Crocus blooms so early and the foliage dies back pretty quickly so it would be ok to naturalize it in your lawn. The foliage often dies back before you have to mow the lawn the first time in spring.

I agree with Blueheron. Furthermore, the foliage is so thin that you can hardly discern it from grass blades. If you really want to mow the lawn before all the leaves dry out, just set the blade the highest. The crocus will have enough foliage to make nutrients for the following year.

Have to respectfully disagree with Blueheron.
First, there are early (species) and there are late (vernus) crocuses, that as a rule bloom two weeks later. Even within vernus group could be a 2 week difference between bloom time.
Also, such factors as sun exposure and depth of planting will affect bloom time even for the came cultivar.
If you plant late ones in a grass and area will not receive really full sun you might be facing the same problem I had this year, crocus vernus 'Rememberance' bloomed toward the middle of April and foliage was present till mid-late May.
However, if you opt for species (which are better naturalizers anyway) and plant them in a most sunnier part of your lawn you'll have the most spectacular show you could possibly get in early spring.

I have several hundred around my back lawn on a slope leading into the edge of the woods along with snowdrops, Iris reticulata and spanish bluebells. I find that mowing very late in the fall gives a long enough lag time in the spring that I can let the grass grow a bit longer and leave the bulb foliage to mature.

Besides, a lawn is only good for keeping the mud and weeds down between the flower beds anyway. JMHO

George

I have one lawn that is full of crocus, some early, some late. The leaves certainly don't die down before the grass needs mowing. That isn't a problem for me and I leave it as long as practical, then mow. My reel mower actually misses a lot of the crocus leaves which are up to a foot long by that time. Even if they are cut early the crocus still come back, maybe just don't spread quite as fast. Sometimes I'll take the opportunity to spike the lawn and topdress, which means another couple of weeks before it needs to be mowed.

Thanks for the info. When I buy Crocus bulbs, will it specify on the package whether they are species or vernus?

rudy, Costco's, BJ's and HD's packages usually say either 'large flowering crocus' or 'crocus vernus'. Those are later blooming.
Those that marked as c.tomassinianus, c.sieberi or c.chrysanthus (probably the earlist of all) are species.

Your crocus package label will probably tell you absolutely nothing useful about them, except the colour :)

Sometimes the label will refer to them as species crocus, snow crocus, or some such term. They may also be described as good for naturalising. These are usually the small flowered forms and tend to be earlier. I find the yellow ones flower first, probably closely related to C. chrysanthus, followed by the other colours.

When a label refers to dutch hybrids or large flowers they will generally flower quite late. Labels referring to vernus crocus or crocus vernus are not likely to actually be the species Crocus vernus but will be late-flowering hybrids based on that species.

C. tommasianus is perhaps the easiest to identify since it is often labelled by name, or by the few cultivars: Ruby Giant; Whitewell Purple; Roseum. They flower quite late for me, but are described as flowering early by almost everybody else ;)

What about the impact of weed and feed on the lawn? We do have a lawn service do that each year.

Nikhil