Snicker if You Will

I don’t know about your propagation space, but mine is getting overcrowded. Yes, now with a greenhouse, I’ve got more room than in the the past when I grew seedlings in windowsills or in my basement under lights. But my greenhouse is small, and with greenhouse beds home to fig trees and early spring lettuce, arugula, and other greenery, seedlings are relegated to a 12 by 2 foot shelf along the north wall.

I make the most of that shelf by “pricking out.” Snicker if you will at this Britishism, but pricking out is a way to get a lot of bang for your buck space-wise, whether in a greenhouse, on a windowsill, or beneath lights. It also makes more economical use of seeds.
Seedlings in spring, greenhouse
The process begins, for me, with either 4 by 6 inch or 6 by 8 inch seed flats, which are plastic pans a couple of inches deep with drainage hole drilled in their bottoms. I fill one of these with potting soil, firm it, and then treat it like a miniature farm field, making 4 or 5 furrows along the short length. I press these furrows into the potting soil with a board that fits the flat to the underside of which I attached dowels where I wanted the furrows.
Seed flats and furrowmaker
The first cool thing about this whole process is that each furrow can be sown to a different variety. I generally sow the flat to different varieties of the same kind of plant so that germination of the whole flat is fairly uniform. Looking over at one of my larger flats, I see newly emerged sprouts of Nepal, Belgian Giant, Paul Robeson, Amish Paste, and Blue Beech tomatoes. All taking up a mere 48 square inches!
Sowing lettuce seeds in flats
Flats of tomato seed were planted April 1st, watered, and kept warm, and those sprouts emerged today, the 6th. No light is needed until sprouts emerge. After a week , now with good light, those cotyledons (seed leaves) will darken and true leaves will appear. That’s when it’s time to actually “prick out.” Mind you, for two weeks, all those potential tomato plants have been getting started in a mere 48 square inches, the first week of which they didn’t even need light!
Lettuce seedlings
Other kinds of seeds take longer to germinate. Or shorter. And temperature also figures in. Tables of optimum germination temperatures for various kinds of seeds are available on the web and in some seed catalogs.

The Process

Pricking out is transferring the still tiny seedlings from the seed flat to individual cells to “grow on,” another Britishism. For these containers I’ve used saved cell-packs from plants I’ve bought in the past; now I mostly use Growease Seed Starters automatic watering  system from Depending on how many plants you’ll be growing and what you’ve got, small yogurt containers, even jumbo egg cartons could also fill the bill.
Pricking out containers
To start, I take a dibble, for this use, a pointed plastic cylinder about 3/4 inch across, and make a hole in one potting-mix-filled cell. (Etymologically, “dibble” originally was, or is, Manchester British slang for a police officer, from a character in a cartoon. How did that become the name for the black plastic thing I’m holding?)

Back to the seed flat . . .  time to lift individual seedlings out of their seed flat and into their newly dibbled hole. Those seedlings are very delicate and will die if the stem is injured. So I take a knife or a spatula and scoop up underneath a clump of seedlings to loosen the potting soil around their roots, and then take gentle hold of one of their leaves to lift the plantlet free.
Pricking out lettuce
After lowering one plant’s roots into its waiting hole, I firm the potting soil around the roots. No, not pressing against the stem, which could injure it, but pressing down into the potting soil. And not too hard. Just enough to firm it around the roots. One advantage of pricking out is that you can set the little seedling deep in the hole, up to its true leaves, so that the leaves are no longer supported by the weak, young stem.

Water is needed right away, either from below by sitting the container in a pan of water for awhile, or with a gentle shower from above. The newly planted seedlings are not turgid for a few hours so water from above often accumulates on the leaves to weigh down the plant. The wet leaves, flopped down on wet potting soil, are apt to rot, so with my finger I go plant by plant flicking off the water, and then the plants stand up straight.

After about 5 more weeks of growth with bright light and slightly cooler temperatures, the plants will be sturdy and the season will be ripe for tomato planting. Sometimes I caress my plants to encourage stocky growth, raking my hand gently over their tops, ideally once a day. The effect, called thigmotropism, is the same as that which causes dwarf, stocky growth of pine trees on wind mountain outcroppings.
Pricked out seedlings
Not all seedlings follow tomato’s schedule. Celery, for instance, might take 3 weeks to germinate and then another 9 weeks to grow to transplant size. (For details on when to sow, based on the average date of the last spring frost where you garden, see the vegetable section of my book Weedless Gardening.)

Followup on Previous Weeks’ Blogs

My first batch of birch syrup from a couple of weeks ago was, according to a friend who boiled it down for me, awful. “Worst thing I ever tasted,” says he.

