Considering the chancey way home concocted planting soil might behave, I just don't think its worth the bother.
Aside from how you evidently have had bad luck with a Scott's formulae for potting soil, I still think the people who know plants can best make the soil to suit.

But if you wish to try a formulae that a Sunset Book suggests:
blend equal amounts of coarse sand (buy it at any building supply dealer or quarry) and garden topsoil (or loam) abd peat moss.
To each quart of this mix, add 1/2 cup each charcoal and perlite, leaf mould or fir bark.

Every ingredient has a purpose. Garden loam or topssoil, contains particles of clay that hold fertilizing materials in an available state for plant roots.
Sand, perlite and leaf mould hold air around the roots which is essential for good plant growth.
The leaf mould provides some nutrients.
Charcoal bits keep the soil 'sweet'.

Most nurseries and garden centres have these materials available.
Garden soil --if used--must be sterilized since it may contain pests, disease and weed seeds.

Sterilizing such in a home oven is not a very nice way to treat the kitchen air. It makes for a very nasty odour.

I agree about some potting soils that are available in some stores. Mostly clay, they turn to rock when given moisture.
These types are usually the "on sale"....or "special" items at very reduced prices. You end up paying for it when your plants cant obtain proper watering and feeding.

I've found that if you look around in places like Home Depot, the bag you might consider for your plants has one ....maybe even two...bags that have been holed and their contents clearly leaking out.
By putting some into your hands and squeezing it, it might give a better idea what the ingredients of the bag contains.
Generally, if the soil falls easily through your fingers...it is not a good soil.
If it forms a ball before crumbling, it contains sufficient ingredients to hold moisture.

I usually mix a cheap potting soil (not hyponex) half and half with perlite for normal plants. I have also added aquatic soil to my mix, it's expensive but you don't have to swap out as often. Turface or other high fire clay soil ammendments work well also. Since I like my soil to be fast draining and fungus gnat free, I tend to shy away from organics and peat to much which breaks down too quickly and makes a mess. I also shy away from anything which might hold moisture too long.

What kind of plants are you planting, this will help us to give the right types of soil mixture.

I agree wholeheartedly with Mentha. We need to know what you're growing to give you best advise, but cheap potting soil and perlite is a good general mix. The last few years I've had trouble finding what I like as perlite--most of it is too fine. I order some that's really a little coarser than I prefer, but large is better than small. I think Al said your drainage is only as good as the smallest particles in your mix, and it seems like most the perlite readily available is sugar-fine. I used to mix my own, and used just a basic Cornell mix of equal parts sphagnum peat moss, vermiculite, and perlite (heavier on perlite here with our humidity) and that's not really much more bother than mixing a potting soil and perlite--if you can find good quality ingredients. Using garden loam if you have good loam might be acceptable, but our heavy clay would mean instant death. Organics like leaf mold and compost aren't really desirable in pots since there aren't the natural soil bacteria and other small friends we encourage in the garden--save that lovely stuff for outdoors!

If you are near an OSH they sell large particle perlite in 2-4 CF bags for about $13. I have one which has lasted about 6 months. I'll have to get another bag when I repot everything come spring.

mentha and greenelbows have given you some good advice! Most decent quality potting mixes are soil-less (meaning that they are peat based)but can be greatly improved by adding a high percentage of perlite and Turface. That will make your potting mix highly porous, which is ideal for containerized plants. Avoid vermiculite, which tends to collapse in a very short time.

My own mix is composed of perlite, Turface, and conifer bark fines....no peat at all. Avoid amendments like compost and sand which tend to fill in the large pore spaces.

Thanks everyone! I have a broad mix of plants (two hibiscus, a fittonia, a cordyline, an aglaonema), but the ones that I think could use better drainage are an episcia "Alice's Aussie" and a breynia disticha nana. Everything else is thriving.

If I just refrain from watering until the soil dries out thoroughly, they seem to be okay, but in winter that can take a couple of weeks, and I feel that's far too long.

Maybe the problem is the perlite I'm buying is too fine, as greenelbows mentions. Mentha--I am near an OSH, so I'll definitely get the perlite there. I'll also look into Turface. And what's aquatic soil?

Matt

Aquatic soil is a high fired clay much like Turface, only larger particles, about the same size as cheap cat litter. It is sold for aquatic plants or aqua-scaping (planted aquariums) It is more expensive than turface, but usually easier to find. I found my aquatic soil at the local Farm Supply. I have yet to find a local supplier of Turface.

If your OSH doesn't have the perlite, they can order it for you. The OSH in Paso Robles carries it pretty regularly. It comes in a huge mint-green or yellow-tannish cube bag which looks like the old "generic" label. (Not sure which is which, but one color is vermiculite, the other is perlite)

From your list, I'd say they each could benefit from some lightening of the soil. When plants get larger, as your hibiscus and others will, they tend to hold moisture in the recesses of their plastic pots, so when the top could have a crust the rest could be a soppy sludge.

Sometimes when I have an exceptionally large plant which needs a heavy pot to stand up, I add a layer of perlite on the bottom of the pot. I put the root ball on top of the perlite, then a layer of 90 perlite /10 soil, graduating to a 75/25 mix of whatever soil components I choose to perlite on top, using less perlite with each layer. I know some say not to do this, but I've found few ill effects if it's done gradually in about 4-5 layers. The perlite is less likely to float to the top if the soil is on top of it also, and the problem of dry on top, wet on the bottom is also reduced.

Hi Mentha,

Here is a website for (Lesco.com) for Turface, if you type in your zipcode in the box, ( not sure what part of CA you live), but maybe you can find a supplier near your area. Sorry you will have to copy and paste, I don't know how to post so that you can directly click on it, )o: Good Luck!

http://www.lesco.com/Default.aspx?PageID=26&Category=25&Group=045&Type=059&Form=1255

Matt, don't feel alone..I too use whatever soil is avaible, but add other ingredients..mainly Perlite and Builder's sand. (Peat, depending on the plant I'm repotting.) The mix dries well, maybe too well, since soil dries quickly..the air in my house is fairly moist, so lack of humidity doesn't have anything to do with how fast plants need watering.
Instead of paying 5.99+ for brand name soils, I usually buy what's simply called, Potting Soil for house plants. 25 lbs for 1.99-2.50 in summer. It isn't that I'm Mr. Scrooge, but w/over 300 plants, and since I'm not Bill Gates either, I make do with what I consider appropriate and at the same time, economical.
Miracle Gro sells a few types of soil I deem approrpriate, but they also sell soils that's mainly peat.
And this new soil, the type that is made to reduce watering time, is out of the question.
So, whatever works for you, (it takes experimenting) is the type to use. Toni

Al,
You need to write a book for us soil-adept-less peoples :) I always enjoy reading your posts.

Depending on the plant I either add Perlite or Peat moss to regular potting soil. I use either Pro-Mix or Miracle grow. For instance, Piece lilies like to stay moist at all times so I add a handful or 2 or peat moss to it's soil. Sheffs or other plants that like to dry out a bit between waterings get a little extra Perlite.

Tapla, I was under the impression that pine bark retains water as opposed to draining it

Water retention within particles like pine bark isn't the water retention you need to be concerned about. It's the water that occupies the voids between soil particles that causes the root function/health issues. It you picture a container full of saturated peat, you can 'see' all the water retained between soil particles. That doesn't happen in soils with particles larger than .1 ".

Al