Harry, The big concern with re-using planting mix is disease. If last year's tomato was healthy...I re-use. Many discussions on container size...5 gal buckets are best suited for determinate tomato plants. They can work.Undoubtedly, bigger is better. I use 15 gal nursery pots...which works great. Container plants require more watering, feeding, and attention. However, it is not hard to have good success.

Fair point about disease. It would be smart to sterilize the soil before you use it. Get soil temp to 200F for an hour. I *always* sterilize the soil I use before putting seeds in it. That doesn't just kill disease, but all kinds of crap (fungus, mold spores, other bacteria, bugs) that you don't want with your seedlings.

I don't garden much anymore but I used to put a large pan of used soil in my oven - with the windows open - and bake until the soil reaches 200 degrees with your thermometer. It can save you tons of money. (Windows open to keep the "earthy" smell out of the house.) Mix in some new potting soil after the old has cooled.

This will also keep stray seeds from last year from growing with your good seeds.

If the the the potting soil was soil less mix, i would re use it. Just clean up the old roots and maybe add little new soil.

About the disease, depends on what the disease was. Most tomato diseases are airborne bacteria (early and late blight) which would not overwinter in soil.

Seysonn

Agree that these are common questions and lots of info here that the search will pull up for you if you want to read through it. Same goes for container size. Plus the Container gardening forum has even more info on container size questions. In general, 5 gallons only if no other option. 8-10 gallons minimum is recommended. Bigger is better.

Also agree that soil sterilization is usually a waste of time as most common diseases are airborne fungus. But if you wish to do it pouring boiling water through it is much easier and less stinky.

Re-using the potting soil IF it was instead a soil-less potting mix as it should be, and NOT soil/dirt, is quite common and only requires some refreshing. Many of us dump out the containers and mix in about 1/3 to 1/2 fresh mix and then refill containers.

As to when to start seeds - 6-8 weeks prior to your last frost date or your plant out date.

Dave

I sometimes tend to get mold growing on my soil if I don't sterilize. The fungi that are responsible for damping off can certainly overwinter in soil. Never had a stink out of sterilizing soil in my oven, but maybe we use different compost. I also have an outdoor oven, so that helps, I guess.

I should add that nurseries around here ALWAYS take steps to sterilize their soil for planting, though they usually do it with steam generators, rather than heat. Methyl bromide can be used as well, but that's dangerous stuff.

Soil sterilizing might be helpful when you are germinating and growing seedlings. I do that myself. But when I re pot them (to 1/4 gall or bigger), or plant them outside (permanent container) I use just regular potting mix.

Seysonn

Ah yes, I was thinking that he was just starting seeds (which was the question he was asking at the end), but indeed, he's filling pots. Yes, sterilizing big pots worth of soil might be a lot of trouble.

Thanks to all for the feed-back,
I will try to have a look at some of those other forums you mentioned. If I'm not careful I could be on here for hours at a time.....theres soooo much to read and write about!
As for my planting, I'll use soiless seed mix to start my seeds then plant into some potting soil when they get true leaves. When I get them outside (into their bigger homes) is when I would like to use last years potting mix. I really don't want to put any of that potting mix into a hot oven or treat with boiling water after building the "health" of that soil last year with the addition of compost and home-grown worm castings etc.!!
Harry

Way to go Harry.
I personally wouldn't bring in any used potting soil for for starting or re potting while seedlings/plants are inside .

Seysonn

Since my last comment I have learned that Hydrogen Peroxide can be beneficial on killing MOLD, because mold is both soil and airborne. In WET PNW weather we get a lot of mold, especially towards the end of season. So H2O2 can come to rescue

The only way too prevent air borne diseases (blights) is systematic programmed spraying with fungicides like Neem Oil and Daconil. I should take my own advice and do it diligently this coming season.

Seysonn

Not entirely clear to me why a half-hour in a 200F oven makes your compost- and worm-casting-improved soil any less healthy. Hot water and H2O2 will do essentially the same thing to it. I bake soil routinely for seedlings, and have never had any problems. I have to assume that such heating would be just as effective as any fungicide.

This year I also baked my soil for indoor use. Haven't seen any insects. Last year I w.as fighting fungus gnat. I also soaked starter soil with peroxide solution.
Baking soil at 200- 250F will destroy any microbes in the soil, good or bad. .I find things like fungus gnat flying around very annoying beside the damage they cause .

Sysonn