Covering bare soil
Bare soil is not only prone to lose nutrients, it is also an open invitation to plants that we consider weeds to come and grow.
When we use phased planting, most areas of the Garden won’t immediately be planted with the plants we have in mind. To make sure these areas are still covered with plants, and thus not losing nutrients, or attracting weeds, they can be sown with a mix of plants that build up nutrients and cover the soil, while looking attractive.
Weeds are nature's way of both covering the soil and healing it. When soil is compacted, we will find weeds with deep taproots that break up the soil, like dock leaves and thistles. Poor soil attracts plants that build up nutrients, as they can cope well without readily available nutrients themselves.
When we cover our soil with plants, we can mimic this natural process, by planting plants that we like and that fulfil the same functions of breaking up the soil and feeding her.
When it is time to plant the area 'properly' the temporary 'weed replacing' plants will have improved the soil, and made it ready for the plants of our choice. We can leave some, if we like them, or we can slash them all back in the Autumn before planting, covering the plants and the soil with a mulch.