Ok, yeah I know a lot of people have tried buckets and failed for various reasons. No offense intended, but that's not the fault of the bucket. It's important to remember that a bucket full of dirt isn't the same as the ground. It has strengths and weaknesses compared to planting directly in the ground, and if we know what some of these are we can actually use buckets to our advantage, whether we have a 1/4 acre garden or an apartment patio.
What to plant?
Well, that's really the big question, isn't it? Not all plants are well-suited to containers. Sweet corn, for example. I suppose you could do it, but there are more reasons this idea will fail than will succeed. Potatoes are another idea that sounds great but doesn't work very well. In a sense, potatoes do work in containers, but only much larger ones such as large trash cans and the various forms of potato towers. Since we can't really make an all-inclusive list of what does and doesn't work well in containers, particularly 5 gallon buckets and other things we tend to have easily available, I'm going to lay out some basic factors and guidelines that I use when considering something for a container.
Size - Generally, nothing larger than a determinate tomato plant will thrive in a 5 gallon bucket. There are some exceptions to this, as I've seen lemon trees and other things growing in them, but generally, nothing bigger than an average tomato plant.
Root penetration - Obviously, a bucket is a limited space in which to grow. This goes hand in hand with plant size, although there are some plants that just can't make it in such a limited space. This is more of an issue with perennials as they are more and more likely to become rootbound the older they get.
Moisture requirements - Maintaining adequate soil moisture is harder in a bucket than in the ground. Generally, you combat this issue by simply watering more often. For some plants, however, this still isn't enough. Especially for plants that require consistent soil moisture. Plants that can't tolerate even slight drying will have problems. I don't think I would try to grow something like celery, and even many herbs and greens will have problems if you forget to water for a day. Even lettuce. Yep. I've forgot a pot of lettuce before, followed by a 90 degree windy day and it's wilted down to the ground by mid afternoon the next day. There are things we can do about this, though, which I'll address later.
Soil temperature requirements - The soil temp in a bucket will be much higher than in the ground, and though there are things we can do about this too, the options are limited. Personally, the only issue I've seen as a result of this is general stress on plants, as well as some tendency for tomatoes to drop blossoms. Generally, though, this is a manageable issue for most garden plants. In some cases, it's a huge advantage.
So where does that leave us? Well, honestly, most things can be grown with at least some success in buckets or similar containers. Keep these factors in mind when choosing plants, and you can then find ways to deal with the disadvantages of buckets for each plant. Or you can just keep reading...
Choosing Containers
Size - My rule of thumb is that the width of the container should be at least half of the recommended plant spacing for any given plant, and the height of the container should be about 1/2 the mature height of the plant. Remember, you aren't going to fill the bucket all the way to the top, so the depth of the soil mix in the container should meet this requirement. Obviously this doesn't always hold true, but generally it will at least be close. As an example, if your tomato plant says 24 inch spacing, then a bucket is about right. When you get into large indeterminate varieties like Brandywine and Amish Paste, these do better with a spacing closer to 30 inches. I have successfully grown both in buckets, with reduced yields vs what they would have seen in the ground. I'm not saying it's not worth it, just know what you're getting into if you plant a Brandywine in a bucket.
Applying this, we get that things like tomatoes go in 5 gallon buckets, peppers go in 2-3 gallon containers, greens can go in just about anything that's at least reasonable, and many herbs can be planted in large coffee cans. I like to stick with buckets, so this usually means I grow two pepper plants in a 5 gallon bucket, although I'll plant in just about anything. I've used old litter boxes, old glass coffee pots, those tubs that Legos come in, and whatever else I can think of. Just stick to the basic size recommendations and you'll have some level of success.
Color - White. Unless you live in an area that is perpetually cold, overcast, etc, white is the best color. There are exceptions to this, but in most cases, I use white buckets or some other light colored container. I wouldn't say don't use dark colored buckets, but know ahead of time that they are going to get very, very hot if the sun beats on them in August. NOTE: Color won't matter if you're using wood containers.
