Can I mix old potting dirt with mew or put the old in the bottom of th

Yes as long as the soil is not buggy

I don't, the soil has lost all of its nutrients.

i mix together and add some slow release fertilizer

It is better to replace all the potting soil with new

Sure you can! Most potting soils have fertilizer in them which will diminish over time with use, just fertilize your plants by other methods.

Yes and no...... depends on the plant

How to Reuse Potting Soil Safely | Dengarden

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You could do either. I would use old at bottom of pot.

Yes, fertilize after but, make certain there are no previous molds or growth in the container or soil before reuse.

HI Mary. Every spring I take all of the soil from my pots and mix in new, and then use that for my potting soil.

sorry, when i said stop watering I thought you meant making green tomatoes to ripen.

Never! Old soil is depleted of all of its organic nutrients and is loaded with insoluble residues of minerals and chemicals various kinds that have collected throughout the growing season. Some come from liquid fertiler, most comes from the tap water used to supply moisture. Have you ever noticed strange looking crystals on the top of the soil or on the sides of the pots that looks like table salt? Those are insoluble bad stuff that plants can't use. Buy, or make, new and good potting soil for you potted plants. And, never use gardens soil or dirt from your yard. Only god knows what guck that stuff contains...lots of pollutants more than likely. Don't be cheap. Buy good quality potting soil from a reputable maker. Beware the stuff (cheapest) that is made from composted sludge (from a city sewer system) or manure. It is only good for use in outdoor flower beds when mixed with existing soil.