But some of that syrup was cloudy from microbial activity during the warm weather. That could have caused that distinctive flavor.

Colder weather followed, and I tried again, discarding any cloudy sap. Boiled into a syrup, the flavor was still distinctive, not awful, but also not really good. Something reminiscent of cough syrup or molasses. The sap is high in fructose, which burns at a lower temperature than sucrose, the primary sugar in maple sap. It more easily takes on a scorched flavor, which my syrup definitely has, in excess.

Perhaps a species other than river birch would have been better, even good. The syrup is usually made from paper birch. All I grow here is river birch, though. They are, at least, beautiful trees.

And a followup on my overwintered artichoke plants. Or, I should write, my non-overwintered artichoke plants. Perhaps something will eventually emerge. No sign of anything yet, and I’m not hopeful.


It’s time to prune, and to help you, I’ll be holding a PRUNING WEBINAR on March 29, 7-8:30 EST. Learn the tools of the trade, how plants respond to pruning, details for pruning various plants, and enjoy a fun finale on an easy espalier. There’ll be time for questions also. Cost is $35 and you can register with Paypal or credit card here.

Choice Syrups

I’ve given up on maple syrup this year. The tree I tapped was too small to yield anything significant. 

I’d almost given up on river birch syrup. I thought perhaps it was the timing — and, have since learned, that it is! Sap from any one of a number of birch species doesn’t begin to flow until temperatures are consistently 50°F or higher, which arrives near the end of the maple tapping season and continues until about the time the trees leaf out.

River birch, tapped

River birch, tapped

Black walnut was another possibility for tapping. I previously had pooh-poohed it because, much as I love this tree’s nuts, I imagined the aroma of the leaves or the hulls oozing its way into the sap. Ugh!

Another reader reported that walnut syrup is delicious and I should try it, so I did. Sap started dripping as soon as I drilled the holes. The first batch is boiled down, and it is delicious. Not that different from maple syrup, with just a slightly different, smoother flavor. Nothing reminiscent of the nuts, leaves, or husks, though.

Black walnut tree, tapped

Black walnut tree, tapped

Processing was via the same low-tech approach I’ve used for maple syrup, merely adding each day’s “catch” to a big stock pot sitting on the wood stove. The woodstove is stoked pretty much continuously this time of year, so the sap is always evaporating, with the added bonus of humidifying the house.

I see a few eyebrows going up. Sticky walls and ceiling are what comes to some minds upon the mention of cooking down maple sap indoors. Well, that’s usually myth. Sticky walls and ceiling only result when the sap is in an active boil and bubbles bursting on the surface of the liquid send little droplets of sugar water into the air and onto walls and ceilings.

Until the final stage of my sap-making, the sap is just slowly evaporating. The vapor given off by slowly evaporating, simmering, or boiling a solution of any sugar and water is nothing more than water vapor. That’s why the maple (or black walnut) sugars become concentrated in the remaining liquid. They stay in the pot.

In those final stages of concentration, with much reduced liquid volume, the liquid can indeed reach an active boil. The pot of liquid announces that it’s nearing that stage by starting to gurgle like a baby, at which point it needs to be watched closely, mostly so that the syrup doesn’t get too concentrated or burn. The finish point is when the temperature of the liquid reaches about 219 degrees F. 
Boiling sap
I discovered a big difference from maple syruping when I attempted to strain off schmutz in the boiled down black walnut sap. The schmutz was a jelly that quickly clogged up the strainer. The amount of schmutz can vary from tree to tree, with time of year, and who knows what else. Turns out that black walnut sap is high in pectin, aka schmutz. Perhaps calling it “black walnut jelly” would make it more appetizing. Black walnut syrup

Too Late to Prune, Say the Squirrels?

Someone wrote me that squirrels were chewing on a Norway maple last week and the sap was seen dripping down, then went on to ask if that meant it was too late to prune. Perhaps the squirrels were enjoying some of the sweet sap.

Yes, you can tap and boil into syrup the sap of all kinds of maples; I’ve tapped and made syrup from silver maple, red maple, boxelder, and, of course, sugar maple. And each tastes slightly different from the other.

Getting back the pruning… It’s not at all too late. It’s fine to “dormant” prune any plants up until the time when they unfurl their leaves in spring. Actually, peach trees are best pruned when they are blooming.

Another good question might be: Why not just cut the Norway maple down to the ground? The trees are invasive and displacing our sugar maples, they have poor fall color, and they create lugubrious shade beneath which grass and much else can’t grow. Mostly, people keep these trees because they are already in place and full grown.