I am new to growing rhubarb. I live in Michigan and it is mid July. I found some clearance rhubarb roots and decided to give them a try. Can I plant them now, so they will come up next year? Also can I start them inside until they get bigger and then plant them?
Since you did get the roots, their best chance of survival will be planting them in the ground, and trying to get them as far along as possible by winter. Ideally, spring or fall planting is best. Rhubarb roots do not have extremely large energy reserves, so storing your root until fall may not work well.
Here are some good points to note when planting bareroot rhubarb in summer:
Do not let full sun reach the soil or newly emerged plants. Try to mimic spring conditions as far as possible, so try not to let it get hot. Use some kind of shade to protect the soil and the plant.
Keep the soil very moist. Do not let it dry out, even for a short time. This is critical to success.
Do not put manure or fertilizer in the planting hole. This can burn the roots. Finished compost is okay, and slow release fertilizer on top of the soil is okay. Rhubarb likes a very rich soil to start with, so fertilizing isn't usually needed during the first season.
If you plant them now, they will come up this year, and (hopefully) become partly established before winter. I wouldn't start them inside, mostly because that will mean either another transplant before the year's end, or trying to overwinter the rhubarb indoors.
Here are some of the conditions that will help your rhubarb plants succeed:
They like very deep and very rich soil, high in organic matter and nitrogen
They don't like drying out, and in the ideal rhubarb soil, this won't be a problem, especially if you mulch.
Established plants need as much sun as possible, even in summer in your area. The more photosynthesis occurs in the plant, the better it will grow.
An organic mulch helps conserve moisture, and keeps down weeds, while slowly building the soil. I use a shredded mix of lawn clippings and mushroom soil, because a plain straw or wood chip mulch will pull nitrogen from the soil while decomposing (although they release it again once decomposition is complete).
Michigan is a great area for rhubarb - the only thing I don't know is how soon your winter kicks in, because, as you suspected, it is a bit late to start new plants off. I suggest you pot them up in good size pots immediately, so that any root material isn't cramped, water well, stand them outside and then prepare an area where you want to grow them. This plant doesn't do too well contained in a pot over time, so you're aiming to plant a bit later, once you can see if they're growing or not. Rhubarb spreads quite a bit, so if you want more than one plant, you'll need to prepare a large area, so an average of, say, 4 x 4 feet per plant as an absolute minimum. Improve the ground by thoroughly digging, removing any roots, weeds, rubble and particularly pernicious weed roots, then digging in well rotted animal manure. Let that settle for at least a couple of weeks; in the meantime, keep your potted plants watered. If they start growing and look healthy enough, plant them in your newly prepared bed as summer comes to an end, or in fall. Water well and keep them watered up to late fall. Do not crop from the plants for the first year - they need that time to develop good sized crowns, and should be left alone to do so for that time.
Remove any dying leaves as winter approaches, apply an organic mulch for extra protection during winter, as they're young plants. Fertilise next spring, once growth begins.