I want to lay mulch down around my already established plants to help retain moisture and discourage weeds. Is there a recommended material for this? Or at least some materials I should know to avoid?
The choices I'm looking at right now are hardwood, cedar, and cypress (all available from my local Lowes/Home Depot/etc and are pretty cheap. Also, my city has a program that gathers wood that people are throwing away and shreds them into mulch. It's free to take some and they'll fill up the back of your truck for you as many times as you want. You end up with a random collection of wood...not sure if this really matters though.
I know that I should be mulching some of my veggies. But in practice I never have. Here are some alternatives to mulching that have (mostly) worked well for me:
Plant the crops much closer than you normally would. Their own leaves will shade the ground (protecting moisture) and they'll crowd out weeds.
Companion plant a ground cover crop with a taller crop. Two examples: I grow oregano around the base of my peppers, and "three sisters" uses squash as "mulch" for the beans and corn.
You can also use a plain old black trash bag or a tarp or a burlap bag. Some of these materials are water permeable, but some are not. Either way you need to be very diligent about getting water into the soil, because rain will behave differently on these than on bare soil or straw or wood mulch. The upside is that it a black covering will also warm the soil (for the plants that like that sort of thing).
If I was going to pay to buy mulch for a vegetable garden, I wouldn't buy a wood-based product. It's going to be extra work to scrape off the mulch at the end of the season, and I wouldn't want to till 3" of wood into my garden beds. That much wood will take a long time to break down, and while it is decomposing it will steal a lot of nitrogen.
The other problem I've sometimes had with hardwood-based mulches is that they can sprout "interesting" fungus. I have no idea if they're harmful, but I've seen hardwood mulches throw up nasty-looking yellow or blue fungi.
Stay away from the grab-bag mulch. Certain wood types contain chemicals that will be harmful for your vegetables. (E.g. black walnut gives off juglone which can kill your plants.)
I like pine bark for perennial beds, but not as much for annuals.
If straw bales are cheap where you are, that would be a much better bet. Lay down 3" of straw and at the end of the season you can either rototill/chop it into the soil to decompose over winter or you can strip it off and possibly reuse it for a second season. Straw is easier to strip off than wood.
This doesn't help you much with plants that you already have growing, but I've used plastic mulch at the beginning of the season with good results. (I've used both heavy black plastic and the red plastic that is supposed to be good for tomatoes.) First lay out a soaker hose in the beds that are going to have plastic mulch, and then put down the plastic. As a bonus, black plastic absorbs sunlight and helps to warm cool spring soil. Cut slits in the plastic as you put in your transplants. The disadvantages to plastic mulch are:
You've got to get rid of it when the season is done (unless you're careful and then maybe you can get two seasons out of it).
Weeds still pop up in the slits that you cut for the plants. You can't really pull these since they're right next to the plant, cutting them with scissors was what I had to resort to.
Since the plastic will shed rainwater, you've got to be careful about irrigation -- as mentioned above, make sure you get the soaker hose under the mulch when you're preparing the beds. (I found it annoying that I had to water even when we had plenty of rain.)
I don't use plastic now -- except for some leftover very heavy duty sheets that I use to smother weeds out of beds.
Another alternative is cardboard. I experimented this past summer by laying down overlapping sheets in the path between two beds in my vegetable garden and weighted it with rocks. It gave very good weed suppression. The only weed problem I had was that some creeping weeds would "hide" under the edges and sneak out the sides; it was harder to hoe these out since the cardboard was in the way. Don't do this if you care about appearance, it's a bit ugly.
I also tried wet shredded newspaper in the path between two beds. I'd guess it was about 1-2" thick. Didn't work very well -- either I didn't put it down thickly enough, the weeds were too strong, or it's just not effective weed control. It also breaks down much faster than cardboard. It was mostly invisible by the end of the summer (especially since I had to attack weeds which were coming up through it). Good for water retention (which probably partly explains why the weeds were so happy!).
Personally I don't think you can use anything better than good quality compost. It's now the only thing I use as a mulch layer in my garden (not quite 100% true, see below).
Compost will feed the soil and plants slowly (& naturally) over time...
At the end of the growing season the remainder of the compost can easily be dug into the soil without worrying (too much) what's being adding too the soil.
Or if you practice the "No Dig Growing" method of vegetable growing you won't be digging the remainder into the soil, instead you will simply add a fresh layer of compost on top.
