Why and How to Build

I’ve got to learn to look up more, you know, the way tourists do; natives generally fix their gazes straight ahead to a destination or downwards, in thought. I am reminded of this when a visitor (a “tourist” in this context) walks up my front path, smiles, and tells me, “I like your green roof.” So then I (the “native” in this context) look up and join in the appreciation.Two cats on my green roof

My green roof was born about twenty years ago. After fumbling too many times with packages or keys in the rain at the front door, the time had come build protection from the elements. Rather than cover just the area around the door, this cover would extend over a small patio. And rather than just shingle the roof, why not make it a planted roof, a “green roof?”

So my friend Bill and I built a sturdy, shallowly sloped roof supported on three corners by the walls of my house, and by an 8 x 8 white oak post in its fourth corner.Roof, ledger up The roof had enough slope so plants could be seen from the path, yet not so steep that a hard rain would wash the soil away.Roof completed

To keep the wooden structure dry, it was covered with EPDM roofing material and flashed with copper. A two-inch high lip of copper flashing along the low edge keeps plants and soil from sliding down off the roof. To prevent water from puddling at this lower end, I drilled holes and soldered short lengths of copper tubing at intervals into the lip, figuring that excess water would stream decoratively from each tube during rains. Roof drains(It streamed, but not so decoratively, because some tubes kept getting clogged and the bottom edge of the roof was not exactly horizontal so the flow burden was taken up by only a few tubes.)

How and What to Plant

Next was the gardening part of the roof. To keep the weight down, for low fertility to suppress weeds, and for good moisture retention I made a planting mix of equal parts peat moss and calcined montmorillonite clay (often sold as kitty litter).

The root environment on the roof was going to be harsh for plants. Only a two-inch depth of root run. And, in contrast to the moderated temperatures within soil out in open ground, roots on this shallow roof would experience mad swings in temperature that would closely mirror that of the air. And even though peat moss sucks up and holds moisture, there’s not much peat moss moisture to draw from in 2 inches of rooting.

The plant choice, given the conditions, became obvious: some kind of hardy, succulent plant. I chose hens-and-chicks. After filling enough 24 x 10 inch planting trays with the planting mix, I plugged in hens-and-chicks plants every 4 inches in each direction. Hens-and-chicks in traysAll this planting took place almost a year before the roof was readied for the plants, important so the hen-and-chicks could make enough “chicks” to spread and pretty much cover the planting trays, which otherwise would have left too much planting mix exposed to washing from rainfall.

Up the trays eventually went on sloping roof, laid down like tiles on a tile floor. Everything looked very neat and trim.Green roof, early on

Nature Collaborates

Despite very little intervention from me, the years have brought some changes to that green roof. This was not a garden area that I ever planned to weed, and I stuck to my plan. I figured that a green roof with a weed-free planting mix, sheltered on two sides by walls, and eight to ten feet off the ground would not harbor weeds.

I was wrong. Some weeds have moved in. Well, not weeds per se, because a “weed” is plant in the wrong place, and the roof is welcome to pretty much any plant.

Gazing up on my roof now, I see, in addition to the original hens-and-chicks, plenty of foxtail grass, quite decorative through the year with green shoots in spring and tawny, fuzzy foxtails in fall and winter. Also a single cedar tree about two feet high.Roof with weeds
More weeds on roof

I had a hand in introducing another sedum, Angelina. This sedum has borne small, yellow flowers and, just as decorative, its fleshy leaves turn a deep red color in winter. Angelina started out as a single plant I set in a nearby stone wall; over time a few plants of it appeared up on the roof. Angelina on roof

Angelina floweringShe looked good up there, especially when draped over the front lip. She also multiplied rapidly both on the wall and on the roof. To further encourage her, I grab bunches wherever in excess on the wall and toss them up on the roof to root.

One year I also planted oats left over from cover cropping in the vegetable garden. Oats’ extensive roots would be good to further knit together the rooting mix and lessen chances of rain washing it down. Planting involved nothing more than grabbing handfuls of oat seed, tossing them up on the roof, then waiting for rain.

Writing about my green roof has encouraged me to more frequently look up at it. It does bring a smile. Is that because there’s something anomalous about an aerial garden?

Brooklyn Grange

Urban farm high in the sky at Brooklyn Grange


Where’d the Red Go?

