Sowing time: mostly annual and biennial, but I’ll suggest you start in a bit cooler spans!
Soil medium: Ensure your growing medium is light loose and well drained. Do add a little boron and nitrogen for extra boost and fertilize well during the growing period with seaweed extract
How to sow and grow, sow them directly these aren’t a great fan of transplanting!
Pests: leaf miners, beet cyst nematodes, stem boring weevils, defoliating caterpillars are among a few that generally love your Chenopodiaceae family.
Disease fusarium and downey mildew is the most common of fungal infections you need to protect your amaranthus family from!
Companion flowers: try marigolds, sweet alyssum or nasturtiums.
Companion herbs: basil, mint can be grown around, although try to grow herbs in separate containers
Companion plants: brassicas or leeks would be a wise choice.
How to protect amaranths?
Try to use a net to cover your leafy greens, before putting in beet seeds, check the soil very well for fungus, if growing in containers sun soak the soil thoroughly, remove any twigs or dry leaves from under the soil.
Spraying cow urine will keep a lot of fungal and bacterial problems at bay.