The big roots that you see when you plant bareroot roses are used to anchor the plant to the ground. The feeder roots are smaller white roots that absorb the water and nutrients from the soil. The feeder roots are very sensitive and will fall off if the root ball falls apart when a rose is being transplanted. At least, that's my understanding.

Feeder roots are almost invisible tiny hairy like roots that grow from the anchor roots. All those roots you see on a bare root rose when you get it are anchor roots, even the smallest ones.
Feeder roots being to grow very soon as a rosebush is planted. These must grow before a rosebush can absorb moisture or nutrients. They are very sensitive to drying out and don't like sitting too long in water.
As athenainwi said, if the soil falls off the root ball when moving a rose it can go into shock until new feeder roots grow. That's why it's important to make sure you've picked the right place before you plant as moving a rose soon after planting takes it back to square one.

As the previous posters said, feeder roots are the small white roots coming off the anchor roots and enmeshed in the surrounding soil. To me this is another argument for buying potted plants rather than bare roots. You know the roots are alive and feeding in a potted rose. When a vendor ships a potted plant through the US mail, they're not just shipping dirt, but also feeder roots that increase survival. I like to transfer the shipped potted roses, or bands, into 3-gallon pulp pots with potting soil. Knock-on-wood, so far I have had 100% survival, even with the smallest bands.

Bare root roses have plenty of reserves stored to get them started while they develop a complete root system. If the bare root roses are planted quickly and nothing is done to inhibit its ability to produce feeder roots. (Read that chemical damage or sitting the plant too long in water.) 100% success should be expected.

Often we see people posting on this forum about scratching amendments into the soil at the plant's roots. Be aware that you may damage the feeder roots by doing this. These tiny roots grow very close to the top of the soil. It won't kill the plant hopefully, but it does not help it.

Well someone locally suggested that I scratch in some sand to help my aeration so how do I do that without damaging roots?

Beyond what has previously been written, if you want to promote feeder root growth, scratch and water in about 1/2 to 1 cup of potassium sprinkled around the drip line of your roses in the fall. Potassium is not a fertilizer as such, so will not promote new growth as the weather gets colder. However, over the winter it will promote the creation of feeder roots and they will really jump-start your roses come spring.

redsox, my advice would be not to scratch in sand, but maintain an organic mulch never less than 2" deep (it shrinks over the season). This will cause a crumb structure to develop in the topsoil.

Roses in a light organic potting medium will grow only feeder roots, and the fleshy roots don't develop. It's true that when you plant a potted rose, you are planting feeder roots. However, you may put the rose at a disadvantage regarding its ability to send fleshy roots out into the mineral soil. Potted roses start faster but bareroots do as well or better in the long term.

Karl said they don't like sitting too long in water. I am unsure about how long a bareroot should soak in water once you receive it. I have not done any bareroots yet.

Bareroots usually don't have feeder roots, maybe a few hairs just sprouting. Several hours is long enough soaking time unless you put a lot of junk in the water that discourages uptake. But bareroots can soak a couple of weeks if you aren't ready to plant.

Karl means that feeder roots will die in waterlogged soil lacking oxygen. If you are concerned about drainage, just do a drainage test.

I am almost totally ignorant of the technical descriptions of rose root anatomy, but, with reference to the linked picture of a bareroot rose from the Regan Nursery site, this is the way I think many rosarians refer to rose roots:

Three different types of rose roots are recognized

1) The heavier, pencil-like, roots are referred to as anchor roots.

2) The fibrous roots, readily visible to the eye, are called fibrous roots (what else?) or feeder roots.

3) In common with other plants, rose roots have innumerable tiny projections, properly called root hairs (NOT hair roots, which is a term often used for the type (2) fibrous or feeder roots). The root hairs are invisible to the naked eye and are key features for the uptake of water and nutrients. I think Karl, in the 3rd posting down, was referring to root hairs and not feeder roots.

Here is a link that might be useful: Anatomy of a rose

In my experience, soaking bare roots helps their survival. I've soaked them as long as 10 days and they did great in the ground.

I know this is an old thread, but I am hoping someone will see my question. I am transplanting a row of roses I was growing along my fence. They weren’t doing well and I thought they needed more water, better soil , something. I am transplanting them into pots so I can care for them better. 2 of them only have feeder roots, they were own root cuttings. The feeder roots are really dense and water doesn’t drain through them. The third that I dug up has feeder roots in the top 3 inches and some tap roots. Should I try to break up the surface so that water goes through?

I used a hose and cleaned them as much as I could. And then I potted them up in fluffy potting soil. I think I will water them every other day, or let the soil dry out in between, so hopefully they will grow down more.

I am in Oceanside CA 10A and moving to Portland OR in the spring. I was hoping to dig up my roses and bring them as bare root. But now I don’t know if they are basically feeder roots, if it will work. I have gotten lots of bare root roses and they never have the feeder roots around the top of the root system. I am thinking that they have been watered too frequently and not deep enough. Or maybe the rose growers really blast the roses with water and the break off? Do you think I will be able to move them to Portland?

I would notnot water them that much, put them in the shade for a while so they can recover from what you did to thenthem. And I would move them in pots, not bare rooted.

Will a moving van take roses in pots?

That's a good question to direct at your moving company of choice.