Most Nutritious Winter Diet?

As most of you know, I live in Alaska. I am near no large towns or chain stores just to clarify further.

I have a leopard tort hatchling from Jodie and I am finding that the weeds are drying out and dying already as the weather cools off. All of the plantains are yellow, dandelion greens are getting dried out and all that leaves me with are clovers and grasses. I know spring mix is the go-to grocery store green but can/should anything else be included to further supplement his diet? I am looking into buying some seed mixes as well since the grass has really taken off in his enclosure to plant so he has more variety for foraging as well. Even though my guy is a hatchling, he readily snacks on the grasses I provide him. Mazuri and Marion Red block foods are being provided as well as calcium in both the form of cuttlebone and home made calcium carbonate blocks.

ETA - These are the seed mixes I plan on purchasing next week to add to his current personal crop;
Broadleaf Testudo Mix
African Grazer Grass Mix
Red Cowpeas

Wow, it's going to be 100° here next week I wish it was cooling down instead of getting hotter.
Anyway, it sounds like you're just going to have to set up a grow station in your house. Yourself you can to keep them growing all winter and just cut off some for your tortoise to eat. When he's Littles you could probably grow enough in his enclosure but as he gets bigger it will be easier just to have them growing outside of it.

My leopards really liked the African grazer mix . Some people say leopards aren't big into grass but all 3 of mine love it. Have you considered growing the mixes in pots or in window boxes? (Grow more save enclosure space)I had a good 4 trays of grass and the broadleaf mix going a few months ago.

It's still in the 65-70 degree range so window boxes aren't an option seeing as we have no AC and it's too hot to keep windows closed just yet. He's about 4 months old (still smaller than a bic lighter in length) so growing with him in his 6x3 foot enclosure is no trouble just yet. Does is sound like I have everything sorted out okay as far as supplementing his diet this winter?

You're going to have to get some grow lights.

Already have them! I'm growing grass in his enclosure now.

I built shelves and lights in a closet in my tortoise room. Grow what you can, use Mazuri and grassland tortoise food from zoo med, spring mix, escarole, endive, kale, carrot and radish tops, collard and mustard greens are all good choices from grocery. I also use herbal hay from tortoise supply. I mix it in with the grassland tortoise food.

I also have herbal hay so I can use that as well. I just wanted to make sure my game plan will be alright because it's happening sooner than I was expecting. We will be in a house at the beginning of the year so I can totally set up a 'grow station'.

A lot of grasses and weeds can be preserved for winter feeding too. You'll find this helpful as your tortoise eats more as he grows. For now, you could definitely begin freezing a lot of favorite leaves and grasses. Here's a few ideas: http://www.tortoiseforum.org/threads/these-can-be-frozen-thawed-and-retain-good-texture.128563/

Here's an example of a meal I made for my tortoise from completely preserved foods: Recipe and food (tort version)

Terribly sorry.
But what, pray tell, is winter ?