Having missed the deadline for the Ideate stage, I'll include it here in order to complete the steps in order.

Ideate:
The refined problem statement I used is: "Market Gardeners have problems with misplaced tools and waste time going back and forth from tool storage to garden plot."
Ideas:
*Tool caddy (wheeled, carried, bag, box, sled, etc),
buy garlic (grocery store, farmer's market, CSA),
move shed closer (it already has wheels but it's too big to move easily),
put small sheds around garden (locker-sized with the exact tools needed for that plot),
*organize tool storage (wherever they happen to be stored),
*walkthrough the planting process ahead of time to find out what's needed,
*container gardening (pots, bags, barrels, buckets),
*lists of tools needed for each plot/plant/step/task (could be laminated and put in shed),
colour-code tools based on what task it's needed for,
discard tools that are in rough shape,
giant bungee cord to keep tools from getting too far from the storage area,
go super high-tech and use a robot garden (they do exist, and they would have all the tools needed),
switch to a greenhouse and keep the tools under the benches that hold the plants,
get someone else to grow the garlic for us on our property

I decided to have Thaila (my husband) pick his favourite idea(s). We're not looking to create a product to market, just a solution (or set of solutions) to make gardening easier for him. Many of the ideas weren't feasible, either due to cost (robot garden, greenhouse), practicality (giant bungee cords between the tools and the shed would make the tools difficult to use, container gardening isn't ideal for garlic) or simply because they don't fit our ideals and lifestyle (we're growing garlic to avoid buying it at the grocery store, Thaila wants to grow our food himself).
The ideas he likes are: tool caddy, organize tool storage, plan the planting process ahead of time, container gardening (not for garlic though) and lists of tools for each task/plant/plot/etc as part of the planning/organizing process.

Prototype: