( and the screen not only keeps the birds out of the barrels but has probably saved a few chipmunks too.
I would guess that the mold is from the soil and not the water. I think the soil is too wet with improper drainage as talked about earlier. Always better to ere on the side of dryness when it comes to most plants in pots.
I am just seeing you are from Denmark. I doubt you guys have Home Depot there. Does your watering can overflow or do you use it up before it fills up?

Purpleinopp, the sculpture is actually two seperate candleholders (my vocabulary lack a better word) which can, as you see, cross eachother. I like them, too.

I always repot plants as soon as I get home. I use my own mix of normal soil in a bag, lots of barkchips and perllite.
But you right about the pot in the cachepot, I need to be careful no water sits there for too long when watering.

Helenchild, I don't even know what a home depot is :0)
Me using rainwater is very new, I have only used like to cans of water. Both times the can overflow overnight.

Thanks for all your posts.

FYI

http://en.wikipedia.org/wiki/The_Home_Depot

Helen, so sorry about the chippy - they are so cute! My Mom says she has seen some in her yard a few miles away, but I've never seen one here. There are a ton of wild cats in my neighborhood, hers seems much less inundated by that curse. That's definitely another reason to have some kind of cover over standing water buckets/barrels/cans. Drowning mosquitoes = good. Drowning birds & chippies = sad, avoidable. Thanks for sharing the info.

One of these days I'd like to have the kind of rain barrel that has a hose attached to it, dabbling with buckets & plastic trash cans still. Then I wouldn't bother with dumping the excess when wigglers show up in it 'cuz I'd have a smaller-gauge screen cover to prevent them from showing up at all, like you said. Just started doing this in earnest last year but it hardly rained all summer. This summer, I haven't had to put tap water on potted plants at all. Very cool! Free and 'better' water. Now I know how much water is needed/used too. About 5 gallons per day, although I don't water stuff every day. Not that this amount of water costs much $, but I like to know, and over the course of a whole summer, that's a savings worth the minor effort to me.

There's no HD around here either. That kind of screen roll you mention would probably be at a hardware store though. A twine potato sack could probably work if they sell potatoes that way in Denmark. I was in Denmark once, but too busy looking at the bulb flowers to shop!

MadsH, bark chips will definitely form molds if kept moist. Unless there's water sitting between the pots, the bark chips should dry quickly enough that mold is unable to grow visibly. Don't think it was discussed what the other plant(s) is, but Schefflera definitely does not like to be moist all of the time, in any kind of soil. I almost always repot immediately for new plants too. The little store pot is usually full of roots needing more room to grow, and my plants are outside most of the year, so need to be heavy enough so they stay on the porch. Knowing about the soil used and the timing of the repot does help us understand what's going on though.

That looks like an awesome window for plants, BTW! I think any Scheff would be glad to call it home.

Kind of funny, this could have just been a blurb, "let it dry out more, more often." But I think all of the reasons 'why' are so interesting. After gardening for so long, I'm almost more interested in 'dirt' than plants because without 'good dirt,' there are no 'good plants' whether in the ground or in a pot. It's just a lot more complicated, much less room for error, in a pot, and things don't work the same way.

So speaking of ground growing, do you have any of those fantastic bulbs out there for which your country is famous?

This message was edited Oct 4, 2013 9:33 AM

purpleinopp,
The mosquito dunks will kill any wigglers already in the water and prevent future larvae. I put one quarter of one in each of my 5 gallon buckets and 1/8th of one in my indoor watering can.

Purpleinopp, please explain what you mean with "bulbs" and I will answer your post. I know what bulbs IS, but I don't quite understand your question - and didn't even know "my" country was famous for bulbs.
Which bulbs exactly are you think of?

Thanks again, Tommy!

MadH, I'm pretty sure 'Denmark' is one of the cultivars often available in Tulip displays, pretty sure I had some in OH, I always liked the 2-tone kind of any color. But if you are IN Denmark, you might not see them sold that way. I think those BBS displays are a USA thing, not really sure, sorry for the confusion.

What an interesting discussion. I'm wondering if the mold in the pots occurring at the same time as you started to use rainwater was not simply a coincidence. Many, many molds are airborne, especially the ones that grow on the surface of the soil as opposed to under the surface. (Those would be the kinds that turn up with new potting medium.) There's nothing about rainwater that would promote mold, I don't believe. And it is true that mold most often grows on houseplants in which the soil is too wet.

But I'd like to address a couple of things you all were talking about. The first is ' the plant in a cachepot, water sitting in there, take it to the sink to water it and let the water drain' thing.

I've been an interior landscaper for 30 years - we're the people who take care of all the live plants in commercial situations. Probably 95% of those plants are "double potted" - that's where the plant in its grow pot is placed into a plastic liner, and both are set inside a decorative container. When the plant is watered the water runs into the liner, and is never emptied. The plant uses that water before its next watering. Here's how it works. http://www.youtube.com/watch?v=IbA2GkogUHg

The technician must ALWAYS check the soil moisture before adding more water, and must learn the correct amount of water to add so that the soil dries out to the level necessary for optimum plant health between waterings.

The key to controlling salt build up is to not fertilize too much. Very few plants are fertilized more than 4 times a year. The majority of moderate-to-low light plants are fertilized only 1 or 2 times a year. Thus running water through the plant to rinse out the fertilizer is not necessary either.

Some people think that interiorscapers aren't really interested in keeping plants alive for a long time, or that they keep them at a bare subsistence level, etc,etc., so I'm going to try to explain a little about professional plant care. Fact A is that if the clients' plants don't look beautiful, they will get another company. Fact B is that there is a very small profit margin in the business. Fact C is that finding new customers is extremely difficult. Fact D is that replacing plants is very expensive.

What these facts mean is that you must keep your clients' plants looking beautiful, and keep each plant on the account as long as possible.

I'm just trying to show you that you don't have to empty the cachepot, or carry plants to the sink to water them. You can if you want to, you just don't have to. What you do have to do, if you want your houseplants to survive, is figure out some way to monitor soil moisture.

Thanks for your post. I guess, it has nothing to do with the rainwater. Weird thing is, I scraped around with my finger on the mold to make it not visable and it never came back.
Now Im dealing with those little flies which typically comes when overwatering. Ive added some microorganisms to the water which should take care of them by eating the larvas.

I must have been overwatering the plant, it just doesnt look like me doing that kinda stuff. Also, the plant is quite new on the picture, maybe a couple of weeks, but I always repot plants when I have brung'em home. Saying this because these flies also typically can come from plants bought in supermarkets, but since I changes to soil when I got it, it must have been me overwatering. Just thought it would take longer before those flies start to come.