Archive for August, 2011

From late August to early October is the time to graft tree peonies in our USDA zone 5. Grafting is the most efficient means of reproducing a new clone of an existing tree peony variety. This is an ancient technique whereby the bud of the desired variety is fused onto an under-stock of either tree or herbaceous peony root. This nurse root serves as a ‘battery’ which powers the new growth for a year or two before it develops its own roots.

Cross section of a successfully grafted tree peony. This plant did not ultimately flourish because it was not planted deeply enough and the tree peony never developed its own roots.

One of the main reasons tree peonies remain expensive plants is that grafting, though a relativity labor intensive and slow process remains the most effective means of asexual propagation. Tree peonies reportedly can be rooted from summer cuttings, but success requires humidity and temperature to be carefully controlled. This is very difficult and not done in any production setting we are aware of. There have been some reports of success in cell tissue micropropagation of tree peonies, though large-scale success has thus far proved elusive. Age-old grafting techniques are the preferred method of propagation of tree peonies in Japan, China and the U.S.

Grafting will remain an essential skill for gardeners to propagate woody plants, as it has been for centuries. We present here a low tech method with little specialized equipment for those dedicated gardeners who seek to propagate their woody tree peonies.

Grafting tree peonies is similar to other kinds of grafting, but also differs in a few key ways. The following is the method we use at Cricket Hill Garden.

Preparing Tree Peony Scions and Herbaceous Peony Roots

Cuttings can be taken from tree peonies from late August through early October. In this period the buds have reached a good size and the stem have yet to become too woody.  Select large terminal buds for cutting. These cuttings are known as “scions”. Each scion should contain at least one terminal bud. If you can get a secondary bud as well, all the better.

Choose big terminal buds like this for use as scions.

After cutting your scion, trim off the leaves. Leave buds lower down on the branch to develop. Realize that in cutting the terminal buds, you are cutting off next years flower buds. This may be hard for any peony grower to accept, though a new tree peony may be of some compensation.

Leave secondary buds to develop for next year.

Trimmed tree peony scions.

If you are not going to do you grafting immediately, you can store the scions wrapped in a damp paper towel in a sealed plastic bag in the refrigerator. Scions stored in this manner should be viable for several weeks.

The best herbaceous roots are 2-year-old seedling which have been ‘decapitated’ of their ‘eyes’. Seedling roots are the most vital. If you do not have seedlings, a good healthy piece of root from any herbaceous peony will work very well. To obtain roots from a well established plant, you can either dig up a whole plant and cut what you need or extract a few roots by digging around the clump. For each graft you will need a 5-7” pieces of healthy and undamaged herbaceous root. Be sure that you keep track of the terminal end of the root.

2-year-old herbaceous seedling root which has been ‘decapitated’, or had its eyes cut off.

Large herbaceous root harvested from the side of a large clump. Note that we have cut the bottom end of the herbaceous root at an angle so we can distinguish it from the top

It’s best to pick and clean your herbaceous roots the day before you intend on grafting. Store them in a cool, damp place. This will allow them to become a bit less brittle and a little more elastic when you are ready to graft. Freshly harvested herbaceous roots can also be used but are quite brittle.

Tree peony roots, usually of ‘Phoenix White’ can also be used as under-stock. These are much more difficult to work with than herbaceous roots and are not recommended.

Before using your scions and roots soak them for 10 minutes in a 10% bleach solution. Then wash them off until they no longer smell of bleach, allow to air dry before begging grafting.

A quick 10% bleach bath before grafting helps to eliminate unwanted bacteria.

There are many different kinds of cuts which can be made to secure the tree peony scion to the herbaceous root. Make sure to sterilize your blades with alcohol before doing each graft. We will discuss the two which he have had good success with at Cricket Hill Garden.

Side Graft

Cut scion and rootstock at complimentary angles. Make sure that your cuts are on a level plain so that there will be good contact. The aim is to have the cambium layers of the tree peony scion and herbaceous understock match up. The cambium layer consists of the undifferentiated cells of the vascular system of the plant and is where growth occurs. In a successful graft the vascular cambia of the scion and rootstock grow together.

For a side graft, make one clean and even angled cut at approximately 45° to the scion.

Make a cut at a complementary angle on the herbaceous root.

