What's Coming Up 38: Divide Perennials, choose a kousa, beware treated lumber

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In this issue:

Choose a kousa dogwood but shed the shady notion
Make a cool move on woody plants
Divide to conquer huge Geranium and lavender
Look at the roots to divide and multiply
Some lumber's no treat in raised-bed veg gardens
Garlic mustard: Tiny seedling turns heavyweight weed
Break the rule, split the plant whenever you can:
            even in bloom, even bulbs!

Northern advantage: Stemless tulips a rarity
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Did you come here from a Search? You will find all of the topics below in this Ensemble edition. Download the pdf to read the articles.

Achillea, yarrow
            dividing WU38 Pg 5
Anemone x hybrida
, Japanese anemone
            dividing WU38 Pg 5
, columbine
            dividing WU38 Pg 5
, butterfly weed
            dividing WU38 Pg 5

            dividing WU38 Pg 5
baby's breath, See Gypsophila
balloon flower, See Platycodon
blanket flower, See Gaillardia
            dividing WU38 Pg 9
buttercup, swamp buttercup, See Ranunculus acris
butterfly weed, See Asclepias

           dividing WU38 Pg 9
Colchicum autumnale
WU38 Pg 9
columbine, See Aquilegia

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            Cornus florida flowering dogwood WU38 Pg 2
            Cornus kousa, Chinese/Korean dogwood WU38 Pg 1-2
crocus, fall, See Colchicum autumnale
            four-season plants WU38 Pg 1
, pinks
            dividing WU38 Pg 5
            frequency WU38 Pg 8-9
            guidelines WU38 Pg 7
            perennials WU38 Pg 3-7
            root type as guide for dividing WU38 Pg 5

            Euphorbia myrsinites myrtle euphorbia
                        transplanting WU38 Pg 9
            ostrich, See Matteucia
            suppressed by shade WU38 Pg 1

            propagation by layering WU38 Pg 5
, blanket flower
            dividing WU38 Pg 5
gardener's health
            life-extending work WU38 Pg 9
, cranesbill
            dividing WU38 Pg 3-4
gooseneck, See Lysimachia

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                        dividing WU38 Pg 5
            Ceratostigma plumbaginoides, plumbago
                       dividing WU38 Pg 5
Gypsophila paniculata
, baby's breath
            dividing WU38 Pg 5
, daylily
            dividing WU38 Pg 5
            mint WU38 Pg 5

            dividing WU38 Pg 5

           transplanting WU38 Pg 2

           transplanting WU38 Pg 2

            dividing WU38 Pg 5
, lavender
            dividing WU38 Pg 3-4, 5
, daisy
            dividing WU38 Pg 5
Limonium latifolium
, sea lavender
            dividing WU38 Pg 5
            rot resistant cedar, Juniperus WU38 Pg 7-8
           rot resistant cedar, Thuja WU38 Pg 7-8
            treated WU38 Pg 7-8
Lysimachia clethroides
, gooseneck
            dividing WU38 Pg 5
ostrich fern
            dividing WU38 Pg 5
, bee balm
            dividing WU38 Pg 5-6

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myrtle euphorbia, See Euphorbia

            dividing WU38 Pg 9
ninebark, See Physocarpus
Physocarpus ninebark
            transplanting  WU38 Pg 2
            dividing WU38 Pg 5
pasqueflower, See Pulsatilla vulgaris
            dividing WU38 Pg 3-7
                        frequency WU38 Pg 6, 8-9
            root type as guide for dividing WU38 Pg 5
, creeping phlox
            dividing WU38 Pg 5
, balloon flower
            dividing WU38 Pg 5
            treated lumber as source WU38 Pg 7-8
propagation WU38 Pg 7
            layeringWU38 Pg 3, 5
            offsets WU38 Pg 4, 5
            rhizomes WU38 Pg 5
            running roots WU38 Pg 5
            tap roots WU38 Pg 5

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Pulsatilla vulgaris
, windflower
            dividing WU38 Pg 5
            plants... behave like new furniture
            working like this for my life... WU38 Pg 9
raised bed
            wood used as retainer WU38 Pg 7-8
Ranunculus acris
, swamp buttercup
            dividing WU38 Pg 9
            indicate coming year's spread dividing WU38 Pg 6
            type of root as guide to dividing WU38 Pg 5

           transplanting WU38 Pg 2

            dividing WU38 Pg 5, 9
            affects flowering of shade tolerant species WU38 Pg 1
            importance of moderated temperature WU38 Pg 2
            Clethra alnifolia WU38 Pg 5
            layering to propagate WU38 Pg 3-4

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spurge, donkey tail, SeeEuphorbia myrsinites
sweetshrub, SeeClethra
            affect on tulip stems WU38 Pg 8-9
            moderated temperature in woods WU38 Pg 2
toadlily, See Tricyrtis
            timing WU38 Pg 2
, toadlily
            dividing WU38 Pg 5

            stems unusually short WU38 Pg 8-9
            cool season crops WU38 Pg 9
            raised bed WU38 Pg 7-8
            watering levee, watering ring WU38 Pg 2
            biennial weed eradication WU38 Pg 8
            garlic mustard WU38 Pg 8

windflower, See Pulsatilla vulgaris
wood, treated lumber WU38 Pg 7-8


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An image overview of this issue:


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Kousa dogwood gives us summer bloom, fall color and interesting form and bark in winter. Yet sometimes a tree doesn't flower well. In my experience, the most common reason for sparse bloom is too much shade. For instance, in 14 years the kousa in this photo never produced more than a few flowers. Then one winter the huge sugar maple behind it (trunk in the background) was pruned to remove a high overhanging limb. This gave the dogwood almost two hours additional light each day. 18 months later, after growing for a year in that improved light, the tree bloomed as you see it here, its first big show.




