- Potting Soil - I'm pretty particular about the kind of potting soil I use. Over time I've figured out which ones I like and those that don't work as well. I choose to garden organically, so I try to buy organic potting soil. I'm a huge fan of Coast of Maine Bar Harbor Blend. I also like Organic Mechanics. I'm not as fond of Miracle-Gro Organic soil. It may take some experimentation to find a good brand sold in your area. I like a soil that isn't too chunky-meaning it doesn't have big hunks of bark in it, which is my objection to the Miracle-Gro Organic. I also look for a soil that doesn't have water retaining crystals or fertilizer already added.
- Sun - In my experience, almost everybody overestimates how much direct sun an area gets--sometimes they overestimate by a lot. You really have to time it with a watch over the course of an entire day, close to the time of year that you will be growing. You can also use a sun calculator to get an accurate measure. Full sun means at least 6 hours of direct sun per day and most vegetables will be happier with even more. Another thing to beware of is that trees can grow and start to shade an area where you previously had lots of sun. Make sure to check your exposure every year. That said, if you live in a searingly hot area, it is easy to cook your plants in containers--even those that like sun. You may need to give your pots some shade in the middle of the day.
- Water - Almost all veggies like to be kept at a constant moisture level. This is particularly challenging in containers which tend to dry out really quickly. If you let them get too dry, it can stress your plants and then they won't produce well. Too much water and they tend to keel over dead. To avoid this, you can use a drip irrigation system, self-watering containers or really keep an eye on your soil, testing it by sticking your finger up to the second knuckle and adding water until it flows out of the bottom of your container. In the heat of the summer, or if there is lots of wind, you might even have to water your containers several times a day.
- Fertilizer - When I first started container gardening, I didn't realize that I had to feed my plants. Now I know it is absolutely essential to growing most plants successfully. I add an all purpose, slow release fertilizer to the potting soil, making sure to mix it into the soil throughout the container. I also then use a diluted liquid fertilizer, like fish emulsion and seaweed, about every other week.
- Critters - There are any number of critters who will try to eat your veggies before you have the chance to. Rodents, insects, even dogs can decimate a container full of vegetables in a ridiculously short amount of time. There are all kinds of ways to protect your plants, but first you need to figure out who or what is eating them. Even better, be proactive, before the damage is done and try to figure out who is likely to try to munch your plants. You can use fencing, or try some techniques to scare critters off, like using Mylar tape or hanging CD to frighten the critters. Some people even use plastic snakes and milk jugs painted brown to ward off rodents. I garden organically, so for insects, depending on what kind I'm dealing with, I either pick them off (tomato hornworms), try hosing off the insects (aphids)and if that doesn't work, I go to spraying them with insecticidal soap. If that doesn't work, or I know it won't (lily beetles and spider mites) I spray them with neem oil.
- Pollinators - The vast majority of vegetable plants need pollinators to produce. There are some areas where there are simply not enough bees and insects to pollinate your plants. In that case you have to do it yourself with hand pollination
There are no guarantees in any kind of gardening--Mother Nature makes absolutely sure of that. However, if you take care of the basics, listed above (though I didn't even get into fungus!) your chances of success are pretty good.