The goal is to have the cambium layer of the scion and the rootstock match up.

Align the cambia of the scion and the rootstock.

It is not necessary to have the scion and rootstock be of the same diameter. If one is larger than the other, just match the cambium layers up on one side.

Tie up with rubber band. We use specialty grafting rubber bands, though a plain old office rubber band will also do.

Cover wound completely as possible, don’t worry if there is a bit of exposed tissue at the very top.

Wedge and Cleft Graft

This is a standard set of cuts and is perhaps an easier introduction to tree peony grafting than the faster side graft. Wedge and cleft grafting required four cuts. The goal here again is to match up the vascular cambia of the scion and the understock.

First, cut your scion with an even wedge.

Make sure that the two sides are as even as possible. We like to use a very sharp grafting knife or a  straight-edge razor blade for fast, clean cuts.

The wedge needs to have an even and clean bevel.

Then, cut a complementary cleft out of the rootstock.

Keep in mind that there is some give to the herbaceous root so the wedge should be narrower than the cleft.

The wedged scion should fit snugly into the cleft in the herbaceous rootstock.

Again, don’t worry if the scion and rootstock are of different diameters, just make sure that the cambium layers match up on one side.

Tie up the graft.  I like to tuck the tail in at the end and forgo tying a knot.

Tightly tied up.

Don’t futz around trying to get the scion and rootstock to fit just right. The Chinese say the excessive rubbing of the cut surfaces decreases the change of the graft taking. Better to practice making sharp, clean cuts before attempting grafts for the first time.

Even high volume commercial operations do not achieve 100% success in tree peony grafting. Our first year we had about 70% of our grafts come up in the spring, last year was lower, but that is because we began too early in the summer. Hopefully this year we will achieve 80-90% success.

Most tutorials on tree peony grafting have you cover the rubber band and wound area with grafting tape or polyfilm before setting aside to heal. We do not feel that this step is necessary because we heal the grafts for a short time at a high heat as opposed to a relatively longer period at room temperature.

Healing the Grafts

After you have tied up your grafts, they need to be healed. We have found the best way to do this is for a short time at a high heat. Place grafts in a 4” deep tray with clean, slightly damp sand at the bottom. The sand must not be too wet or the grafts will fail. Cover grafts with at least 1” of damp sand.

Be careful not to jostle the scions too much in fitting the grafts into a try of sand.

Keep the sand covered grafts at 90° F for six or seven days. We use a heat mat to do this. Ensure that the sand remains damp by occasionally misting the top and covering with a piece of plastic.  If the medium is too wet or too dry the grafts may fail.

We allow the grafts to heal for six or seven days.

After six days, the grafts will have ‘taken’ and the healing will have begun. We find that if the tree peony buds are still firm there is a good chance that the graft was successful.

Select a planting location which is has deep, well drained soil (pH at least 6.5) and receives about 6 hours of sun.

We use an iron breaker bar to make the holes in the garden bed  in which the grafts are planted.

Plant grafts so that top bud is 2-3” beneath the soil, space grafts 8” apart in 1′ rows.

Make sure that the graft is snugly planted with 2-3” of soil covering the top bud.

Mulch with a light layer of straw or leaves to help retain moisture. Right before or after the ground has frozen in the late fall cover your graft bed with a a layer of clear plastic and add additional mulch on top of this. We do this in November.

Mulch graft beds after planting to retain moisture. Cover with clear plastic and more mulch in the late fall, when the ground begins to freeze. Covering with plastic too early will invite mice to nest in your graft bed and ruin your results.  This has happened to us, so we warn you of this problem. Covered grafts are dormant all winter and begin to grow in the spring.

In the Spring…

Uncover your grafts by removing all mulch in mid to late March or when the crocuses bloom. The young shoots should be poking through the soil at this time.

Emergent tree peony graft in the very early spring.

Expect first year grafts to grow to 8-16”. Some may even form viable flower buds, though it is best to pick these off at an early stage so that the plant does not waste energy on a small flower. Begin to fertilize in the later spring after the leaves have turned fully green.

The amount of first year growth is contingent on a number of factors; ranging from scion and understock size to planting conditions and the relative vigor of a given variety.

