When I first started gardening I rarely had much of a garden, or one for very long. I grew many different plants in pots, mainly because I was moving frequently and wanted to keep them with me. I grew a great many herbs, quite a few vegetables and some odd house plants. (I've always sown seeds of strange fruits to see what I can grow). When I went travelling abroad they needed watering but at least they were portable so could stay with friends for the duration.
Once I started my first 'real' garden and gained the luxury of having properly worked soil I became impressed with how well plants grew in the ground compared to the same growing in a container. I could hardly believe it, the plant in the ground always seemed healthier, got bigger, held larger crops, had less pest and disease attacks, and most importantly to me, once established it needed less frequent watering.
This last was, and still is, vital to me as I've always loved to travel and it's immensely difficult to entrust a legion of diverse plants to the ministrations of a well meaning friend or two. To water plants assiduously is not quite an easy job, sure anyone can be conscientious but it is difficult to quickly learn the idiosyncrasies of the more unusual plants. Especially as on hot days some plants in pots need watering three or more times, and syringing too, if they are to thrive. Where everything is growing in beds or borders one good soaking will usually keep them happy for a week or more in summer, and much more in winter! Thus I advocated, and practised, a ruthless campaign of anti-plant-confinement gardening and begrudged having even house plants. (Needless to say the latter are cacti and succulents, even the aspidistra got planted out.)
Certainly apart from the convenience, which is reason in itself, I have observed plants growing in the ground are manifestly so much healthier in nearly every case and endure stressful situations so much better that there really seemed no argument for ever confining them in a container. Further I am convinced that for food to have maximum health giving value then the plant needs to have access to every nutrient it needs -but none of them in excess proportion. Thus a plant is likely to fare better and make better fare growing in a great mass of soil in the bed or border than if trapped in a small pot of compost, even with judicious liquid feeding and top dressing.
But over the years I have reluctantly come to realise that there are actually very good reasons for cropping some plants in pots and containers rather than in the ground. The biggest being 'a meal now, even a poor one, is better than the promise of the same next week'! Naturally I start off many tender plants under cover in small cells, moving them on into larger pots until they can be planted in the ground. I observed that when the tomatoes were inadvertently held too long in too small a pot size they produced a few tomatoes much earlier than the their more generously treated brethren. These happier plants looked better and gave bigger crops eventually but took longer doing so.
Like everything in gardening success depends on what you want. I want some tomatoes as soon as possible each year but without extravagant expense of heat or labour. For the surest and largest crop of tomatoes with no blossom end rot yet only an infrequent watering then putting the plants in the ground is best. But if like me you also want an early supply of tomatoes then it pays to keep at least some plants growing in pots. Exactly the same goes for new potatoes, I'm eating the first at Easter when I'm planting the last.
The reason is simple. By confining their root systems and restricting their growth most plants are brought into crop earlier than if allowed to run free in the ground. Much earlier. Moreover for early tomatoes or potatoes warmth is crucial for growth and a plant in a pot kept on the staging will always do much better than if planted into the cold ground of the border beside. In both a heated or an unheated greenhouse the staging will always be many degrees warmer than the floor unless air circulation fans are fitted. Even with fans and if extra heat is put underneath the plant's roots in the border with a soil warming cable there is still going to be more light up on the staging than lower down.
Because of the tremendous advantage of this greater warmth and light I have converted and gone over to growing more and more of my tender crops in pots. I have even made hanging open mesh shelves in the head space of my polytunnel to get some plants up into the warmest air feet above the staging. I originally used such a shelf to force some extra early strawberries (in pots of course). Seeing the difference it made I then grew my early cucumbers up there in big pots which cropped sooner than those in a hot bed underneath. This worked well till the weather warmed up and it became too hot up there for cucumbers when I replaced them with chilli pepper plants. The cucumbers became less demanding during the heat of summer grown lower down on hotbeds so for them pots are only worthwhile early in the year.
But pepper plants are even more noticeable in their response to pots than tomatoes or cucumbers. I've found that although you can get much bigger crops and chunkier bigger peppers when they are grown in the ground these come very very late compared to the early crops from pot grown plants. Indeed potted peppers standing next to plants growing in a raised bed (all under cover of course) cropped fruit before the bed ones were even well set. True the potted plants are stunted by comparison and yield much less in total but they crop many weeks sooner so they are worth the effort, especially as they can be kept in the warmest brightest space.
