This grant was supported by the ASCFG Research Fund. To see how you can apply for an ASCFG Grower Grant, go to www.ascfg.org and click on Research Activities.

Weed Control Methods for Field-Grown Peonies

Rita Jo Shoultz, Alaska Hardy Peonies/Fritz Creek Gardens, Fritz Creek, Alaska

I received an ASCFG Grower Grant to study weed control in peonies grown for the cut flower market. Where to begin? First of all, I’m a long way from having any solutions to the weed problem. I have learned a lot and discovered everyone growing peonies here in Alaska have a weed problem. Although many are different than my ‘special’ weeds, everyone thinks theirs are ‘special’ too. I’ve also discovered that weeds don’t mean the end. Tolerance is definitely a consideration.

My biggest weed problem is Equisetum, commonly known as horsetail. Horsetail is one of man’s oldest plants and ranks right up there with cockroaches for survival. I’ve personally dug roots up to 3 feet deep and saw no end.

Before I begin my tale of woe perhaps a bit of background on what’s happening with Paeonia in Alaska. As early as 1998, our Alaska University, Fairbanks started getting indications there might be a niche for Alaskan-grown peonies for the cut flower market. It became obvious quite quickly that peonies grown in Alaska would bloom when others in the rest of the United States were not commercially available and, due to our extreme cold temperatures in winter and cool summers, the quality and color of our cuttings were superior to those in warmer growing areas. Flash forward to 2006 when several growers started planting for the market.

Today a formal organization, the Alaska Peony Growers Association, is off and running with 84 members. There are 14 farms with approximately 33,000 plants now in the ground. Four farms harvested cuts from 3- and 4-year-old plants in 2009.

While our University has done small-scale research on varieties, diseases, harvesting etc., we have no history or experience for the overall growing industry. I foolishly thought with my background in the greenhouse business and with my 16 display gardens, I could grow on a large scale for the cut flower market. I have a new respect for farmers in a big way. My confidence level went from I can do this to no way can I do this to I think I can do this with a lot of hard work. I worked at Omeo Farm in New Zealand, visited Adelman Peony Gardens in Salem,Oregon, and most every other grower on the West Coast, Canada and of course have attended the ASCFG meetings to network with other growers. I’ve learned how much I don’t know. But I’ve also learned enough and met enough folk that are more than anxious to help; I think Alaska is going to do just fine.

The first two years my weed control was to actually dig up the horsetail by hand. Since I have a crew for Fritz Creek Gardens, I could steal them away to spend some time in the field. I discovered after two years the stems themselves were a bit smaller, but there were many more actual plants. I labeled this experiment ‘pinching’. Just like pinching our baskets to encourage side buds, because horsetails have such deep roots, digging up the tops and a few inches of the root were only encouraging ‘side buds’.

As an experiment, we tried corn gluten on 3 row, without success. First of all, when the gluten began to breakdown, the smell was terrific. Secondly, while there may have been some effect on seed germination, it certainly did nothing for the horsetail. These three rows had diminishedpeony production later, compared to untreated rows. Whether it was the corn gluten or other factors has not been determined.

The next plan was chemicals. We used a mix of Gallery® and Simaflow® and applied per label instructions in the spring as a pre-emergent. Timing of application can be a challenge in Alaska. We have frozen ground forever then suddenly, we have spring. Catching the window before the plants emerge and after some thawing takes place can be very narrow. We’ve resorted to using Dixie cups or compost to protect early emerging vegetation when our timing is a bit off.

The control row that had no application of chemicals had very little horsetail, while the rows with chemicals applied flourished with healthy horsetail. We had several ‘expert’ opinions as to why this happened, including the possibility that the pre-emergent lowered the pH. Could our efforts the previous fall of cutting the horsetail back been effective? Did the pre-emergent ‘feed’ the horsetail in the spring defeating our fall efforts? Only time can answer these questions as we continue our different trials.

In an area not planted and never to be planted, we tried Crossbow® to kill the horsetail. We found this did indeed kill the horsetail but also had residual effects that contaminated the soils for at least 2 years, the extent of our experiment to date. Tom Jahns of CES feels it will remain in the soils for many years and probably render the area not farmable. 2,4-D also has residual traits.

After three seasons of cutting a grassed area with a lawn mower, we found significant success in eliminating horsetail. We’re trying for the same effect with a stirrup hoe in the fields cutting the horsetail just at the surface. First indications are this weakens the horsetail and causes a slowdown in production.

We tried covering a non-planted area with black Typar (woven landscape fabric) for two seasons. When the Typar was removed, the roots were still visible and started to sprout when receiving light. The Typar allows water and air, and perhaps using a nonpermeable black plastic would have rendered different results however, we would have to do that in a non-planted field and wait for a significant time that doesn’t fit with our program.

In our display gardens, we have paths Typar lined with 8-10 layers of newspaper that have been down for 10 years. When uncovered, only a very few horsetail roots were visible. Keeping that in mind, this fall after the peonies were cut back for the winter and we could feel the stems through the Typar to know exactly where to burn the holes for our 3-year-old plants, we covered 15 rows planning to keep the Typar down permanently. We had been considering this option for quite some time but the impetus to make that decision was influenced by Ed Pincus’ presentation at the 2009 ASCFG Conference. On some parts of the field we lined under the Typar with 7 or 8 layers of newspapers and other areas used a second layer (underneath) of Typar.

We applied a generous sprinkling of Sluggo® around the peony stems and also baited for voles under the Typar. We will mulch with straw when the ground is completely frozen. Mulching before freeze-up encourages vermin to establish their winter homes. Weeding by hand allows you to get up close and personal with these wonderful plants. We’ve noticed the buds are much closer to the surface than originally planted indicating some heaving. And while we have mulched in the past with little results, because of the heaving, we will try it again this year.

It’s not all bad. Although what I consider a very serious weed problem, it doesn’t seem to affect the growth or blooms of our peonies. And when I dug up some plants to move them, the horsetail roots that were dead in the ground seemed to aerate the soil quite nicely. I know, I know. Stay tuned for the continued Alaska peony growers’ efforts.

Rita Jo Shoultz, with her husband Leroy, son Shannon and his wife Dee own and operate Alaska Hardy® Peony on their 24-acre farm. Rita Jo has operated Fritz Creek Gardens for 13 years, offering over 500 varieties of perennials, trees, shrubs, vines and roses to gardeners and garden designers in Alaska.