Watering with boiling water

[John85]

Not the plants of course!
I read that a cheap way to kill the seeds of the weeds in your sowing pots or trays is to water them with boiling water before sowing.It should kill the unwanted seeds in the top inch of the compost.
Has someone tried this and what where the results?

[maggiepie]

I use boiling water in my potting mix before I use it, hopefully it kills any fungus gnat eggs that might be in it.
It seems to work.

[Kristl Walek]

I use boiling water in my potting mix before I use it, hopefully it kills any fungus gnat eggs that might be in it.
It seems to work.

I too always filled a large bucket with bagged seedless seedling mix and poured boiling water over it---partially to properly moisten it (as the pre-prepared mix does not wet down easily), but in the hopes it might kill fungus gnats (which it never did). Because weeds did not usually sprout out of these mixes, I am unsure what effect it would have on weed seed.

[Palustris]

Never tired it on compost for seed sowing, but in the days when I grew Ferns from spores, it was standard practice to sterilise the compost this way before sowing the  spores. The idea was to kill off any stray spores of unwanted stuff. It seemed to work for Ferns.

[Tim Ingram]

I've also done it for ferns and very fine seed like ramonda, and a few ericaceous species. I've always kept the seedpots in covered prop. boxes so you don't get liverwort and moss spores (and ferns!) coming back in. But good seed compost should have been sterilised already.

[maggiepie]

I too always filled a large bucket with bagged seedless seedling mix and poured boiling water over it---partially to properly moisten it (as the pre-prepared mix does not wet down easily), but in the hopes it might kill fungus gnats (which it never did).

Kristl, I do mine in a fairly big rubbermaid bin with a lid.
I usually use bales of promix, the mix stays very hot for quite a long time with the lid on, maybe that helps kill the eggs or maybe there aren't any.

[johnw]

Helen - If you're using the Promix W/MYCORISE the booiling water will knock the fungi flat.  Boiling water has never killed the gnat eggs here. They must be in the promix as I pot and bag and the gnats appear a few weeks later.

johnw

[Kristl Walek]

Some years ago when fungus gnats started to be a regular problem with commercial mixes, I started using Safers Sticky Strips regularly.

They go in the pot/flat the second I sow something. I have found that if I do not neglect to do it right away, the first batch of gnats that hatch out are killed & the problem is usually nipped in the bud. If you let the population breed---it gets almost impossible to control them.

I cut them into tiny pieces and attach them to a recycled label and the insects get stuck. A flat gets a few.

A simple, old-fashioned principle that works really well for flying pests.

[maggiepie]

John, I do use the promix with the Mycorise, I figured the boiling water would kill that but from what I gather it has a limited life anyway?
Not sure how old the promix bales are when purchased.
The reason I think the boiling water works is that the only time I got lazy and didn't do it, I had gnats appear a few weeks after using it.
I have none at the moment ( hope murphy isn't around)
Maybe I am seeing what I want to see?

[Ezeiza]

The method is standard in organic production and is called "surface sterilization". It is very effective depending on the really hot water reaching the whole volume of mix. Helen is doing things properly. If you do it outdoors, do not use enough water, or let the water cool down before application, it will not work.