Material - With the exception of building your own wooden containers, plastic is the best. A lot of people talk about using food grade plastic, but my opinion is that there's no need for this. The amount of any chemical that is going to leech from a plastic bucket into even a carrot is likely very, very small. Obviously things that have previously had toxic chemicals in them are out - no old diesel tanks or metal paint thinner cans. No treated lumber or similar materials. Not so much because you might get sick, but because your plants won't thrive. Use your head on this one, and if in doubt don't use it. I'm also going to take a moment to talk about tires. I've written bits about this before, so I won't go deep into it. Don't use tires. Under no circumstances short of starvation would I suggest using tires. If you want to read more about my very strong opinion on that matter, you can go here: Old Tires as Garden Containers?
Shape - Watcha got? Just about any shape container has a use, somewhere.
Media - What to fill them with?
Oh, I suppose you could just dig up some of your soil and use that. I've done it. It kind of works. You can do a lot better though. One of the issues with planting in containers is that there is a limited amount of nutrients in that container. If your soil isn't great, you're going to handicap your plants right from the start. Especially if the container tends to be a bit smaller than it should be. Lots of people will tell you to go buy potting mix or potting soil or composted horse manure or something else like that. You really don't need to, although you do need to do something to both lighten the soil and add nutrients. My method for doing both of these is to add finished compost. My container mix is 1/2 soil and 1/2 finished compost. I also side dress the plants at least once per summer (preferably several times) with another cup or so of finished compost. My finished compost contains considerable amount of composted chicken manure, so it's pretty rich compost. If yours isn't, or if you don't have any at all, go buy a bag from your local garden shop. I hate suggesting anyone buy anything, but you'll be glad you did if you have no other source of good compost.
I'm going to point out here that there is a specific reason that we want to lighten the soil, aside from simply allowing roots to grow better. Containers dry out faster than soil, therefore we water them more often. The more we water, the worse the soil compacts. If you just use soil, by the end of the year, it will be harder than the soil under your walking paths in your garden. When soil is that compacted, it doesn't matter how much you water, the water doesn't penetrate and nothing grows. It's MORE important that we maintain a workable porous soil in a container than it is when planting in the ground. This leads us to some other things worth mentioning.
Properties of planting containers
It's time we go over the nature of the "container ecosystem" if you will, and discuss how the characteristics inherent to growing something in a container can be both strengths and weaknesses.
Soil temperature will almost always be higher, during the growing season. We generally see this as a stressing factor on plants, and generally that is true. We can deal with this in a few ways, but the simplest is to shade the buckets. Don't shade the plants, just the buckets. For me this means that I line up all my buckets north to south, and I have a couple 24 inch wide lengths of plywood that I lean up against the west side of the buckets. Aside from just keeping the sun off the container, this creates a cool area behind the board, allowing heat to dissipate from the containers. You can also accomplish this by grouping your containers, using each of them to shade each other.
This elevated soil temperature can also be a big advantage, especially early in the season. My container plants almost always grow faster than the same varieties planted in the ground, through the months of April and May. I live in zone 4, and many years we don't get the kind of heat necessary to grow nice peppers. I plant many peppers in containers, and then set them along the west side of my house. The heat radiating off the side of the house warms the soil leading to much, much better growth than my peppers planted in the ground. In fact, last year, almost all of my pepper harvest came from those in containers even though I had twice as many pepper plants in the ground. It just wasn't warm enough for peppers to produce well last summer.
It's important to add some kind of fertilizer throughout the growing season. As mentioned earlier, containers have a limited amount of nutrients in them. In the soil, plants can send roots out laterally and vertically looking for moisture and nutrients. This isn't the case in a container, and the soil mixture in a container can become nutrient deficient rather easily even if you start out with a rich compost mixture in the spring. My method to combat this is to add either finished compost or composted chicken manure as a side dressing several times through the growing season. You could use any other fertilizer as well.
