I have a lot of very large pots I want to use this year. Purchasing a good potting mix for so many large containers would be prohibitive so I would like to attempt to make my own potting mix.

I have large bales of medium to coarse Perlite and peat moss. Could I add composted oak leaves to the mix without ruining things? I have a lot of rotted oak leaves that I could use to help bulk up the potting mix but I don't want to waste my purchased ingredients by adding the rotted leaves. I don't plan to grow anything expensive in these pots that cannot be replaced, just need a decent growing medium for the pots.

Myles

@Myles, I see nothing wrong with using fully composted leaves. It will add water-retention to your media, so you need to compensate for this with additional coarse perlite or something like (clean) cypress mulch. You want a well-draining, good aerated media. Keep in mind that peat is acidic. If you are growing acid-loving plants, so much the better. Otherwise, add a couple of cups of lime for every wheelbarrow full of media. If you happen to be using milled sphagnum rather than peat, the sphagnum is neutral, so no lime will be necessary.

@drdawg, thank you so much for taking time to reply and for your helpful advice. I will double check but I believe what I have is peat; if so, will be adding Lime to my shopping list.

Myles

Packing of peat is often in a compressed "bale" whereas milled sphagnum will be bagged and it will be light and fluffy. Packaging has gotten so confusing, since both peat and milled sphagnum will say "Sphagnum Peat Moss". Peat moss does comes from sphagnum but sphagnum is not peat.

Make sure your oak leaves are completely composted. If you can discern parts of leaves in the "final" product, it is not done. Using partially composted leaves is a crap shoot because you don't know how much nitrogen it will eat up to finish composting while it is in your mix. You won't know if you are over or under fertilizing until it's too late. In addition, if the leaves are not full composted, your mix will be constantly shrinking in volume as the season progresses.

I thank you both for this additional information. Excellent to know. Maybe I should just stick with the peat, perlite and the lime and use my rotted leaves as an amendment to my beds. The lower levels of leaves have had several years to rot down but I don't turn the pile so better to be safe than sorry.

Myles

Oak leaves often do take a long time to completely decompose. When they are just in a pile, ample nitrogen is often lacking which slows the decomposition process. But if it is done cooking, there is nothing better than compost for buffering things that could go wrong in soil, like too high or too low pH, or an imbalance of good/bad soil organisms.

If your oak leaves will pass through a 1/2" hardware cloth. they are composted enough to use.

Coppice said:If your oak leaves will pass through a 1/2" hardware cloth. they are composted enough to use.

This info is so helpful. I'd guess 80% of my pile would meet this criteria. Will pick up a piece of half inch hardware cloth and screen some to experiment with in a potted planting. The one thing I have a lot of is Oak leaves. Run the mower over them, dump in a pile and let mother nature take over.

Myles

Yep, that's exactly what I do. My bagging mulching mower does a good job and that's the only time I use the bagger or the mulcher. I just dump the mulched leaves on my compost pile.

One more question, please. Does it matter if I purchase powdered agriculture Lime or Pelleted Lime to use in my home mixed potting mix? Agri Lime comes in 40 lb bags (do I need that much?) or garden Lime (smaller bag) that is in pelleted form?

Myles

Since it is a potting mix, I would use powdered rather than pelleted lime. You want the neutralizing effect to be rapid. I think pelleting of lime is only done so it will spread more easily and uniformly with a mechanical spreader.

And be less dusty.

Maybe pelleted lime falls apart so easily that it might not matter a lot. I never bought pelleted lime: too cheap.

May I add a question? When you-all add lime to a potting mix, do you insist on dolomite lime? Back when I used it on lawns in New England, the "conventional wisdom" was to always use dolomite lime because the Mg it adds was needed, and all-Ca would be undesirable.

But now I've learned that what is "always true" in one region may be "usually false" in some other region.

And pots are not lawns.

RickCorey said:
May I add a question? When you-all add lime to a potting mix, do you insist on dolomite lime? Back when I used it on lawns in New England, the "conventional wisdom" was to always use dolomite lime because the Mg it adds was needed, and all-Ca would be undesirable.

In most cases dolomitic lime would be used in a soilless potting mix to do exactly what you say, supply both calcium and magnesium. Both are essential secondary macronutrients but are not usually included in fertilizers. Some fertilizers do contain magnesium but one would have to check the label to make sure because I think most don't. Another option if not using dolomitic lime but where magnesium is not naturally in the potting mix ingredients would be Epsom salts (magnesium sulfate) but dolomitic lime would be a longer term solution.

The media pH in a soilless mix can actually safely be a bit lower than in mineral garden soil. Whether you need to supply both calcium and magnesium when adding to garden soil would depend on a soil test, but too high a level of calcium (or potassium) can result in less magnesium for the plants.

Do you get your potting mix tested or do you just "guess-timate" on what to add? If you test your mix, where do you get it done?

I have made my own potting soils/orchid media for so long, it is all second-nature to me. When you see great growth along with great draining, you can be reasonably sure that the mix is a good one. I don't use a bit of peat, so acidity is of no concern to me.

Thanks, Sue.