This comparison illustrates the importance of using large and vigorous herbaceous roots as understock. These are both 1st year grafts of the same variety, the only difference was the size of the herbaceous root used as understock. Bottom line: the bigger the root the greater the strength of the ‘battery’.

In the fall of the first year, you may want to further space out your grafts. Space to 2′.  Remove rubber bands. If the graft has not developed any tree peony roots by this point, replant it deeper, at least 4” above the graft union.

1st year graft which has thus far failed to develop any tree peony roots. These are merely roots from the herbaceous understock.  It should be replanted above the first two buds.

                                    Grafted tree peonies which are not planted deeply enough often never

                                    develop tree peony roots and will fail to thrive.

2nd year graft with two vigorous stems. Most varieties will begin to flower in the 3rd year.


Basic tree peony grafting supplies.

Sharp grafting knife or straight-edge razors

sharp gardening snips

isopropyl alcohol (to sterilize cutting instruments)

paper towels

rubber bands or hemp twine (specialty grafting rubber bands are available from nursery supply companies, but plain old rubber bands will also do)

herbaceous peony roots

tree peony scions (bud cuttings)

tray with damp, clean sand

heat mat (not strictly required, if there are other means of keeping grafts at 90 degrees for the healing period)


‘Itoh’ or intersectional hybrid tree peonies can also be reproduced by grafting using the technique described here.

Tree peonies can also be propagated by means of root layering and division. We will be posting on these two techniques later in the fall.

In one of my first posts, I discussed experimental Spring grafting. Unfortunately all but one of these failed, though this could have been for a number of reasons. The scions were picked from winter damage and could have been dessicated, also the root stock was very small. Bottom line is that grafting is best done in the fall.

Some other links of interest on tree peony grafting

A good tutorial prepared by the Mid-west peony society.

An article by English peony grower Jo Bennison on tree peony grafting.

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Summer, in between the sowing and the reaping is a time for growing. These long, hot days can be idled away waiting for the tomatoes to ripen, or even, heaven for-fend at something so decadent as a day at the beach!  At Cricket Hill we spend the dog days of summer opening up new lands and renovating the older parts of the garden. We plan on planting peonies in these new beds, but also more vegetables and fruit trees.

Tilling up some new areas in our nursery field. It wants to be a hay field, but we have other ideas…

After removing as many of the weed roots and rocks as we can, we will augment the new beds with calcitic lime to raise the pH and Azomite to increase the level of micro-nutrients in the soil. We will then cover the bare areas with black plastic to prevent photosynthesis from occurring. The sun-starved meadow grass can then be raked before planting. Hopefully a good layer of mulch will also help keep the grass under control next year.

We harvested a fine crop of ‘Connecticut Potatoes’ from the field.

Some of our more delectable Connecticut potatoes, these are good for more than rock soup.

We are putting this new bed in an area that has a tendency to flood in the spring, so we need to make it raised. Lucky there is no dearth of stones for the new wall. Because of its proximity to a creek, the soil here is exceptionally rich, and altogether different from our usual sand and rock.

Digging out the stones from one area provide the building materials for this wall. Because of the heavy rains we receive in the spring, we always seek to plant our peonies in raised beds.

We hope that you enjoy these glorious days of summer, whether you are lugging around boulders or even lounging at the beach!

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Each year we collect seeds from our collection of Northwest Cultivar Group (rockii) tree peonies. You can order them from our website or send us $12 to receive 25 freshly harvested in late August. (Price includes postage.) We also have limited numbers of other peony seeds for sale. Please see our website for full information. Get your requests to us soon, we can only provide seeds a limited number of seeds each year.

Many of the seeds of Northwest Cultivar group p.rockii tree peony hybrids will yield plants which will produce these beautiful white flowers with maroon flares (blooming in about four years). This flower form and color is very similar to the wild species P. rockii.

Late August to early September will be the time to collect this year’s peony seeds. The vast majority of peonies yield viable seeds so if you left the pods on the plant all summer, try your hand at raising a crop of peonies from seed. Peonies raised from seed do not come true to the parent plant, though they may strongly resemble it. Almost all cultivated tree and herbaceous peonies are hybrids far removed from their wild species ancestors. The exception to this rule are seeds collected from a single species of peony which did not cross pollinate with other peonies.

