Nature is naturally transitional, easing into each new condition as time and the seasons pass, your vegetable garden should mimic this rhythm. I am seeing a lot of gardeners changing the species in their plots down at the community garden of which I am a member and a common pattern emerges. They usually rip-out the entire plant in order to create a 'clean slate' in which to install their new, warm-season varieties and this in no way mimics Nature nor is it healthy to an organic garden ecosystem...... that's the key word right there: 'ecosystem'. A vegetable garden is nothing more than creating habitat for insects using primarily food crops, think of it this way and it will become clear that 'clear-cutting' your garden every time the seasons change is not the way to go.
One lady had an absolutely gorgeous stand of bolting broccoli and Arugula in her plot, the plants were loaded with aphids and the associated myriad species of beneficial insects, numerous genera of pollinators swarmed the blossoms and tons of biomass in the form of roots which will enrich the soil after the plants are 'crowned'. 'Crowning' is a term (I think I just created) and it refers to the practice of cutting a plant off below it's point of above ground growth leaving the root system in-place. These roots will be consumed by the resident soil biology and soil structure will be enhanced as their 'shadow spaces' become conduits for movement of everything from the biology to water and air. Valuable stuff.
So, what to do. If I were her I would have selectively removed some plants to create a mosaic pattern and then installed SOME of my summer crops. As these mature and start to flower they create the habitat for pollinators and beneficials, they take-on the role of the fading species. As her winter crops continue to fade she can collect the seed and then crown them and install her remaining summer stuff; transition in this manner at every seasonal change. This way your garden is never without something blooming or mature structure for the native fauna. Install the new plants as close to the 'crowned' plants as possible and when the biology finishes consuming that old root system they will naturally migrate to the newly installed plants roots. Living plants attract soil biology to the rhizosphere, the root zone, the area of nutrient uptake with root exudates. These exudates are composed of carbs and proteins and are a major by-product of photosynthesis, soil biology chow. They eat it and poop and the plants 'eat' the poop. Poop is good stuff, soil biology poop is the best poop on Earth.
A clean and tidy garden, neat rows spaced evenly apart rarely provide the quality habitat that a natural, 'messy' garden does. Throw-in some herbs and even flowers to create diversity, after all, vegetable species are for the most part simply annuals that produce big, tasty fruit. This is just a mechanism for seed dispersal, a way to distribute genetics and increase range. Another good idea is to plant several varieties of the same species, this way you can see what produces best for your soil and climate types.
Be conservative and deliberate as you transition your garden and I think you will work less and produce more and I know your garden fauna will be much happier..........