Add your old soil to your compost for outdoor growing. Wash out your container with a 10% bleach solution. Wash the surface that you set it on the same. While you have the bleach mixed, do your cages or whatever support system you are using. And Start with fresh mix.

Good sanitation is key, an ounce of prevention...

No need to clean out the mix from season to season. Just add extra to make up for what you lose when you pull up the root ball.
Obviously remove the fertilizer strip and re-apply every season.
Also re lime the mix.

I have used the same mix in my Earthbox for three years now.

If that's what you do, it's fine.

No offense but it's bad advice to give...

Some people just rinse the glass out and put it back in the cupboard. Plants are susceptible to pathogens just the same as we are.

Keep it clean!

Cheap insurance in my book.

I'm new to earthtainers, this year will be my first time planting in one. I've done a lot of research about this (here and on other forums) and it seems most people using earthtainers, earthboxes, or other SWC containers have successfully reused the soil. They top off the old mix with some fresh mix, and then add new lime plus fertilizer. Most people have been doing this for 2-3 seasons and are happy with the results.

Wouldn't a sensible compromise be to change soil and sterilize the container WHEN you've had a problem rather than before? Potting mix isn't cheap. I suppose once in a while you'd have an unexpected failure attributable to not starting fresh, but it'd have to be fairly frequent to justify the financial hit of seasonal replacements. Getting three seasons reduces the cost from $~13 to ~4-5. Not arguing, just considering....

The Earthtainer are based on the Earthbox system. Basically just an upgraded version.
Here are their instructions for winterizing or re-planting.

http://earthbox.com/consumer/gardening-tips.html

I think it is important to maintain a porous growing medium to facilitate proper wicking of the moisture. Over time, the increased root content left in the 'Tainer may negatively impact this wicking action.

My recommendation is to remove the root-ball with as much of the roots left intact with the plant. My process is to scoop out about half a cubic foot of the potting mix per plant, then stir in new mix when replanting. I don't have a science based reason for this process, other than trying to rotate out the old mix in 3 year increments just feels about right.

While I don't agree with the EarthBox Company's recommendation to just cover up the old mix indefinitely reusing it, I'm sure they have done their homework on this.

Raybo

Lowes sells the wire clips loosely for 28-cents each. Home Depot sells them in blister packs for over $2 for 2 of them (yikes!).

What did you use to make your own threads on the cage 'feet'? (just curious)

Some people just rinse the glass out and put it back in the cupboard. Plants are susceptible to pathogens just the same as we are.

And how often is someone made sick from a glass that was just rinsed? Depends on conditions, really. Sometimes the flu may be going around and it could be very easy to catch something that way; other times, nobody will catch any pathogens from the glass. It's probably very similar for tomatoes- if there is more tomato disease in your area, it's better to clean out the tainer every time. If you don't have/haven't had any problems with diseases during the first season, why would it hurt to re-use?

For commercial growers preventative replacement of container soil is sensible; any disease pathogens mean significant loss.
Timmy grows greenhouse tomatoes in buckets & 1 way he protects his investment is total "soil" change.
Home gardeners have leeway to suit their circumstances & trade off in economizing against potential problems.
Aside from cost, personal choice should be made considering losing your tomato crop ( if misjudge seasonal disease risk factor) & the degree of yield(if old substrate degraded significantly).

Thanks for the replies!

To cut the threads (responding to someones inquiry) I used a die cutter, like from a tap and die set like this:
http://www.sears.com/shc/s/p_10153_12605_00952383000P?vName=Tools&cName=Mechanics+Tools&sName=Taps+%26+Dies

Please note I didnt go buy a tap and die set just to finish my tainer cages, I borrowed from the guy who suggested it. And it worked great.
But if I could have found all the wire clips I needed I wouldnt have needed to pick my buddies brain, and down here the clips cost a buck a piece at lowes as well. I WISH they were only 28 cents. Seems each store (home depot, lowes ace) only thought to carry 5-10 clips, not the 78 I wanted/needed.
So the die cut with 2 nuts/washers is also a lot cheaper. Just takes longer.