Sugar maples (Acer saccharum) are now doing just what I expected of them. But not exactly what I want them to do. Here in New York’s mid-Hudson Valley, at least, this autumn’s leaf show is not quite up to snuff. And it’s also later than in the past. It used to peak here in the middle of October; nowadays, with climate change, the peak has been pushed forward to about now.Autmn view of the 'Gunks mountains

Back to the color: This year the local sugar maples are mostly only yellow, lacking the oranges and the reds that, along with some yellow, really ramp up the blaze of landscapes and forests. Let’s blame that more subdued show on the weather. To know why, let’s backtrack to summer when, quoting from a section in my recent book The Ever Curious Gardener, Using a Little Natural Science for a Much Better Garden:

Green is from chlorophyll, most welcome in spring and through summer, but not what interests me in fall. Chlorophyll must be continually synthesized for a leaf to stay green. The shorter days and lowering sun of waning summer are what trigger leaves to stop producing it, unmasking other pigments lurking there.

Leaves’ yellow and orange colors are aways present, thanks to carotenoid pigments, which help chlorophyll do its job of harvesting sunlight to convert into plant energy. I offer thanks to carotenoids for the warm, yellow glow they give to gingko, aspen, hickory, and birch leaves.

Sugar maple

Sugar maple (not this year)

Tannins are another pigment, actually metabolic wastes, that, all summer, are hidden by chlorophyll. Their contribution to the fall palette are the season’s subdued browns, notable in some oaks and enriching the yellow of beeches.

Because leaves harbor carotenoids and tannins all summer long, nothing particular about autumn weather should either intensify or subdue their autumn show. The only glitch could be an early, hard freeze that occurs while leaves are still chock full of chlorophyll. In that case, cell workings come abruptly to a halt and all we’re left with is frozen, green leaves that eventually drop without any fanfare.

Autumn color also spills out reds and purples, most evident in red maples and some sugar maples, scarlet oak, sourwood, blueberry, and winged euonymous. Those reds and purples come from yet another pigment, anthocyanins. Except for trees like ‘Purple Fountain’ beech and ‘Royal Purple’ smokebush, whose leaves unfold dusky red right from the get go in spring, and remain so all season long, in most leaves anthocyanins do not begin to develop until autumn.Japanese maple

Anthocyanin formation requires sugars so anything that I or the weather does to promote sugar accumulation in autumn will increase anthocyanin levels in leaves. The weather’s role is to offer warm, sunny days to maximize photosynthesis, and cool, but not frigid, nights to minimize nighttime burning up of accumulated sugars. A cloudy, rainy autumn means less red because less anthocyanin is formed, and any that does form is diluted.

As I write this, it’s cloudy and rainy, as it has been so many days this autumn.

Other Reds

I was recently visiting my daughter in Pennsylvania. As we looked around her neighborhood I admired the rich, red, autumn color of the trees lining the streets. Red?! How can that be? What about what I wrote about this autumn’s weather and anthocyanin and red leaves in autumn?

Ah, but science takes care of that, too. Those trees in the Pennsylvania landscape weren’t sugar maples; they were a variety of Freeman maple (Acer × freemanii). Freeman maples are natural and deliberate hybrids of silver maples (Acer saccharinum) and red maples (Acer rubrum), the silver maple contributing fast growth to the hybrids and the red maples contributing strong branches and red leaf color in autumn. Freeman maple

Trees vary, both as to species and locations, in the amounts of pigments found at various times in their leaves. Red maples, as the name implies, have significant amounts of anthocyanins. In these trees, this anthocyanin is present not only in autumn as the chlorophyll fades, but throughout the growing season. Depending on the amount and kind of anthocyanin, its redness would be more or less masked by chlorophyll during the growing season. Some varieties of red maple, and many varieties of Japanese maple, are red or purplish all summer long.

The million dollar question is why a tree would have anthocyanin in its leaves all season long. Various theories have been floated. Anthocyanins do offer protection against excess sunlight, which is why young leaves emerge reddish on some plants.

Seedling red maples

Seedling red maples

(This characteristic does not correlate with the degree of red in leaves in autumn.) It’s also possible that anthocyanins could ward off pests.

Whatever the reason, red or orange or yellow leaves, I’m not complaining. Autumn is still a beautiful season here in the Hudson Valley. 



Pros for Hardwood Cuttings

Years ago, I had just one plant of Belaruskaja black currant. Now I have about a dozen plants of this delicious variety, and plenty of black currants for eating. Do you have a favorite tree, shrub, or vine that you would like more of. 