The only other mulch material I use in my garden is finely shredded fall leaves. Not quite as good as compost, but if you're having to part with your hard earned cash, finely shredded fall leaves are at least half the cost of compost per cubic yard (metre).
Listed below are a few excellent "mulch" resources (at least I think they are):
For water retention and weed suppression, a thicker layer of mulch is generally better (3" is the rule of thumb I have been using). Since you have access to free recycled mulch, take advantage of that for a thick base layer.
If you want to improve the appearance, lay a thin layer of bark on top -- saves money and look good too. I have used hardwood, cedar, and cypress without any noticeable deleterious effects. Since you say you have a truck, it might be cheaper to buy this mulch in bulk at a nursery.
I use pea straw (from field peas) everywhere up to 7cm (3") deep. It's not necessarily the cheapest source of mulch but definitely cheap enough. The bonus is that little field peas sprout here and there due to the peas left in the straw and so if they're not in direct competition with a weaker plant I let them run their 30cm (1') course and improve the soil by adding nitrogen while doing all the things any other mulch does: retaining moisture, suppressing weeds and discouraging minor erosion over the summer.
Fresh wood mulch is not a good idea for garden mulch for two reasons:
It ties up nitrogen from the soil, negatively impacting it's availability for plants.
It harbors fungi that may be damaging to plants and nearby structures (one common problem with wood mulch is cannon fungi which literally shoot little black balls of tar up to 30 feet away).
There are other problems as well such as chemically treated wood or the natural plant retardent known as juglone that exists in certain trees such as black walnut. If its not wood you are chipping yourself, I would not use it. Chipped wood mulch would actually be on the bottom of my list to use. It would be better off in the compost pile.
There are much better mulch options:
Pine straw. This stuff is cheap and awesome. It will last about two years and will naturally break down into the soil. This is my choice.
Shredded leaves are a great mulch, but better as the main ingredient of a good compost pile. Leaves encourage A LOT of worm traffic.
Newspaper covered with #1 or #2. If you are looking to kill pesky weeds, a few sheets of newsprint covered by pine straw or mulch will do the trick.
Straw (not HAY!!!). Regular old straw works well, but it has gone up in price and is not always clearly labeled as straw. You do NOT want hay as hay includes all of the seed heads alongside the plant stalks which will result in a massive weed invasion if used. Straw breaks down faster than pine straw.
Plastic/fabric mulch. There are a lot of synthetic garden covers now a days that allow you to plant through them and that allow water and air to exchange seemlessly. The downside is expense and they aren't easily applied to large areas without special equipment.
about mulches in a home garden dont spend any money is the rule ....everyone has mulch on their property ....leaves can be used without shredding if the plants are big enough to see sunlight above the leaves.. the plants will stop the wind blowing the leaves away......nothing grows through a thick layer of leaves ...the leaves rot down and become compost.....encourage worms.....and pesky birds kicking over the leaves looking for worms....they are my free roto tillers...but annoying if small seedling are in ....so for small seedlings ...soft topsoil.. then mulch later when they are bigger...a weed that has been pulled.. easy when the soil is soft coz of continual mulching.. is then laid down on top of the mulch with the soil shaken out of the roots...this weed is then free mulch as it rots it becomes compost ..then soil...a continual cycle
plastic should only be used to lay over a area of new ground that has extreme weeds..like ginger ...bamboo...or use a digger...plastic doesent rot down and nourish the soil...free garden waste used as mulch is the one...no driving down to the garden centre to buy wood chips...or plastic...common sense isnt it?
I'm posting this seven years' too late only to let people know that there is an alternative that WORKS. This is cocoa bean hulls. Not only is this mulch relatively cheap, it also smells good when you put it on your garden AND softens your hands while you do it :) Cocoa bean hulls last only one season, so you can easily replant the next year, they build tilth, and they suppress weeds. Now, they aren't perfect. They act as a minor herbicide, so make sure anything you plant has at least four true leaves on it before you mulch it, they can become unsightly for a week or two as a fungus runs through them (it doesn't kill your plants), and they can rot melon/squash fruits, so best not to use in those beds except right near the actual plants. I've built up to 3 inches of beautiful topsoil (from pink clay) over 10 years of cocoa bean mulch; they're especially good for Solanum and beans.