There isn't a simple answer to your question. I do believe that it's sometimes possible to rejuvenate a potting medium to extend its life. But, the medium has to be pretty darned sturdy in the first place. There are very few of those on the commercial market. Peat based media just don't cut it.

Ammendments should include such things as pine or fir bark fines, perlite, granite grit, etc. Stuff that creates porosity. Probably the most important elements in a productive potting medium are the pore spaces...voids. That's why most potting mixes just can't be reused ; they break down into tiny particles.

Now...all that being said....do you want to plant into disease contaminated soil? REALLY? Because it's still contaminated.

hey kent.. long time no see ...

they know its my favorite link ...

think dollar store turkey pan covered in alum foil.. giant jiffy pop ...

IF!!!! .. THEY TELL US THIS CAN BE ERADICATED BY HEAT..

i dont know.. and dont have time to google for you

ken

Here is a link that might be useful: link

Eighteen inch pot for 'some tomatoes'? That's too small unless you are planting something like tiny tim or other miniature variety. Or were you just thinking of using the soil? If it were a flower I'd not be too bothered for re-using potting mix. There isn't much to peat-based mix other than a growing matrix. You have to add the nutrients, it's just something to hold roots. But, I don't plant or start tomatoes in anything other than santised pots and new planting mix. They are just too susceptable to disease and it's not worth the savings to lose them from innoculation from some pre-existing crud.

How deep is your 18 inch diameter pot?

There are a couple ailments roses and tomatoes can give to each other (tobacco mosaic virus comes to mind) so I'd be inclined not to share soil between them.

tj