Pasteurising potting mixes - How to pasteurise home made potting mix

[Tamandco]

Hi Folks,

I've been making my own potting and seed raising mixes as recommended in 'The Permaculture Home Garden' by Linda Woodrow.

Can anyone suggestion a method for pasteurising the finished product to prevent weed seeds from germinating?

They are so much more vigorous and tend to take over whilst my purpose planted seed struggle to emerge. The weeds are very fragile when merely seedlings and difficult to weed out by hand until they are larger and by then they have already caused havoc.

I have thought about pouring boiling water over the mix prior to use. Has anyone else had experience with this method and if so, is the water from the kettle hot enough to kill any weeds seeds or do I have to wait til the weed seeds germinate first, then treat with the boiling water?

Does anyone have any other ideas or tips to help me overcome my problem?

Thanx,
Tam :)

[muttabuttasaurus]

Tam, if you get your compost hot enough for long enough, you should kill most if not all of the weed seeds in there. I think that boiling water to kill them would be energy inefficient if indeed it even worked. Some seeds need over 150 *C to be killed (I think).
There are various ways to successfully make a hot compost, but in general the key is to have enough of the right materials gathered all at once at the beginning. I think a ratio of 30 (carbon) to 1 (nitrogen) is good. Different materials have their own c:n ratio's, so the trick is to have a rough idea of each ingredients compostion and do a break down that gives you an overall 30:1 makeup.
Then you gotta get it all just moist, like a sponge so that when you squeeze it it will let out a couple of drops. Then turn it every few days until it cools off - usually in 10 days to 2 weeks. You could let it cure by sitting there for a few more weeks giving it a turn every now and then. Covering it with an old tarp until you use it will stop it getting infected by wind born seeds...
There are lots of good books about making compost and the best teacher is practise.
Good luck!

[muttabuttasaurus]

Tam, if you get your compost hot enough for long enough, you should kill most if not all of the weed seeds in there. I think that boiling water to kill them would be energy inefficient if indeed it even worked. Some seeds need over 100 *C to be killed (I think).
There are various ways to successfully make a hot compost, but in general the key is to have enough of the right materials gathered all at once at the beginning. I think a ratio of 30 (carbon) to 1 (nitrogen) is good. Different materials have their own c:n ratio's, so the trick is to have a rough idea of each ingredients compostion and do a break down that gives you an overall 30:1 makeup.
Then you gotta get it all just moist, like a sponge so that when you squeeze it it will let out a couple of drops. Then turn it every few days until it cools off - usually in 10 days to 2 weeks. You could let it cure by sitting there for a few more weeks giving it a turn every now and then. Covering it with an old tarp until you use it will stop it getting infected by wind born seeds...
There are lots of good books about making compost and the best teacher is practise.
Good luck!

[muttabuttasaurus]

If you are really determined to pasteurise the mix you already have I think maybe the simplest and most energy efficient way might be to put it in the oven. I'm not sure what temp.'s are required, but you could keep the mix at a hotter temperature for longer that way. But, you're going to kill a lot of helpful things in your mix that way too, and I don't know if I could ever be bothered to do that myself. I guess if those weeds are really buggering up your seedling production it might be worth it. Maybe you could make a simple solar oven to avoid contaminating your cooking oven. (of course, we should all be using solar ovens to cook in as much as is practical!)

[derekh]

To paterurise potting mix and kill pathogens, hold at between 60 - 65 deg Celcius for 30 minutes and hotter and you risk sterilizing the mix and killing off the good bacteria.

At college, we use steam - at home I would try solarising in a sealed heat absorbing container.

cheers
Derek

[Alexis Anderson]

Just a quick note,

if you are getting a lot of weed seeds germinating in your compost it may be a matter of fixing the problem before rather than after the problem.

Make sure that you don't add any weeds (or any plants for that matter) that have gone to seed into your compost. Try to harvest the biomass for your compost before it seeds.

If you have chooks you can throw your "seedy" material to the chooks. After a week they will have picked out most of the seeds (the most nutritious bit - they know without having to be told) and then chuck what is left over (but not any root material of things that send out runners eg couch) into the compost from there.

that most of us get Tomatoes and cucurbits sprouting out of old compost that has been made the "hot" way is a good indication that the system ain't perfect - so it is really best to take care of what goes in.

On another note I have been Wwoofing on a property where I have been using a "compost blokker" to make compost blocks in which to raise seedlings. It is a handheld tool with 4 spaces that you fill up with seed raising material (eg compost, sand and worm castings). You put this in you seedling box, and empty out the neatly formed compost blocks. You can then place a seed or two onto each compost block, and the seedlings grow nicely without getting tangled around one another + you can pot-up or plant out the compost blocks without disturbing the seedling roots.

You could fit about 70 of these compost blocks into an old cardboard apple tray sized 20cm X 50cm.

It was made in england, and I think the manufacturer's name was stamped on the tool. I'll try to find out the details and post it on the forum.

cheers

A