The same goes for aubergines, these again crop much sooner when in pots but the yields are much reduced and, like cucumbers and melons, these seem to suffer worse red spider mite attacks when growing in pots. All three crops need syringing or the early introduction of predators to keep them clean. Syringing is easier with plants in pots as they can be moved to a suitable spot and then inverted or rotated to ensure complete cover. So I guess the red spider problem balances out both ways, it's encouraged by pots but easier to deal with in them.
However pot culture is more demanding with watering, feeding and care. If melons are grown in pots then not only must they be carefully watered and fed but they must also be restricted to one fruit and the growth of sideshoots stopped by nipping out the tips. If this is not done too many unusable small fruits will result. Much the same goes for tomatoes which need more careful nipping out when in pots -but then on the positive side the plants do not tend to be as vigorous at making sideshoots as when growing in the border. Indeed that is much of the point of growing plants, especially perennial woody plants in containers.
For more than two decades I've grown dozens of different grape varieties, in a multitude of places and by a number of ways, and nothing has been as consistently successful as growing vines in big pots (ex paint containers about 5 gallon size). For more than a decade a half dozen different vines in pots have each given me an early crop, weeks ahead of those in the ground. Oh I've loathed the watering they demand but they have produced the goods! -and they are much more manageable. They suffer less from pests and diseases as almost everything is pruned off in autumn, what's left in the pot is then dumped outdoors and abandoned to winter's worst. When the pots are brought indoors during early spring they think it is summer and rush into growth which I train up, and then wind back down, a two metre cane stuck in the pot. (The border vines need continuous pruning all summer as they are more vigorous.) If five canes or so are allowed to develop on each vine I get about that number of bunches of grapes per pot. Not many but the plants do not take up much space each in their pots when trained vertically, and in the same ground space I could only squeeze in two varieties as they would be so much more vigorous in the border. And the half a dozen different sorts are preferable as they do not all ripen at the same time.
I find pot culture also works best for apricots, peaches and nectarines but not for cherries as even heavy crops are just too little in total. These plants are only put out in the summer and autumn, indeed their fruit is finished by July so they can be outside for five or six months of the year. As with grapevines growth is so much less vigorous that pruning is much reduced, indeed to almost none. I have tried the same fruits planted in borders and under cover the red spider mite problem is huge, as is scale, but in pots moving the pots outdoors for a while stops these pests being a problem. And when the plants are indoors they can sit in trays of water acting as moats stopping the pests walking or being carried on by ants. In fact these fruits are such thirsty devils they have to sit in washing up bowls of water during hot weather.
Indeed when you put plants in pots you then start to appreciate just how much water they need -though they will often survive on less by cropping poorly and growing miserably. Grapes, peaches and nectarines in pots are very very thirsty, as are guavas and cape gooseberries which are the worst waterholics, cucumbers, sweet potatoes and melons are nearly as demanding depending much on the weather. On the other hand peppers, aubergines, tomatoes and especially pineapples resent being wet, rather than moist, all the time, as do citrus.
And it would be foolish to put my citrus plants into a greenhouse bed or border as again they would get too vigorous and could no longer move outside for the summer. Sheer portability actually makes citrus feasible as in the ground outdoors they'd be lost in a hard winter and under permanent cover the pests would devour them. In pots they are also easier to give the soil conditions they need as their roots require more air than do most plants. I find they not only must have an open gritty free draining compost but I drill extra holes in the sides and bottoms of their plastic pots to ensure easier air and water drainage.
Pineapples too must have a gritty open compost and plentiful air to their roots and as they love heat they are ideal for pots which can be raised up as high as possible in the warmer air -not down in a pit as they used to be grown! Bananas on the other hand will just crop in a pot only as big as a dustbin, but do not give many fruits compared to those grown in the ground where they also gain on head space.
But still for the majority of vegetables and fruits I prefer planting in the ground, indoors or out. If I'm not after an earlier crop, or the plant is difficult, then the open ground is still best. Mind you for the reasons and plants above, containers come into their own. I just wish I could find an intelligent automatic watering system.