I'm trying to plant some vegetables in my second floor balcony. I have one container for each plant. Is this the best method or should I go for one long common container to plant all of them? What are the advantages and disadvantages?
Overall, I think separate containers is an advantage over a common container in your case: a light hobbyist grower.
I can think of 3 advantages to a common container for you:
- Space and soil savings.
- Plant flavor pairing (tomato in the same soil as basil).
- Natural pest-control pairing (onions next to squash to drive away borers).
For separate containers:
- Easier to isolate infested plants.
- Easier to move plants around balcony for different sunlight requirements.
- Easier to meet watering, fertilizer, drainage, and other growing conditions of plants with conflicting requirements.
Edit: I thought you were talking about for starting plants--not planting them in their final destination. So, keep that in mind with my answer. See the edit at the bottom of my answer for stuff more specific to your situation.
I have a fair bit of experience starting members of the solanaceae family in one common pot (not necessarily a larger one than I use for single plants, since I tend to use larger-than-normal pots for those). So, I can enumerate advantages and disadvantages of that method, for those plants.
First, the disadvantages of using one container for multiple solanaceae plants:
- If your plants get a disease, it may spread between them quicker. A lot of people think this contributes to damping off. While I haven't noticed it affecting that, particularly, I have noticed that it seems to make conditions more advantageous for such as what I think is downy mildew.
- The plants won't grow as large as fast.
- Plants near the edges may uproot easily after a while, depending on how they're growing.
- You'll have to split the roots up eventually and/or take cuttings.
- A few of the plants will likely be smaller than the others, or one or more will likely be larger. Sometimes, they're all the same size. I just mean to say that often, some plants will dominate the pot.
- People might think you're crazy or ignorant, because this is commonly advised against by experienced gardeners (mainly for the risk of damping off, as far as I can tell).
- The plants may get rootbound faster. So, use enough soil for how long they need to be in the same pot.
Second, the advantages of lots of solanaceae plants in one pot:
- It saves a lot of space.
- The plants are smaller when they mature, but if you split them up, afterward, they can grow huge fast. One plant in a pot tends to take up a lot more vertical space than several plants in a pot.
- Less stem between leaf nodes. This is nice because stems can take a lot of space. So, you can get more leaf nodes in a space this way, and potentially more flowers in a given space. However, you'll need to give it the right nutrients for what you want.
- You don't need as many containers or as much soil.
- Tomatoes and tomatillos seem to split up fairly easily for transplanting. Don't do it until the stems are thicker. If they have root nodules on the stems, it's usually safe to split them up. Peppers might be stunted after splitting up, but if you give them a lot of light a couple days after the transplant, it'll probably help them to adapt. If you give them a lot of light right away, it could be bad since plants with disturbed roots can wither on too much light. I haven't tried splitting up eggplant and ground cherries, yet.
Anyway, it's not for everyone, but there are reasons some might want to do it. The mildew risk seems higher if you have a humid, warm environment with lots of pots of lots of plants. Dim light would also contribute a lot, but my growing area is fairly bright. Wet leaves also can contribute.
As for cucurbits, you should probably only consider cucumbers for this, if any cucurbits at all, and not more than two or three per pot. It's important to know that cucumbers can grow roots at the leaf nodes fairly easily. You can take cuttings of them. Other cucurbits that will root at the nodes might be considerations, too, but I wouldn't count on it.
All in all, most people wouldn't recommend it, I'm thinking, and it's perhaps riskier, but I personally enjoy it at times. These same advantages and disadvantages won't apply to every kind of plant, nor to every person's growing conditions.
Edit: If you're not going to be transplanting your plants, if they're solanaceae plants, even if you have a large pot, if the plants are closer together, they may still be smaller than normal, and they may be less productive. One plant will still likely dominate. This seems to be the case with tomatoes planted in the same spot in a raised bed, anyhow. I would recommend one plant per pot, for outdoor solanaceae plants. For others, it depends.