We've already discussed watering, but it's worth going a little further. Containers lose moisture faster than the soil for various reasons, so plan to water your containers every day during most of the year, and even twice per day during the hottest parts of the growing season. Anything you can do to automate this process will help considerably. I've seen watering globes used with success, although drip irrigation would be even better. Whenever possible, you should have a catch pan under your containers. Later in the season when plants have deep roots you can simply bottom water. This has the advantage of compacting the soil mixture less, also.
If you do experience soil compaction in your containers, do something about it. The first thing I usually notice when this happens is that the water runs down the sides of the container and right out the bottom, never penetrating the soil. I know most people will cringe at the thought, but if this happens, take a small stake and make some holes around the plant for water to soak into. I use a length of 3/8 rebar for this. Loosen the soil as much as you can without damaging the plant and its roots. Even add more soil around the inside edge of the container to keep water from running down the sides. Whatever you can do to make the water soak into all of the soil mixture in the container. Starting with a good soil mixture is really the best way to prevent this problem, though.
Preparing containers
Whatever container you choose, it needs to have some drain holes. If it doesn't already, drill a few 1/4 inch holes in the bottom of it. Slightly larger holes work too, although once you approach 1/2 inch, that's too big, soil will wash right through those holes. I use 1/4 inch holes because if I want, I can still use the bucket for chicken feed or something else, just by putting a little duct tape over the holes. For a 5 gallon bucket, you're going to need at least 4 holes, and probably more like 6 or 8. I like to place these holes generally in the center of the container rather than around the edges. Water should drain freely, and too few holes means that they could become plugged. Inevitably, there will be a heavy rain or two throughout the summer that will fill your containers right up to the top with water. This should drain within 15-30 minutes or so. If it doesn't, you have too few drain holes in that container.
Containers should be clean, at a minimum spray them out with a hose, and if you aren't sure just what was in them last, scrub them out with some soap and a brush before rinsing.
Add soil mixture as described before. 1/2 good soil and 1/2 finished compost, pre-mixed in another container. If you prefer, yes you can use commercial potting mixtures or make your own mixture. I use dirt and compost because it's readily available and works well for me. Containers should be filled at least 3/4 full, regardless of what you're putting in them. Initially, they should be more full than your goal, because the mixture is going to settle some. I will usually fill the container and then water it well to see where it will settle to, and then plant into the wet mixture. This also helps make sure you don't wash your seeds away when you plant. Under filled containers shade small plants and create a mini-greenhouse climate that can be way too hot for plants in the heat of the summer. For me, 3/4 full is perfect for a 5 gallon bucket. This allows me to put saran wrap or similar plastic over them to retain moisture and heat for very small plants early in the year, too.
You're ready to plant! I direct seed most plants, or you can transplant too. Direct seeds, I cover with plastic to keep the soil moist for the first few days until germination. If you direct seed, plant a few extra seeds, just in case. Transplants and small plants will benefit from being in a container as the lip of the container shields them somewhat from the wind, vs being planted in the ground.
The rest of the growing season
One of the best things about container gardening is you have FAR less weeding to do. Last summer I had about 40 containers, and I was able to weed all of them in 10 minutes a week.
Have I mentioned yet that you need to be diligent with watering? At least check the soil every single day. If you have to leave your plants for a few days, make sure the containers are shaded somehow and soak them really well before leaving.
Supporting plants, especially tomatoes, can be interesting in containers. Typically, I use a stake to support the main stem, although in a large enough container a cage is certainly an option.
Many plants grown in containers will not yield as well as they would in the ground, this is especially true of larger plants. This doesn't mean you shouldn't plant them, just know ahead of time that you might want two plants instead of one.
Summary
Growing in containers brings some challenges to gardening, as well as some advantages. Understanding what you're getting into will help increase your chances of success dramatically.