A watering levee is a ridge of extra soil an inch or two high forming a ring around a plant's root system. When Janet waters these transplants she pours into that ring. The levee holds the water to soak in over the roots.






This lavender branch (photo on left, below) set its elbow down on moist soil and grew roots -- we say it's a "layer" or that it "layered."

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A layer can develop on almost any woody-stemmed plant where a branch comes into contact with moist soil. Below, right: The lavender layer pictured here, related to the rest of its mother plant.
A gardener can encourage layering by lightly scraping the underside of a branch and then weighting it down to the ground or burying that limb while it is still attached to its parent. The limb continues to live off its mother plant's root system while producing restorative tissue called callus over its wound. Callus is capable of developing into any kind of plant part and usually forms root cells when in moist darkness. Cut the layer away from the rest of the lavender plant to grow it separately.

LavndrDivsn.jpg LvndrLayerS.jpg


Most geraniums have roots like the species known as bloody cranesbill (Geranium sanguineum, right and below). The plants more of themselves by both offsets and running roots. Notice the bumps on the roots -- each one capable of sprouting to produce a stem.


When you first start to look at roots the mass may be confusing even when a portion is rinsed of soil as in the previous picture. The drawing at left was made from that photo to highlight just the two parts of the crown indicated by the arrows. They are a mother plant (brown) which was able to produce enough starch to develop a fine root system of its own plus a daughter offset (red). The daughter has done well for itself, too, as indicated by its well developed roots

GeraniumDivsn.jpg GeraniumRootMassA.jpg

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Read the root to divide

Our procedure for dividing any perennial or shrub that we haven't divided before: Dig the plant, rinse the soil from the crown and at least one side of the root mass. That lets us see where to apply shears or knife to separate some rooted pieces.

There are just a handful of ways to divide. You don't have to memorize a hundred ways for a hundred perennials and bushes.

Offsets (below, left) are daughter plants that form at the base of a stem then develop their own roots and stems. Snap or cut between mother and daughter to make more of an offset. Hosta, daylily, astilbe, tall sedums, peony and daisy are some that multiply this way. The connection between generations is very strong and close in some plant species, less so in others. A daisy offset comes away with a tug, an astilbe offset must be cut away from a near-woody crown.

OffsetEchinacea.jpg TapRootAquil.jpg

Tap roots (above, right) are vertically oriented structures that become thicker at their top and may branch a bit at the bottom but keep one undivided head over the years. Each year that head has more eyes -- buds that can produce new stems. Balloon flower (Platycodon), butterfly weed (Asclepias tuberosa), windflower (Pulsatilla vulgaris), baby's breath, columbine and perennial statice (Limonium species) have tap roots. To divide a tap root, slice vertically through the root (below) to make a division that includes at least one eye.

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Younger is better division

As you cut to make divisions, keep in mind that the younger, outer portions of a perennial are the most vigorous in growth, bloom and health. Don't expect matching book-ends if you replant the old center and one of its divisions side by side. Daughter plants usually out-grow, out-bloom, stand straighter and show less pest damage than the mother plant.


 Above:  The foreground 'Violet Queen' bee balm is a one year old daughter division of the plan in the background/right. Given its own space to grow, the daughter became taller, longer blooming and kept its foliage more reliably than the crowded parent plant.

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Propagation references

Here are some of our favorite books for information about making more plants:PropgtnBks.jpg

Propagation: Fine Gardening How-to Series
            CD, Includes video of Janet Macunovich on Division; FineGardening.com

American Horticultural Society Plant Propagation
            Alan Toogood, Ed.; Dorling Kindersley, publisher

Park's Success With Seeds
            Ann Reilly; Park Seed (out of print - buy used)

The New Seed-Starters Handbook
            Nancy Bubel; Rodale Press Inc., publisher

Seed Germination Theory and Practice
            Norman C. Deno, 139 Lenor Dr., State College PA 16801

Plant Propagation: Principles and Practices
            Hartmann, Kester, Davies, Geneve; Simon & Schuster


In our own books we've combined the best from many sources plus our own experience. Use the index on our Asking About Asters CD to search by plant name and learn which of the six books on that CD have articles about dividing a given plant, then click to go right to the listed book and page.

Six of our books that are no longer in print are combined on the CD, Asking About Asters: Complete Library of Macunovich How-to.

It's 1,200+ printed, illustrated pages with one index. Order the Asters CD from our Market.


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No dividing while in bloom? We break that rule all the time!

Here's a barrow full of plants we dug to divide and transplant one late April day:WhlbrwDivNumbrd.jpg

1) swamp buttercup,
     (Ranunculus acris);

2) Sedum sieboldii;

3) daffodils;

4) myrtle euphorbia (Euphorbia
     myrsinites) - take care not to
     smear the irritating milky sap on
     your bare skin;

5) fall crocus (Colchicum

6) quamash (Camassia cusickii)

Still hesitant to divide when you need to, even when the plant's in bloom? Then come put your hands on at a Garden by Janet and Steven session to practice on our plants. There's a great opportunity coming up to do that. Come work with us in a gorgeous and celebrated garden May 2-4 in Berlin, Connecticut. It's a Garden by Janet and Steven and Cheryl!


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 45mph Garden: Blooming bulbs looked like no-stem tulips!TulipsDSC_6621.jpg

Tulips and daffodils may produce normal flowers that fail to reach the normal height. The blooms sit on stems only a few inches tall even though the plant formerly produced 18- or 24 inch stems.

This happens when the bulb did not experience enough cold -- the plant's chilling requirement wasn't met. It happens after unseasonably warm winters and when bulbs not planted in fall and stored warm are put into the ground in early spring. Plants affected in this way can be expected to return to their normal ways in future years.

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