garden sulphur. If you are growing in containers then make your own potting mix using peat. The peat in commercial potting mixes doesn't count. Peat is naturally highly acidic (3.5-4.5), but in a commercial potting mix lime is added to raise the ph of the mix. Buying the 2.2 cu ft bags of spaghnum peat in the store gets you the non ph adjusted stuff.

Pine needles are also often lower in ph.

The garden sulphur I mentioned is aluminum sulphate and can be purchased at any well stocked garden center.

However, your observation that rain helped your plants is a good one. I suggest using rainwater for your containers whenever possible. Rain is naturally acidic, and surely you have heard of acid rain? All that means is industrial polutants have made the rain even more acidic than it normally is. ph of 4.5-6 are normal for rain. You say you don't get much rain, but a rainbarrel can store what rain you get assuming you have access to a rain downspout. The barrel is attached to the downspout and catches whatever rainwater is available. Alternately you can do what I do and have a bunch of 5 gallon buckets. When it rains I go stand by the downspout and fill the buckets. A moderate rain allows me to fill a 5 gal bucket in about 1 minute. I need rainwater to grow blueberries and my houseplants seem to prefer it as well.

You might check with your municipality as many have programs to subsidize or even install rainbarrels for free nowadays, especially in areas where potable water is in short supply and water usage restrictions are common.

Good luck.

Included in the carboxylic family of acids is citric acid. It's an organic acid made by fermenting sugar from cane or molasses in the presence of a specific fungus. It works very well as a water acidifier (Monrovia uses it in their production of nursery material) and has an added bonus - it helps nullify the deleterious effects of dissolved metal salts (as in fertilizer). White or cider vinegar would also work well to offset the high pH of your water. In both cases, you would need to experiment to find the correct solution strength.

You would soon discover that trying to manage and maintain the pH of container soils is an exercise in futility. Aluminum sulfate can build up quickly in in situ soils and can be even more problematic in containers. A better choice in chemicals would an elemental sulfur product like Agri-sul or Solu-sul, but for the hobby grower, using water (including rain water, as mentioned) as the vehicle for changing/maintaining a more favorable pH is a choice less fraught with potential problems. If rain water doesn't do the trick, try using a 1 - 2 tsp per gallon solution of vinegar water & see if your plants don't show improvement.

An aside: Most grower's water is much higher in pH than they might suspect and will find that if their water comes from a treatment facility, the pH varies over a surprisingly wide range. Water supplies that come from ground water can be extremely high while that supplied from surface water is generally lower in pH, but of course, it varies by locale. My water happens to come from surface water (Lake Huron) and ranges from around 8.0 on the low side all the way up to near 10.0 on the high side at certain times of the year. A call to your municipal water supplier will get you info on the pH and alkalinity range of your water.

Al