Intersectional hybrid (Itoh) peonies are sterile and do not yield viable seeds. Unfortunately some garden favorites like the advanced herbaceous hybrids ‘Coral Charm’ and “Lois’ Choice’ are also infertile. Most of the European and American ‘lutea’ hybrid tree peonies like ‘Leda’ or ‘High Noon’ very rarely produce viable seeds. However, these are but a very small subsection of the peony world, the overwhelming majority of Chinese and Japanese tree and herbaceous peonies all yield large quantities of fertile seeds that will soon be ripe for the picking and planting.

Right now the beautiful star shaped pods are swelling and beginning to turn from a leathery green to brown in color. Seeds are ready to be harvested when the seedpod has turned a dark tallow-brown. We generally harvest our tree peony seeds here between the  3rd week of August and early September.

A good seed producing tree peony can yield over 50 seeds per pod.

The herbaceous seeds are ready a bit later, around the end of August.

An almost ripe herbaceous peony seed pod.

Methods for Seeding Tree and Herbaceous Peonies

When the seed pods have become a dark brown color and are just beginning to crack open, the seeds are ripe and ready to be harvested. Open up each segment of the seed pod carefully and remove the seeds. Damaged seeds will not germinate.

When fully ripe, peony seeds develop a double-dormancy which consists of a hard outer seed coat and dormant embryo. Germination occurs when air and water are able to penetrate the seed coat and reach the embryo.

There are many different methods for starting peony seeds. Some are determined by the natural condition of the seed, that is the level of dormancy while others are decided by the grower, primary weather to germinate the seeds outdoors or indoors.

Direct seeding outdoors

Freshly harvested seeds  may germinate in the same season (in the late fall) and sprout the following spring as a small green shoot above the soil. Directly planting dry seeds  with a hard and dry seed coat may need two growing seasons to naturally overcome the double-dormancy. These seeds shown below are harvested a little too soon. We have learned that it is better to wait to harvest brown and black seeds, otherwise the seeds will easily mold if not cured and somewhat dry.

Within each lustrous pearl is the germ of a peony which the world has never seen bloom, and has the potential to awe onlookers for centuries to come. Make the world a more beautiful place, plant some peony seeds this fall.

Left to mature seedpods will change to a dark brown and inside the seeds will change to black. The seedpods will also crack open. This is the time to plant the seeds.


Plant fresh (tan, brown or black) seeds directly in a sandy loam, garden soil mixed with a little extra sand, perlite or aged bark nuggets for drainage. The pH should be near 7.0, which often means adding some garden lime to sweeten the soil.  Either plant directly in a seed bed or use pots with good drainage holes, 10-12” in diameter.  We prefer clay pots or root control bags for seeding, though plastic pots will work.

Plant seeds about 1-2” apart, 2“ deep, and water well to settle in.  Seed orientation does not seem critical; the rootlet will find its way downward. At Cricket Hill Garden, we will sink the pot into the garden bed so it is protected in winter. Choose a site that is half sun, half shade. Cover over the seeds with 2-3 inches of mulch for protection from squirrels. If late summer and fall weather is hot and dry, water periodically to prevent drying. Normally, this is not needed after September in our climate. Later in fall, in late November, add 2-3 more inches of mulch for winter protection.

‘Root Control’ bags planted with peony seeds mulched for winter.

If conditions are right, the warm late summer weather will cause the seed to sprout and then cooler fall temperatures will promote root growth until the freezing weather. Nothing will show above soil level until next spring. Some seeds will not germinate until the second spring. Do not be impatient. We have given up on tree peony seed pots too soon, only to have them sprouting and growing in the compost pile! After two full years and 2 springs have past, and nothing shows, then likely you have a failure to germinate. This is often the case when you let the seeds dry out while germinating. So the first fall is very critical to have some  moisture in the seed pot.

Tree peony seeds sprouting in the early spring. These germinated in the fall.

Remove mulch from the pot in spring about two weeks after the ground has thawed, leaving pot submerged in the garden. Observe any new growth by May. Young sprouts need to be watered and fed a mild liquid fertilizer, such as Neptune’s Harvest fish-seaweed fertilizer every other month during the growing season, April to September. Young sprouts will be about 2” tall.

1st year tree peony seedlings in June.

