If your collards are bitter, not always, but usually it indicates they're not being picked while young enough. Same thing with mustard greens. When most do what is called "thinning" the plants, that's when they're ready.
For the record, there is a difference between "Family" greens, and "Company greens. Family greens, and peas are the ones picked while young, and tender. Company greens are the ones served to company, and they're picked when a bit further along.
The opposite is true for tomatoes. Only the ripest, sweetest tomatoes are served on the table, or in salads. The rest are used for sauces, and canning.
For the record, there is a difference between "Family" greens, and "Company greens. Family greens, and peas are the ones picked while young, and tender. Company greens are the ones served to company, and they're picked when a bit further along.
The opposite is true for tomatoes. Only the ripest, sweetest tomatoes are served on the table, or in salads. The rest are used for sauces, and canning.