Please don't get caught up in the companion planting fad. It has little legitimacy and only creates problems. Instead focus on the differing needs of your various plants in terms of space to grow, water and nutrient needs.

It would be impossible to fit all you list in 1 6x4' planter. One tomato plant alone can take up 3 foot sq and pumpkins 2x that amount as they have 4-5' long vines. Onions and a pepper plant don't require much room depending on how many you are talking about. It is late to be planting bulbing onions but you can use them as green salad onions. Strawberries are usually grown as a perennial crop in their own location rather than mixed in with annuals. Is that possible?

As for "treating the soil" that depends on what you fill the bed with. Bone meal requires months to be of any benefit and provides only phosphorous so of benefit only if the soil is low in phosphorous. Some source of nutrients will be necessary - primarily nitrogen and potassium as well as the micro-nutrients and minerals - so mixing in a good all-purpose fertilizer could be of benefit and then supplemental feedings throughout the season.

As for the needs of the various crops - tomatoes need moderate amount of nitrogen, onions a great deal, peppers very little. Pumpkins require moderate amounts of N to begin with and then high does of P and K as the develop fruit. They all have different water needs as well - especially the onions and the peppers.

I'd suggest you begin by researching the various needs of each crop and then group what you can fit according to those needs. For example, do not plant the peppers near the onions.

It can be quite confusing and difficult trying to blend so many different crops into 1 small space so if an additional space is available it will make things much easier for you. Strawberries can work in a large container, so can a pepper plant, even a 5 gallon bucket with drain holes in the bottom.

Hope this is of some help.

Dave

Is this the planter outdoors? If so you are not going to be able to grow peppers outside in Scotland and tomatoes will be a struggle. I can't even grow peppers down here. It's just not warm enough. You might have trouble ripening pumpkins too. Strawberries are perennial so need a permanent site. Not a shared space. Leave the peppers and tomatoes in the greenhouse.

Forget about companion planting. It's largely nonsense.

To be sure of growing something successfully for the kids try peas, broad beans, lettuces, rocket, radishes, runner beans, courgettes, chard and other vegetables suitable for the British climate. 6 X 4 is big enough for maybe one or two courgettes and a runner bean teepee.

Floral and I were typing at the same time. ;-)

Agree about companion planting. Mostly mythology. But the root question here is what to do with your planter. Does the planter have a bottom, or is it just sides, as in a raised bed? If the former, it's a container and any serious attempt to grow vegetables in it will require a proper planting medium that is NOT just garden soil. A container with garden soil, no matter how well amended, will present serious problems in moisture distribution and retention. If a container, how deep is it? The depth will in many cases determine what you'll be able to grow well in it.

Start simple and grow potatoes, kale, pole beans/ bush beans, bell peppers. Those are all pretty tough plants. I'm not suggesting you try to grow all of those there at once. You could do kale, bell peppers and pole beans in your planter.

Bell peppers are not a good recommendation - they will simply not grow successfully outdoors in Scotland. Even down here in the South of England I can't grow peppers outside. Kale is a winter vegetable in the British Isles so can be sown in modules and planted out in June. But plants get huge and take up a lot of space. Runner beans do far better than French beans, whether bush or pole because we have cool summers and plenty of rain. In a small planter I wouldn't bother with potatoes which are plentiful, good quality and cheap in the shops. Whereas salad greens are far better quality homegrown and you can grow quite a lot in a small space.

If I had to choose one crop for a small space, ease of growing and interest for kids it would be runner beans. Courgettes are also easy and prolific.