1st year herbacoeus peony seedlings.

Move young seedlings ONLY IN THE FALL. Allow them to grow undisturbed until September of their first year.  After the first year space to about 6” apart in the garden.

In the second year tree peony seedling develop true leaves and grow to over 6” tall with foliage.

Young plants may be moved again in the fall season of their third year to a more permanent location. Allow at least 4 to 5‘ for each plant (3′ for herbaceous peonies) choosing a well drained site with 5-6 hours of sun for tree peonies. Tree peony seedlings will often start to bloom in their fourth year. While herbaceous will sometimes bloom in their third year. Keep in mind that peonies sometimes take several years of immature flowers before they show their mature form.

We have found this ‘direct’ seeding method very effective for seeds of  Northwest Cultivar group Chinese (P.rockii) tree peonies such as ‘Snow Lotus‘ and herbaceous peonies. Seeds from other hybrid groups of tree peonies may germinate more easy with the benefit of the steps described below.


Open freshly harvested seed pods as described above. Instead of opening seed pods immediately after harvesting, some growers allow the pods to cure in brown paper bag for a week in your garage or a shady, dry area. After a week, carefully open the seedpods.

Place the seeds in a zip-lock bag of slightly damp fine sand or vermiculite. Put the bag in a warm place (around 80 degrees). We use the top of our refrigerator. Root growth may commence in 4-12 weeks, after which point the sprouted seeds (identifiable by protruding white rootlet) can be planted outside as described above or put in a refrigerator for a period of cold stratification of 3 months at 40 degrees (the vegetable crisper of the refrigerator is a good spot).

Sprouted herbaceous peony seeds. These can either be planted outside if its early in the fall or put in the refrigerator for a period of cold stratification.

Sprouted herbaceous peony seeds. These can either be planted outside if its early in the fall or put in the refrigerator for a period of cold stratification.

After this point the sprouted seeds can be planted in pots and either grown under lights indoors or gradually introduced to natural sunlight outdoors.   A note of caution, the protruding rootlet is very fragile, so handle with care when planting. If seeds fail to germinate after the first cycle of hot/cold stratification, repeat the three months of warm treatment (around 80 degrees) followed by 3 months at 40 degrees.

Peony seeds which have a black or dark brown in color and have a hard seed coat. If these seeds are planted outside without any special treatment, it will likely take two growing seasons for the right combination of water, heat and bacteria to beak down the seed coat and allow water and air to reach the embryo. We recommend scarifying the seed with a file or medium sand paper. Two or three passes is all that is needed to gently rub the seed coat. See the photos below.

Without special treatment, dry, black seeds need to go through a period  warmth and winter chill (either natural or simulated) before germinating.

In order to speed germination, the seeds can be scarified. This is a method of physically breaking down the outer seed-coat. We use a rather course file.


Hold the seed between your thumb and forefinger and give it 2-3 light passes with the file.

About 2-3 light passes with the file is all that is required, filing too deep will damage the embryo. If you file the seed down to the point of the white interior, you have gone too deep. Filing so that you remove the outer seen if usually enough. It is only necessary to file a small section of the seed. A diluted solution of sulfuric acid can be used to scarify large batches of seeds.


Filing just below the shiny exterior coat is all that is necessary to allow air and moisture to reach the dormant embryo initiate germination.

After scarifying, seeds can be planted out directly if its still early in the fall and the ground is workable.

If planting indoors, follow the instructions for warm/cold stratification in the section for planting fresh seeds.

Some other considerations regarding peony seeds:

  • Single, and semi-double flowers tend to yield more seeds than complex double forms.
  • Place in cold and dry storage if you are unable to plant right away.
  • Seeds collected from single specimen tree peonies (not in proximity to any other tree peonies) may not be viable.

Some of the beautiful tree and herbaceous peonies we have raised from seed. We call them our own Peony Heaven hybrids, but really we are just stealing the credit of the bees and the wind!

‘Zhou Dynasty Yellow’ herbaceous peony

‘Peony Heaven Celestial Peach’ herbaceous peony

New and as yet un-named Peony Heaven tree peony. Bloomed for the first time in 2011.

Another new Peony Heaven tree peony.

‘Post-Modern Phoenix White’ Peony Heaven tree peony

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