I think if you Google nursery bed you'll find all kinds of information.

Probably quite a few of us gardeners have an area set aside from our main gardens for excess plants, trials, plants waiting to take the place of other plants, etc. I don't grow from seed, but I have old gardens with plants that need dividing and thinning out periodically. A separate nursery bed - which becomes yet another garden in itself - is a good place to spare them from the compost pile once out of friends and neighbors to give them to.

As for the actual construction of a nursery bed - I imagine many use the "lasagna" method of piling up layers of green and brown organic matter on top of a base of wet newspapers or cardboard. And some just clear out, prepare and amend a spot just as they might for any other type of planting venture.

A nursery bed, and a trial/test bed are not the same things. The purpose of a nursery bed is usually to grow plants on under fairly optimal conditions so they get big fast. I've known several people to take over parts of a vegetable garden for this purpose. There are also cold frames, greenhouses and other techniques to speed things up. A lot depends on the type of plants and the desired timeline.

The usual purpose of a test bed is to see how the plants perform under fairly normal conditions for that area. If normal means no watering, they shouldn't be watered. If normal means minimal amending, their soil should only be minimally amended. Part of the purpose is to weed out the divas.

Sarah,

I have what I call a 'holding bed'. I grow a lot of plants via the Winter Sowing method and in some cases want to check out some new-to-me plants before setting them out in the gardens and/or selling/giving them away. I will also check things out in terms of invasiveness and winter viability.

Up until last year I only had one such area, 5 feet by 12 feet, bordered by logs 9 inches thick and filled with soil and compost. Last year I decided to create two more holding beds and this year a few more will be created. I am looking to the future and do plan someday to simply garden in those areas - looking to the future as I age. :O)

Probably the most important thing to consider is accessibility. In my new HBs I made sure that I could reach in without walking on the soil so in the larger ones I created walking/stepping areas. Mine are raised, making access even better. There's always things planted to keep the soil healthy and active.

I think such garden beds are great to have. There's always room for plants to go in. Hope you try it. :O)