I am sure there are smarter people than I, but I am reusing the dirt out of my old containers, but adding blood meal, bone meal and compost, plus horse manure in the bottom of the containers. I dig out the old plant material first and then remix. I don't think I would add new fertilizer until I noted how the new plants were doing. If you are just planting seeds, I always sprinkle some seed starting mix on the top and then add the seeds in that mixture. This may not be the correct way to do it, but it is my way. Barb

Barb has good comments about how to revitalize a soil mix and about seedlings and fertilizer need, but at the same time, many of these fertilizers are also good if you can mix it in to the soil, compared to top dressing or putting in the first few inches of soil, if you can get in and around the seedling.

Besides a similar regimen as mentioned above, I would add new Osmocote since those granules were being expended even if there were no plants in the containers using them (for example, over the late fall and winter months).

Depending on how rich your compost is, you may not need or want the other components.

My question is I know I'll have to new amendments to it; however my question is since there is existing fertilizer (even though it's probably dead) will I be over fertilizing by amending with adding new fertilizer to old soil that I"m reusing.

In theory a time release fertilizer is two things, something inert which binds the nutrients, and the nutrients themselves. Over time the binding breaks down, freeing the nutrients. They would largely be used by plants or washed away by watering.

If these are older, well watered, containers the active part should be gone, with maybe just the "husk" of binder remaining.

So the old time release fertilizer, well beyond its claimed life, can be ignored.

I do reuse potting soil, and doing so for a year or 2 is fine IME. I add compost and a mix of blood meal, green sand and rock phosphate. I do find after several years that the organic matter in the potting soil breaks down and the texture becomes too fine and compacts, so IME I do have to limit the number of reuses or else add a fair amount of a coarse-textured organic material so that the soil drains well and is good for root growth. I haven't had any issues with diseases, etc. and one benefit of reuse is that I sometimes get volunteer ornamentals from the previous year.

As a test, nhbabs, you might try "sharp" or "builder's" sand when the mix is fine. As always, try a pot or two, before going whole hog.

My roughly 3-1-1 woody compost, sand, soil mix actually drains faster than the store bought mix I have for comparison (EarthGro).

Update: I consider this an OK large outdoor container mix, and would go soil-less for smaller or indoor pots.

This post was edited by johns.coastal.patio on Sat, May 10, 14 at 9:45

Sand is added to container media in order to have more even wetting and increased water retention. I don't see why you would add it to container media that is broken down.

Well, "Sand adds air space to a potting mix," according to the reference attached. I would think those air spaces are the path for drainage. Where else?

Here is a link that might be useful: IFAS Homemade Potting Mix

Sand migrates and compacts very readily and lodges between larger particles, impeding drainage and reducing aeration. In a raised bed or garden/yard, sand functions much differently.

Josh

Well, I have cited half a dozen university extension services by now. I am comfortable with those. Your mileage my vary.

Update: added a last week's photo. I expect those plants to be taller than I am when I get home Monday (6 foot). I think that's pretty good for May, especially given that the season runs through September. Given that it is hard for me to believe that my methods "can't" work.

But I am certainly not a One True anything kind of guy.

You may have something different that works for you.

This post was edited by johns.coastal.patio on Sun, May 11, 14 at 10:26

potting media.. is a water management system ...

you choose the media based on what you are growing in it...

high peat media... is for plants that like a lot of retained moisture ... like annuals.. perennial.. houseplants etc ...

a low peat media with big chunks of other things .. is for plants that prefer a sip of water.. and then high drainage ... such as trees, conifers. shrubs, cacti .... etc ...

a media is wearing out ... when it is no longer performing to expectations as to how the water flows thru it ...

one might analogize.. that when the peat is returning to bog state by breaking down ... your plants suffer.. for lack of proper watering .... either too much for lack of draining... or too little for lack of wetting the whole .... running down the sides and leaving the center bone dry ...

its not really a schedule thing.. nor something you MUST do every year ... its all about observation and understanding ... renewing you media.. as you note its decline ...

if the water runs properly thru the media... then time release ferts can be applied on the top ... and the fert will be properly carried thru the media ... as there should be no need to incorporate it into the media ...

you guys use a lot of fert/amendments compared to me ... but i dont keep things in pots for a long time... one concern with high usage.. is salt accumulations ... salts being ferts ... so you have to throw that into the equation.. of when a media need be changed ... if the media is working properly.. and water flows out the bottom.. as you put it in the top ... then in theory.. you should be washing away a lot of the salts ... and need to replace the nutrients ...

but when your media starts failing.. and your not washing the salts thru... it builds.. and can affect the plants themselves .... such a vicious circle.. eh???

i hope understanding such.. will help you better decide .... how to manage your media ... you shouldnt change it.. simply for the sake of spending money and changing it.. according to someone elses observations in their pots ...

is your media working.. or not .. that is the key ...

ken

John, you may have cited a university extension, but since they said you can use mineral soil in containers they indicted themselves completely. Sand will increase drainage if you go against decades of container nursery research and use mineral soil in containers but only because sand and silt are sooo much finer. I don't know a single grower (actually I know one and their stock is crap) that uses mineral soil in containers. They all use soilless mixes, and use sand to increase wetting and moisture retention. You might want to read "Plant production in containers" by Whitcomb as it is a standard text for the industry.

The important bit in the link.
"A common misconception is that sand improves drainage. When using bark as the primary component, adding sand will decrease drainage. Small sand particles settle between large bark particles, thus decreasing pore space and drainage."

Now if your medium is total muck, I suppose sand will increase drainage. However it won't increase drainage any more than 100% sand. If you have ever tried to grow anything in 100% sand you know it holds way too much water and way too little air. You get tiny, weak hairlike roots and anemic growth.

Here is a link that might be useful: Physical properties of container media

This post was edited by nil13 on Sun, May 11, 14 at 11:40

John, it should also be noted that growers can get away with a much heavier potting mix in a zone 9b than a zone 7b or 5b.

Josh

I think we have reached a "who are you going to believe, me or your lying eyes" situation.

I like what ken said. I will also add that when talking about changing media, a year is different in different places. I can't get away with going 2 years between changes on my media. However, that has a lot do do with the fact that I am in L.A. with a very warm 12mo. growing season. Now compared to where I grew up in Ohio and their 5 month growing season, I have 2 seasons of decomp every year. If I went 2 years I would have 4 seasons of decomp and would really have some serious muck and containers that are only about 1/3 full of media.