Here's a bunch of answers to questions asked. Remember there are always different opinions, just like an oil thread or how to break in your new bike. For all the soil questions, I personally really like the soil and aggregates at Petrie's out in Milton. Their stuff is slightly more expensive than some other places, but it's very high quality and I really feel you get what you pay for out there. For Toronto area, I have always had great soil and mulch from Speelman's which is just near Rosey Toes at Wendell/Wilson Ave.
FLSTC: Clover is actually good for your lawn, now and for the future, because of all the things that Matthew posted in that link. Having healthy soil under your grass is best, but having a touch of clover is a little better. If you want to get rid of clover because you prefer just having grass, then you could hand pull it little by little, with the aid of a fan rake to help lift it thereby making it easier to pull. You could also fertilize with nitrogen (use corn gluten) because generally speaking, clover dislikes soils that have an abundance of nitrogen, and the clover also tends to show up in soils that are lower in nitrogen. Nitrogen however, is rather mobile in the soil, which means it has a higher tendency to leach out of the soil in heavy rainstorms and enter the wastewater system - if you care about that sort of thing then don't overuse the product while trying to give some extra love to your grass.
nobbie48: Compost is a term used to describe well decomposed organic matter. Fully decomposed organic matter is the ideal end product and is called humus. Compost is excellent as a major component of vegetable beds and can also be used once a year as a lawn topdressing to help enrich the soil. Compost is best if the internal temperature of the compost pile has reached about 60degC, to help kill off any pathogens and weed seeds. Often this is not the case and so compost like I make in my backyard will certainly have weed seeds in it. This year my weeds seeds are tomatoes - hundreds of them popping up everywhere! Compost purchased at a reputable place should have their compost produced in a monitored environment where weeds seeds are properly cooked. There are different types of compost and sometimes they will also have a type of manure mixed in. Read the label or talk to a worker there who knows what they are selling.
Triple mix is a term used to describe a type of soil that typically has 3 main parts to it, which are usually compost, topsoil and either sand or peat moss in varying proportions, depending on where it is processed. There are some who feel that peat is a semi non-renewable resource and should not be mined from peat bogs, because they are delicate ecosystems that have taken thousands of years to form. Triple mix is generally used in garden beds where different plants have different nutrient/moisture needs and the blend of ingredients serves a variety of plants well.
Topsoil is quite literally the soil in the top several inches of the earths surface and should typically have a high nutrient content if it is fresh, because plants have been growing and decomposing in it for a long time. If it has been sitting for a long time in a garden center, that nutrient content may degrade somewhat. There can be weeds in top soil, but usually a quality aggregate/garden center will sell screened soil that is relatively weed free. Top soil is generally great for lawns as a base layer or as a yearly topdressing and if fresh, I would also suggest it for gardens.
Worth noting... another soil term that is commonly used is loam. Loam is part sand, silt and clay at a ratio of 2:2:1. With about 5% organic matter thrown into it, it makes what is generally considered to be the ideal soil which has the perfect balance of drainage, water retention, nutrient content/retention and porosity. That ratio would look something like 38%sand, 38%silt, 19%clay, 5%organic matter.
Joe: Soil that is bagged or bulk may totally vary in quality based on what was put in it to begin with. Furthermore, what one place calls triple mix might be quite different in quality than another place. Same goes for compost and topsoil. I personally like to order my soil/mulch by the cubic yard and have a truck just dump it on my driveway. This way I can just shovel/wheelbarrow it around where I need it and more importantly, I can go to the place it comes from and inspect it to see if I like it or not. I can't do this as well with the bagged stuff, but usually the bagged stuff is fine for small jobs if you are talking about the 30l bags at home depot etc. And yes this same bagged soil is typically cooked to the point that it would be completely weed free. A friend I work with (who received one of the big 'Less Mess' cubic yards of soil for her allotment garden) was telling me that the soil she received does not seem to accept water very well. Sometimes when the soil is cooked to make sure it is weed or pathogen free, the soil seems to get so hot, it then becomes hydrophobic and repels water. I also see this with the city compost that has a tough time properly absorbing water the way a nice soil/compost would - and it also has plastic it in it, but I digress. I'm not totally sure why these soil types get hydrophobic, but I'm guessing it's the cooking process.
Lastly seed sold in bulk is only better in that you can specifically choose the varieties of grass seed you are buying. So if you know areas of your lawn that are shady/moist and another that is sunny/dry and another that is shady/dry etc, you can put down seed for each specific area and make them gradually blend into each other so it doesn't look patchy. If you have a shady area, don't lay sod there, because sod is almost always Kentucky Bluegrass which often has a poor shade tolerance. Sod is excellent for sunny area, but buy shade seed for the shady areas (like Creeping Red Fescue, Hard Fescue, Chewings Fescue), or lay sod to get the instant lawn effect and overseed with shade specific varieties.
TLDR: read that book I posted about earlier.
