What can you plant all year round?? BEETROOT!
....but it needs to be from seed in spring so it doesn't bolt (go to seed/flower) in the warmth. In any event I always recommend root vegetables are from seed as they don't transplant well.
As above seed is best. Beetroot seeds are quite big as seeds go so you can easily plant them individually. Dig a trench about 3cm deep or poke your for finger in the soil and space them about 10cm apart.
Beetroot are root crops which are not heavy feeders. If you are following a crop rotation cycle you do not need to worry about fertilising. If not then add some compost before planting or worm tea/bokashi juice.
It's important you don't plant beetroot where legumes have just been grown as the soil will have too much nitrogen. You will get nice leafy beetroot and small roots.
For baby beetroot harvest when they are 3 - 4cm wide or in any case before they reach 10cm wide. At this size they go woody and are not pleasant to eat. Beetroot will naturally rise out of the ground when they are ready to harvest but this isn't essential.
With beetroot, it's more about what they don't like that what they do. Keep away from tomatoes, dill, fennel and legumes.
Yes you can grow in containers but you won't be able to get many in round pots. Aim for square or rectangle pots which are at least 20cm deep and allow 10cm square for each beetroot. As always water crystals and self watering pots are essential so they don't dry out.
Beetroot is suitable for succession planting. This means that instead of having 30 beetroot all mature simultaneously, if you plant 10 beetroot at a time, every 4 weeks, you will have a continuous crop.