There are many plant companion settings. Plants that help one another out by promoting healthier growth, warding off certain pests, and helping keep the soil's pH at a healthy level for the plants around them. Let's look at Brassicas as companion plants:
For those that are not familiar with the Brassica plant family, these plants include broccoli, Brussels sprouts, cabbage, cauliflower, and kohlrabi. These plants repel wireworms which make them a great companion for potatoes, corn, wheat, and other cereal plants.
The plants that help the brassica family are alliums, borage, dill, geraniums, nasturtium, and rosemary. When planting your brassicas be sure to avoid planting them near anything from the nightshade family (tomatoes, peppers) or any mustards.
A tip on when and how to plant brassicas from Outreach Outdoors: Plant turnips, rape, and/or radishes 60-90 days before your first frost,
or mid to late July in the Midwest. Plant kale and swedes 150-200 days
before your first frost or in late April here in the Midwest. Be aware
that some kales will have a much shorter growing season, thus a much
later planting date. Conventional planters, no-till drills, or broadcasting seed can all
work. Seed should be planted at 1/8 – 1/4 inch deep. Till the soil, firm
the seed bed with a cultipacker or by driving an ATV over the plot,
broadcast (or drill seed) and repack.
If you are going to be broadcasting you may want to look into the Earthway line of Broadcast Spreaders.
When planting companion plants together, keep in mind that even plants
that help one another in other climates, soil conditions, etc. don't
always get along, as we post about companion plants, be sure to always
know that each garden will vary slightly from another and what works
for some may not work in your garden.