Where are the flagstones located. In the full sun. In full shade. In dappled shade.
What kind of soil is under the moss?
How new are the flagstones (are these rocks or the cement ones)?
What kind of moss? Where did you get it from?

There is an alternative to moss for flagstones:
It is called Irish moss and is a moss like ground cover that you can find at Home Depot. It should do great in full sun and in shade and is not too fussy about any lime leeching out of the flagstone (if the concrete ones).
and it can take dryness.

For real moss sprinkle every day!

You could try Leptinella gruveri aswell, it looks like a tiny fern/moss grows to 1 inch and is hardy to 7, if thats not hardy enough there are slightly larger species that are good to 5, And as always, wolly thyme makes a good choice.

Here is a link that might be useful: Miniature Brass buttons

socalflower,

Sorry to hear your moss is not growing.

1. Where did you get your moss? Was it growing in a similar type of setting to your flagstones?

2. What is under your moss in the cracks? Is this similar to the type of soil from which you took your moss?

Crack mosses are usually the Bryums which like sand and weathered concrete. Since your moss is alive but not growing you are correct it needs something. I am assuming you live in a usda zone like 5+ and get reasonable spring moisture.

Make sure the moss is packed down tightly onto soil/sand in between your pavers. Give the moss water, mist or spray. IF you have been watering then it might be that your water is not compatible with the moss. I use rainwater or distilled.

Many people assume since the moss doesn't die when they water that their water is compatible. If your moss doesn't grow when you water from your tapwater then most likely it is your tapwater that is at fault. A small hand pump (one gallon size) and a gallon of distilled will water a ton of moss.

Fertilize 1/4 strength acid fert like for azaleas or rhododendrons every three weeks.

Rick

Terrestrial Man - I see you are in zone 9. I have Irish moss and wondered about planting beween flagstones which are partly in sun and partly in shade. My research says it grows only zones 4-7. Are we talking about Sagina subulata or something else? So far mine is planted in a shady damp place and looks fine. I am waiting to see what happens in our wet, hot summer.

Sagina yes!
I think you should be ok. it depends on the kind of soil.
if it drains off good then i would think the plant will succeed. i think sagina likes water but likes good soil aeration too. you may want to google on different cultural approaches. out here it can be planted in full sun and I am sure that it gets its share of abuse and dryness.
there are two varieties: a light yellowish one and the darker green one.
don't know if one is hardier than the other.

how much shade is enough shade for moss ???? 2, 4, 6 ???

DiDi,
Wow forgot about this thread!
Shading on moss varies per species. some do best with much
while many can handle some sun, such as Brynum species. My feelings are that most moss will handle the thin light of early morning and late late afternoon. I think that some sun is important and that dappled light is suitable for most species. If you are using native species than be sure to keep notes on the environment that you found them in and if possible revisit the site of collection at different times and seasons so you can learn more. Most of my info on mosses come from experimentation with non native species. Would you believe that I have yet to master the artificial cultivation of a native Brynum that grows quite well in the gutter along the roof of my van in partial shade whereas a Brynum species from Utah is very versatile and can handle direct sun (No. Santa Barbara County, California) with only a thin soil base. So the best approach is to experiment! Even attempting to grow under dissimilar conditions to their natural sites. Take images and keep notes!

gardeniadyl
have never beem able to get sagina to go through summer .
When the heat and rains come it goes down hill.
Beautiful during winter though.
I use tropical selaginellas .Martensii but only in shade.
Nothing seems to handle the summer sun lol gary

When I want most mosses to spread I add a little moss to some soy milk in a blender and make myself some moss paint. Now I only work with native moss in zone 5 but I can paint it on a rock with very little dirt and get good results.I used to lay out trays with a quarter inch of soil and put the moss milk all over it and keep it damp but not wet ... then use it like moss sod.

When is the best season to plant Irish moss? Is it possible to plant it between flagstone in the heat of July? Also, what would be a nice compliment to the Irish moss and Flagstone along the sides of the patio? Thanks,

Possibly an Echeveria species or hybrid. These enjoy partial shade and can handle less water as can the Irish moss. I would think that the Irish moss should be planted early in Spring for the best results.

I have natural moss forming inbetween my flagstones. Is this desirable moss? I was going to plant Irish moss this October. I didn't know if this was considered a weed and I should pull it out. It is doing a nice job holding all the sandstone in its place. Please help!

keep the moss. kiss off the irish moss

I like making a moss shake of a bottle of beer, 1/2 tsp of sugar and couple clumps of moss (can usually find something in the yard), blend, paint on, and mist daily. and I agree w. terrestrial man, keep the moss.

Finally a more productive use of beer! Wonder if it makes
good fertilizer????

I too am interested in growing moss between some natural limestone stepping stones in a walkway I recently installed. I am seeking a type of moss that will thrive in the climate of central Ohio and in areas that are full sun and dapple sun. The soil appears to be decently rich, but I have added a bit of sand to in when I installed the walk... If needed, I can add a layer of "unsanded" soil. I am also seeking some additional input on the soy / beer "moss shake" method. Thanks for your help. JBR

Here is a link to a very excellent website about mosses.
It is the website of the Ohio Moss and Lichen Association.
Since you live in the state you may want to join the group and attend one of their forays.
The moss below looks promising for your situation, besides the usual Bryum.

Here is a link that might be useful: Ceratodon