Hardwood cuttings are a simple way to multiply plants. This type of cutting is nothing more than a woody shoot that is cut from a plant and stuck into the soil some time after the shoot has dropped its leaves in the fall, but before it grows a new set of leaves in the spring. In the weeks that follow planting, if all goes well, some roots may develop and, come spring, this apparently lifeless piece of stem grows shoots and more roots, and is well on its way to bona fide plantdom.

(Be very careful, though. Multiplying plants can become an addiction. I speak from experience.)

Hardwood cuttings, kiwi, blueberry, grape

Easy to root

Success with hardwood cuttings depends on both your skills and the plant chosen. Not every woody plant is amenable to increase by hardwood cuttings. You can expect close to one hundred percent “take” with plants such as grape, currant, gooseberry, privet, spiraea, mulberry, honeysuckle, and willow. But this method generally is unsuccessful in making new apple, pear, maple, or oak trees. 

Because they lack leaves, hardwood cuttings are less perishable than “softwood cuttings,” the leafy stem cuttings that are taken while plants are in active growth.Blackcurrant and plum cuttings

If you’re a novice and want to make your thumbs feel greener early on, try your hand with hardwood cuttings of willow, a plant I have seen take root from branches inadvertently left on top of the ground through the winter. Most other plants demand a little more finesse to ensure success with hardwood cuttings.

Gathering Wood

All right, so you have a woody plant you want to multiply by hardwood cuttings. Step back and look at the plant before you take wood for cuttings. Look for some young shoots, those  that grew this past season; snip them off for cuttings. The shoots most likely to root are those of moderate vigor, not too fat and not too thin for the particular species.

Black currant, 1 and 2-year old stems

Black currant, 1 and 2-year old stems

Plum, 2 and 1-year old wood

Plum, 2 and 1-year old wood

Once you have one or more shoots “of moderate vigor” in hand, cut them down to a manageable length of eight inches or so. Look for the nodes on each branch; these are the points where leaves were attached. Make the cut for the top of each cutting just above a node, and the cut for the bottom of each cutting just below a different node. 

Make sure the upper end of the cutting, which is the point that was furthest from the root, is planted pointing upwards. The plant “remembers” this orientation and responds accordingly, growing roots from the bottom and shoots from the top of each cutting. (Although it’s not impossible to root upside down cuttings, there’s just less chance of success.) Professional propagators cut the bottoms off squarely and the tops at an angle so that the ends don’t get mixed up during planting.

Success Comes With . . . 

Plant the cuttings in your garden where the soil is not sodden. Without good drainage the cuttings will rot, rather than root.  Make a slit with your shovel, slide in a cutting until only the top bud is exposed, then firm the soil. The rooted plants should be ready for transplanting to their permanent homes by next fall.

Cuttings can be set in the ground for rooting either immediately or stored through the winter for setting out in early spring. I’ve had better success with fall, rather than spring, planting. In the spring, the cuttings often are overanxious to begin growth and the top growth is well underway before the roots have begun. The shoots soon realize that there are no roots to sustain them, then flop over and die. 

With cuttings planted in the fall, roots have the opportunity to develop from now until the soil freezes. In the fall, soil temperatures drop more slowly than air temperatures so there’s still some time, depending on your location, before the soil freezes solid. New shoots, on the other hand, won’t grow until next spring, after they feel they have been exposed to a winter’s worth of cold. (This is a natural protection mechanism that prevents plants from resuming growth during a warm spell in January.) Come spring, the shoots that grow from the tops of the cuttings will already have at least the beginnings of roots to bring sustenance.

Blackcurrant cuttings in spring

Blackcurrant cuttings in spring

Mulch fall-planted cutting so that alternate freezing and thawing of the soil doesn’t heave them out of the ground.

Cuttings could even be planted in pots with a well-drained potting soil, as long as the pots are kept cool (30-45°F) long enough for the shoots to “feel” winter, so they can grow shoots in spring.

If you’d rather plant in the spring, the cuttings need to be kept cool and moist through the winter. The traditional method of storage is to bundle the cuttings together and bury them upside down in a well drained soil. Why upside down? Because the bottoms of the cuttings then will be first to feel the warming effects of spring sunlight beating upon the ground, while the shoot buds are held in check buried deeper in cold ground.

A refrigerator can substitute for the traditional burying. Seal the cuttings in a plastic bag, wrap the bag in a wet paper towel, and then seal the whole thing in yet another plastic bag. Plant as early in spring as soil conditions permit.

Pay attention to what works and what doesn’t, figure out why, and you’re on your way to propagation addiction. Next worry is what to do with all your plants.