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Archive for September, 2012

Dividing a Tree Peony

The principle method by which tree peonies are propagated is by grafting. This is a rather involved, labor intense procedure. Much simpler is to propagate your favorite tree peony by means of division. The technique used for this is similar to that for dividing herbaceous peonies.

Not all tree peonies are good candidates for division. Only those which are growing on their own roots will successfully divide. Tree peonies with only one or two main trunks should NOT be divided. Most likely a tree peony with this kind of growth habit is not growing on it’s own roots and is still reliant on a large grafted herbaceous peony nurse root.

Also, before deciding to attempt to divide a older, well established plant, remember that tree peonies are slow growing. It will take many years before divisions attain the grandeur of a mother plant a peak bloom. With that said, lets get chopping!

First, choosing the right plant to divide.

With only two main trunks, this tree peony would not make a good candidate for division. In this case it is even possible that the plant is not on its own roots and is still reliant on its grafted herbaceous understock. Attempting to divide a plant with this form my result in no viable divisions.

A multi-stemmed tree peony is a good candidate for dividing.

Notice many vigorous stems from the base. This is indicative of a spreading root structure.

Before digging up a peony, remove the leaves. Begin by digging around the drip line of the plant.

After loosening the soil a bit, remove some by hand from around the base. This will help to free the roots from the ground.

Dig around the plant some more. Be patient, good divisions are dependent on undamaged roots. Roots are easily broken by hasty and careless digging.

With enough soil removed, the plant should just ease out of the ground with a little gentle prying.

Quite a crater is left from the excavation!

The next step is to wash off the roots.

Since most tree peonies are grafted, its probable that even a very well established plant will still retain the original herbaceous graft root in addition to its own roots. In this photo both are clearly visible. The herbaceous graft root is dark and bulbous, while the tree peony roots are lighter in color as well as much longer.

We like to allow the plant to ‘rest’ for a few hours. We wet the roots and cover them with damp burlap. This allows the roots to dry ever so slightly and results in them being less brittle and thus less prone to break during the division process.

The two main tools you will need are a sturdy pair of garden snips and an large old kitchen knife. Be sure to wipe your tools down with isopropyl alcohol before beginning. This sterilization will prevent harmful bacteria and fungi from spreading via the cuts you will make.

If the herbaceous nurse root is still present, remove it before beginning the actual divisions.

The herbaceous peony nurse roots should slice off relatively easily.

Once removed, the old herbaceous peony nurse root can be discarded. Or you might try replanting it. Its possible that small, heretofore dormant buds will begin to grow on it. If you do this, expect to wait a few years before you see a flower from your new herbaceous peony.

Now you are ready start dividing. The first step is see where the plant looks like it might naturally divide. This allows you to visualize the cuts you will need to make. In order to be viable, a division must have both buds for above ground growth as well as adequate roots.

Look for naturally occurring divisions that seem to have both adequate stems and roots. Take special note of the new tree peony shoots coming up from the crown of the plant. Be careful not to damage these.

Its often best to initially try prying the plant in half. You may need to call a helper at this point.

A well placed snip will break through a shared piece of root.

The roots are very intertwined, so be careful and pull divisions apart gently.

One of the resulting divisions. It has a good stem to root ratio.

You may want to stop at simply splitting the plant in half, or you might opt to maximally divide your plant.

We have chosen to maximize the division of this rockii tree peony.

Further division beyond a simple split will probably require cutting through the hard, woody crown of the plant. Keep your helper around to help with this as well.

When you are satisfied with your divisions, clean them up. Trim ragged cuts and removed blackened bits of root.

To ensure that the above ground buds will not put too great a strain on the roots, we recommend trimming the top growth back by as much as 1/3.

In the case of very small divisions with little root, totally remove the woody top growth in favor of new, more vigorous buds.

The end result:

Three large plants, one medium, two small, one x-small and lots of scions to graft. Replant new divisions immediately. If the roots dry out, the plant will take longer to establish in its new location.

Dividing an older tree peony is not for the beginning gardener, nor the faint of heart. It is a given that the new divisions will take a few years of growth before the begin to flower well. In the end however, the result will be many more tree peonies to enjoy. Should you have any questions regarding this post, please do not hesitate to contact us.

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A few months ago we wrote about how to identify the herbaceous peony understock sprouting on a grafted tree peony.  This is usually the result of the grafted tree peony being planted too shallowly.  Now that the season for transplanting peonies has arrived, it’s time to dig up and remove unwanted herbaceous understock as well as replant the tree peony. It is necessary to do this because if left unchecked, the herbaceous peony can eventually overpower and choke out the tree peony. If you do like the way the herbaceous understock blooms, you can replant this and let it grow out.

If you have a tree-herbaceous chimera peony, now is the time to dig it up, remove the unwanted herbaceous peony suckers and replant the tree peony deeply enough so that it will grow its own roots on which it will thrive for many years to come.

Tree peony leaves are easily distinguished from those of herbaceous peonies. Tree peonies are dissected and three pronged, while herbaceous peony leaves are elliptical and pointed.

