Hi, Personally I wouldn't do it. IMO, second year 511 is super for tomatoes all by itself. Mine grew better the 2nd year in the partially composted mix. I didn't add anything except 1/2 the amount of lime, but probably could have skipped it. You might freshen up last years mix with additional pine bark and a little perlite. Not sure why you want to add MG mix to it. What are your concerns. I'm using MG water soluble fertilizer also.

Yes you can, and in the short run 5-1-1 in may actually perfom better than the Gritty mix. But it will wear out quicker (break down) than the gritty mix. I tend to think of annuals going in the 5-1-1 mix, and perinnials in gritty mix. If you are going to be up-potting in a couple of years go with what you have. Either are a better choice than most anything you can find in most garden centers. Gritty mix makes future repots a dream, tip the pot over and you have bare roots.. Grading the pine bark is not fun, I hate it! A major concept of the gritty mix is based on particle size, larger particles have less surface area (by volume) and thus less water retention. 1/4 to 1/8 inch seems to be the optimal size, although due the screening process of pine bark and the thin strips I will let most 1/2 and under get in the mix (under 1/8 is not good either). If you are looking for Turface MVP check a local irrigation supply house, the stuff was designed for baseball diamonds so look in that direction. The dust is not good for the mix (particle size) The gran-i-grit is intended for chickens to help them digest grains. There are many other products other than gran-i-grit that will perform just as well. Look to a local farm supply house for the rock. Rock dust is not good for the mix (particle size) Gypsum is available at the big box home improvements stores. Gritty does dry out quicker than potting soil so you do need to water a bit more often. It is extremely difficult to overwater with gritty mix, that includes mother nature overwatering. Root rot is probably the number one killer of potted plants. After water, air is the most important thing you can give roots (most plants), more important than fertilizer. Gritty mix excels at this without drying out the root system. Gritty mix is heavy stuff, an advantage of heavy is the pot is less likely to tip from heavy winds. Al is a smart guy, it is such a simple concept.

Here's some info about dolomite. It is from a master class in agriculture. Just remember you add lime, then foliage pro, better watch what you do. To much of a good thing can be just as bad. ---------------------------------------- High-magnesium lime Dolomite, or high-magnesium lime, can cause problems too. When dolomite is applied in too large of a quantity it can cause an excess in magnesium and have a negative effect on yields. The problem is it can be as long as three years after the excess lime has been applied before seeing the greatest amount of potential damage to the crop yields. By this time, unless the grower has kept good records, a connection between the liming and declining yields may be overlooked. (A moral here is to keep good records of when, where, how much and what type of lime each field receives.) Have you applied dolomite lime on any of your fields in the last few years? If so, count three crop years from the time of application and check the yields that year and thereafter as compared to yields prior to liming. Even if the applied magnesium from dolomite lime will have a detrimental effect, do not expect to see that yields have dropped the first year. For example, when too much dolomite is applied to land for cotton, it can eventually cause the plant to send out two lesser roots instead of one longer taproot. These roots do not go straight down, but curve to one side instead, and have less depth than the one taproot would normally have. (If you rip and hip, this effect will not always be as evident.) It will take three years to see the full negative effects of overusing dolomitic limestone. But when overused, once those effects have come into full effect it can cost a cotton farmer about ¾ bale of cotton per acre, every year, until the problem is corrected!Excess magnesium costs money In corn, on medium to heavy soils, a high level of magnesium (15%+) costs the farmer 10 bushels of corn per acre. Above 20% magnesium on the soil test reduces the yield by another 5+ bushels per acre. In addition, it will require more nitrogen to produce each bushel of corn every year until the problem is corrected. In legumes, taking soybeans as an example, 13-14% magnesium levels can cause 10 bushels per acre loss per year, even when all other nutrients are present in the proper amounts. Be sure what your soil really needs Even though too much, or the wrong type of lime can cut yields, limestone should always be applied where shown to be needed. Applying the proper amount of lime in the right form can provide far greater increases in yield than the losses that occur from misuse. Have your yields suffered in certain fields in the past few years? If so, avoid the mistake of failing to correctly check for and properly apply any lime that is needed. Just be sure that you use enough to correct the problem, but not so much that it causes problems three years from now and several years thereafter. If there is a need for lime, autumn is the best time to spread it for next Spring's crops. Do it correctly as needed and see the difference liming can make for crops over the next several years.

I'd just flush it thoroughly by pouring a volume of water = to the container volume through it 5-10 times. That should do the trick. I wouldn't plant in it w/o flushing it. Al