Yesterday when my son and I arrived home after preschool, I could see my shadow against the driveway's thin layer of snow. Night falls early at this season, and the sun had long since set. The shadow came from the half-moon suspended over our rooftop.

"Look, mommy -- stars!"  We stood there for a moment, our breath drifting up like fog, marveling at the sky. And then I hustled us indoors, because although we're not in the deep freeze of the midwest, the mercury was hovering around zero.

Having a child who likes to look up at the sky helps to keep me attuned to the ebb and flow of the seasons, the waxing and waning of the moon. Of course, so does the Jewish calendar. I wasn't surprised that the moon was half-full already; I know that next week is Tu BiShvat, which always falls at full moon.

The New Year of the Trees. The birthday of the trees. The day when we count trees as a year older than they used to be, even though we no longer tithe their fruits. The day when we believe the sap starts to rise to feed the fertile season to come. Even here, where the ground is rock-solid, impregnated with ice.

If we get days which are warmer than freezing and nights which dip back down into 20s, maple sap really will start rising soon. I always look forward to the year's first maple breakfast at our local sugar shack -- a sign of impending spring even though soft rains and crocuses remain months away. But Tu BiShvat is about more than literal sap creeping up the phloem.

Tu BiShvat is when our spiritual sap starts rising to prepare us for the coming spring. We've been reading the story of the Exodus from Egypt in our cycle of weekly Torah portions; at Tu BiShvat, we take our first step toward Pesach, our celebration of freedom which marks spring's new beginnings. At Tu BiShvat, we assert our trust that our dry and cracked winter souls will be watered and nourished. We open ourselves to feel the abundance which is flowing into our hearts and spirits.

We are the trees, growing older year by year. We give ourselves over to trusting that in the fullness of time, our labors will bear fruit. That we will bring forth nourishment for ourselves and those around us. That this world of winter will end, and be replaced by spring's warm breezes -- and summer's clear sunshine -- and autumn's blaze of red and gold -- again and again, and again.

I make my way to the storage room adjacent to our garage where curls of etrog peel have been steeping in vodka since Sukkot. I decant the liquid, add a simple syrup of sugar-water, and bottle it: etrogcello, made from the pri etz hadar, the "fruits of the goodly tree" (a.k.a. etrogim) which were so central to our celebration of Sukkot. Pri Etz Hadar is also the name of the first haggadah for the Tu BiShvat seder, published in 1728.

When we sip this sweet bright fire at our Tu BiShvat seder next week, we'll swallow a taste of the autumn behind us -- and an anticipation of the autumn which is to come. Sunshine in a jar to nourish our souls, all the way down to the root.