If you are unsure about the difference of the leaves, you can always check the stems. tree peonies are woody, while herbaceous are green.

Remove the leaves before digging up and peony. Dispose of these in a hot compost pile or outside of the garden least they spread harmful fungus throughout the garden.

The best method for digging up a large peony is to do it carefully. Being by digging around the circumference of the plant, about 18” away from the drip line. Then remove some of the soil from around the roots, lastly gently ease the plant out of the ground.

This plant had a smaller root system the anticipated.

The majority of this plants roots are herbaceous peony roots, it has very few tree peony roots. The herbaceous peony’s ‘eyes’ are the small white buds which have formed at the bottom of this year’s herbaceous stems.

Because this plant has so few tree peony roots, to remove all the herbaceous roots now would kill or weaken the tree peony. Best now to remove the herbaceous peony ‘eyes’ by trimming these pink or white buds. Replant the tree peony deeply so that it can grow its own roots over the next few years. Plant the tree peony about 4” above the graft union, or where the herbaceous peony roots begin. Take this opportunity to properly amend the soil for the tree peony. Place a shovel full or two of compost in the planting hole. As you back fill, mix in a cup of limestone dust if your soil is acidic. Mix in a few more shovel fulls of compost as you fill in the hole, mixing in a cup of Azomite to give the plant a mineral boost.

As you back fill, water in the soil/compost mix so that it settles well around the roots. Tamp down the soil and top dress with a shovel full of compost if you still have some handy. Newly planted, or replanted peonies should be mulched for their first winter in the ground to help prevent the soil around the roots freezing and thawing suddenly and heaving the roots above ground.

Tree peonies can be transplanted anytime now from now until early November in our USDA zone 6. The most important thing is to make sure that the roots do not dry out while out of the ground. Remember to plant in a sunny, well drained location, with rich soil and a pH of at least 6.5.

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Some of our favorite tree peonies we grow here at Cricket Hill Garden are hybrids of the wild species Paeonia rockii, also know as Gansu Mudan. This species of tree peony grows predominantly in Northwest China. The area around Lanzhou city in Gansu province is particularly known as a center for the breeding and propagation of P. rockii. We imported our first rockii tree peonies about fifteen years ago and were immediately enchanted. With their finely cut foliage and erect habit (mature specimens reach to well over 6′), P. rockii hybrids make for quite a regal planting. The blossoms are nothing short of spectacular, large and fragrant they are found in a range of colors, all sporting dark magenta flares at the base of each petal.

Snow Lotus is closely related to the wild species P. rockii.

Cup of Shining Night is one of our favorite P. rockii hybrids developed by Chen Dezhong of the Peony Peace Garden in China’s Gansu Province.

Over the years, we have noticed that our tree peonies with P. rockii heritage are much more likely to go into early dormancy during the late summer. With much of the county experiencing very hot and dry weather this summer, we have heard from many customers who have noticed that their P. rockii tree peonies leaves have turned brown and shriveled. This of course happens to all tree peonies as they drop their leaves and go into dormancy. Typically this occurs in early October here in Connecticut, however it seems to happen much earlier to P. rockii tree peonies during drier years. We have also noticed that P. rockii planted in the full sun loose their leaves much earlier than those planted in conditions of dappled or partial sunlight.

This P. rockii hybrid receives full morning sun but is shaded in the afternoon. It still retains most of its foliage, though some has begun to turn brown.

This P. rockii receives almost no direct sun and still has very green leaves. One of the great advantages of P. rockii is that they will grow and bloom well in more shade than other types of tree peonies. A shaded planting location like this more closely mimics the natural location in which P. rockii grows in the wild.

The effect of the strong summer sun on the foliage is clearly shown in this picture. Notice the brown and yellow leaves on the right side of the tree peony. This side receives full morning sun. The deep green foliage on the shrubs left side faces west but is shaded by tall trees and receives no direct afternoon sun.

The most extreme case. This P. rockii has had its leaves totally fried by the hot summer sun. It is planted in a full sun location in our garden.

Once the old leaves are removed, its clear that this plant has set good buds for next year. We do not find that early onset dormancy has any significant effect on overall plant performance. If your rockii tree peony has already gone into dormancy, remove the leaves and dispose of them in a hot, regularly turned compost pile or outside of the garden.

Planted only a few feet from the rockii shown in the previous picture is another Chinese tree peony which still retains most of its foliage. This particular plant is ‘Flying Swallow in a Red Dress’ and is a member of the Central Plains cultivar group. This type of tree peony is much farther removed by centuries of cultivation and selection from any of the wild species tree peonies than P. rockii hybrids. In our experience the foliage of the Central Plains cultivars holds up very well to full summer sun and drier conditions.

Though we have been grown tree peonies for almost a quarter century here at Cricket Hill, we continue to learn so much about these fascinating plants every season. In the future we plan to recommend that customers site their P. rockii tree peonies in locations that do not receive full sun all day. This is particularity true for growers in regions with hot summers were rainfall can be lacking.

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