Hmm, I have not tried tree and shrub potting mix. I use potting mix that says it is for acidic plants or specifically for azaleas, camellias or hydrangeas. Or better yet, you can make your own potting mix by doing a forum search for the phrase "potting mix".

Ericaceous refers to plants that like acidic soil. These plants are all members of the Ericaceae Family of plants.

Make sure the potted plants do not dry out. A little dry out may be ok but extreme periods of dryness are not good. When extremely dry, you may notice that the soil repels water and that the soil pulls away from the sides of the pot. When the mix gets very dry, it may become hydrophobic and not absorb moisture well. This happens also with regular garden soil.

In those cases, one has to apply water very, very slowly in order for it to start absorbing water again. I have not decided which is worse when dry, some of my clayish dried out soil, caliche dried out soil or peat moss. If your mix has a lot of peat moss and you let it get dry, oh Lord. While it can hold many times its weight in water, peat moss
will just not "cooperate" when you try to add water after it is allowed
to dry out. So use patience. You just have to slowly, slowly, I mean drip slowly try to get it damp before it starts taking moisture again.

I have seen pine bark at the big stores for sale. Some of the smaller local plant nurseries have it in smaller sizes than Lowes' and HD's pine bark.

I use calloways shrub and tree mix. They don't use peat moss. I want aged pine bark or ericaceous compost to help lowering the ph because the water in Arlington is quite alkaline. I left the pot with hardened soil outside and i will check if this constant light shower we are getting will help or not. I have used pine bark mulch but just learned that i could top dress with compost rather than mulch.

If the potting mix does not have peat moss, it sounds like the potting mix got hard because it dried out. Regarding your question about pine bark, if you are in Arlington, Texas, Calloway's also sells pine bark mulch and cedar mulch.

I got pine bark mulch from the plant shed which is cheaper than calloway's. I can't find aged pine bark fine though. I want something that's decomposed or partly decomposed. :(

Locally I have not seen it but I have not been looking for it in a while. I did once, as I wanted to use it for azaleas, which have tiny fibruous roots but, the plants I have used the pine bark medium size on have done great so I finally quit looking for it. Call Redenta's in Arlington and North Haven Gardens in Dallas. Have you considered cedar mulch?

I have been to Redenta's but I did not see pine bark fines. I have heard of North Haven Gardens but I haven't been there. Will check it out. What's the advantage of cedar mulch?

Thanks Luis for all the advice. I just got Calloway's organic compost today. They are all item 30-50% off in the store. It's 100% pine bark so I think it will acidify my hydrangea and keep them blue :)

Oh. You never said you were trying to keep them blue. I thought you were only trying to keep the potting mix acidic. For blues, you will need aluminum. And also an acidic potting mix that will make the shrubs be able to absorb the aluminum.

For those purposes, I find that aluminum sulfate will do a better job keeping them blue as potting mix sometimes has either no or little levels of aluminum. But if your potting mix from Calloway's works, leave things be.

A disadvantage of a/s in this suggestion is that you would have to apply a/s regularly as it leeches due to the frequent waterings that plants get in pots. If the Calloways potting mix provides enough aluminum already then don't bother adding another chore to the list of things to do in the garden. But after a while, the supply of aluminum may be limited and you would notice that when the blues are not as blue as before; then a bit of a/s may help.

Enjoy those blues!

Thanks Luis, I prefer blue hydrangeas but my blue purple Endless Summer turned pink last summer so I bought aluminum sulfate. I will also apply them soon to ensure that the soil is acidic. :)

Hydrangea leaves -specially mac leaves- of shrubs planted on the ground tolerate alkaline soils in this area somewhat. I find that if I amend the soil in Spring with greensand/aluminumsulfate/gardenSulphur, most years I will not need to amend again until the following Spring. However, rainy weather or other conditions will sometimes force me to amend again in July-August. Oakleaf leaves tend to tolerate the alkalinity further.

The last few yeas I have been amending the soil around one unnamed lacecap that was supposed to be a Nikko Blue. The unscientific experiment has yielded purplish-pink blooms. Mind you, I am not attempting purple or blue per se, just trying to see what happens when I apply selected amounts of amendments. Onviously, the more I add, the closer it gets to blue but so far, "closer" is the color purple.