Hi,

No, you shouldn't remove the foliage. We have had a fairly mild winter thus far so they are probably happy with the temperatures. You should just watch the weather and if we are going to have extreme dips in temperatures, you should protect them. We have had some cold nights so perhaps they are protected enough that the growth hasn't died back. 

Typically they do need to be covered when temperatures are expected to go below freezing. Cover it with frost cloth (Remay, for example), though you'd need to vent it for airflow and cooling on warm days. The cloth manufacturer should state on the package about how much temperature protection the product can provide, and you might be able to double-layer it to give a few extra degrees of protection. We suggest using hoop supports instead of laying the cloth directly atop the plants because any condensed moisture/dew on the cloth contacting the plants can encourage the formation of gray mold (Botrytis), which they are very vulnerable to contacting.

As for other long-term Ranunculus care:

• ideal planting season is autumn (as an example, cut flower growers sometimes plant Ranunculus at the same time they're removing tender plants light Dahlia which have finished for the season)
• corms can be pre-sprouted to check viability before planting but it's otherwise not necessary
  • when stimulating sprouting from dry-stored corms, rehydrate them by soaking in a tub of water for up to 4 hours; keeping the water oxygenated by using an aquarium bubbler or a slowly-dripping faucet can help avoid damage to the bulbs from oxygen depravation
  • plant sprouted corms right away after soaking and/or sprouting is observed
• plant corms about 1-2 inches deep and about a foot apart for good airflow; visible growth may take a month to appear
• to extend the bloom season (weather-depending, of course), plantings can be staggered about two weeks apart
• when plants go dormant by late spring or so (once foliage has turned yellow-brown), dig them up and store them in a warm, dry location, though you could experiment with leaving them as-is in the garden
• when fertilization is needed, calcium supplementation can help stems from splitting (though often calcium is quite abundant in our soils and doesn't need amending)

Let us know if you have further questions. 

Emily