Removing Goldenrod rhizomes and plant roots



I am a novice gardener and have had a rough work schedule the last few years and have not kept up properly in the garden.

Goldenrod took over in my garden where there had been a 8×10′ patch of through which a stone path wanders. The goldenrod, in dry conditions grew extremely tall and stood upright most of the summer season and if I am honest some cut back the earlier year grew even hardier than the newest plants. In September/October the plants were cut to ground level and the debris taken away though some seeds were dispersed from pods and I expect there are rhizomes and strong roots underground. I missed digging out the roots in October due to work and a sore back. Now it is November and the temperatures are dropping (around 2-5 C at night), however my back is good and I am unsure how to proceed for the winter.

Where I live the soil is a bit sandy. I do not know if it is alkaline or acid or neutral – no soil tests done.

The goal next summer might be to have a hearty lawn again around these stones, perhaps with some other plants.

There is sign of moss in some areas of the garden where it is damp and shady and exposed.

There are worms visible in the top few inches of soil.

Frost has likely come once, but temperatures at night will be above 0 for maybe 2 more weeks.

Winter is generally partly grey/wet/cold and partly snowing with snow layering up to 20-30 cm.

Surrounding this area there are flagstones and the site’s rain runoff will naturally flow over this area.

I have a few above 0 C days now in November and have a tiller and shovel and pitchfork and trowel and weed removal tool and energy and motivation.

My options to fully get rid of this goldenrod (an admirable plant in many respects, but not desired in this location) *seem* to be… (thank you Master Gardeners, Landscape Ontario, City staff for your web sites!):

RE: Roots and soil
(a) Leave the roots until spring – with frost, it would be better to keep the ground compacted and not risk seeds getting deeper into the ground
(b) Dig out the roots ASAP – cold weather be darned.
(c) Dig out the roots and turn the soil and though it is late mix in leaves, green waste, manure, and/or compost matter
(d) Do something [?] to compact the ground so that it doesn’t erode in run off at spring thaw and provide covering matter [?] for bugs and wildlife to hibernate/feed

RE: Regrowth prevention for the next 10-12 months
(e) Cover the ground with cardboard secured with pegs, mulch and rocks
(f) Cover the ground with opaque black gardener’s cloth secured with pegs, mulch and rocks
(g) Cover the ground with black plastic sheets or tarp secured with pegs, mulch and rocks
(h) Cover the ground with clear plastic secured with pegs, mulch and rocks


0) What combo of options a-h above would you recommend? Or something else?

1) I am not clear what is the risk/benefit of digging up the roots now versus in the spring.

2) I am not clear what is the risk/benefit of turning the soil now versus in the spring.

3) I am not clear what is the benefit of cloth/cardboard covering up the ground now or in the spring.

4) I am not clear on what ground cover technique is best in terms of effectively killing the Goldenrod roots while managing moisture correctly and for a best impact on the worms, etc… (there are no other plants of concern)

5) I am not clear for how long to cover the area though understand that a period through the hot summer months might be warranted to restrict ‘sun and water=food’ to the plant and to apply heat to the plant roots and rhizome matter and any seeds not visible but possibly in the soil

6) I am not clear on whether the GoldenRod rhizomes or miscellaneous seeds can even be ‘killed’ at all as I think these might be quite hearty and designed to endure harsh conditions so they will require a dig out ultimately.

7. The ground is somewhat flat with a slight 5-8 (max) degree incline. What is the risk if the roots are dug out and there is nothing on the ground surface to prevent soil erosion?

I was told by a city gardener to dig up the roots in the fall and to cover up the area with opaque layers of black gardening cloth and just close up the garden normally — I don’t think he meant me to do it in mid-November.

I see value in different approaches, but there are a lot of things one could think about… Bear in mind I am a novice and there are no major risks here – just an anxious mind with questions.

What would you as a Master Gardener recommend and sorry for all the questions – they capture my best understanding of the various recommendations that people have kindly recommended.

And if this is one for a professional gardener, please advise and I will seek out someone at Landscape Ontario – just sort of rushing, because frost is coming fast! :)

With much respect and thanks,



Thank you for contacting the Toronto Master Gardeners. As you know, goldenrod which was once considered a pesky weed, is now being enjoyed as an excellent choice for a pollinator garden as it is both host and food source to a wide array of insects, moths and caterpillars. It is a native perennial, that spreads by both seed and rhizomes and is much less invasive in sunny, dry locations. I personally cannot get enough of this late summer bloomer.

Clump forming goldenrods, such as Stiff goldenrod (S. rigida) are less quick to spread than rhizome varieties and cutting back your goldenrod during the beginning of July not only extends the bloom time but will encourage more compact plants with less height.

One way to get rid of weeds and seeds is to starve them of the light they need for photosynthesis (to make food). There are a number of ways this can be done. The first is by covering the beds with cardboard, thick newspaper layers (don’t use cardboard or newspapers that are highly coloured, as the inks may not be healthy for the soil), or thick ground-cover fabric and cover these in turn with a thick layer of mulch. The covering may have to be kept in place for a whole year. There is some discussion in the horticultural field regarding the use of newspaper and cardboard and you can read more here.  These products are typically covered by some kind of organic mulch to prevent the cardboard or newspaper blowing away and to aid in their decomposition.

Alternately, you can use either black tarp (occultation) or clear plastic film (solarization); both will work, as they aim to kill weeds using different means. The black plastic method of weed control works by starving the weeds:  they cannot produce food through photosynthesis and eventually will exhaust their food supply and starve. This method takes time and will only work as long as no light reaches the plant. The University of Minnesota article on Using the Sun to Kill Weeds and prepare Garden Plots gives detailed instructions on this technique.

The clear plastic technique of weed control eradicates weeds by solarisation i.e. subjecting weeds to lethally high temperatures. This method works during a hot period of the year and when the soil will receive the most direct sunlight. In addition, solarization stimulates the release of nutrients from organic matter present in the soil. It is especially effective for treating garden soils, where the intent is to plant vegetables, herbs, and flowers.

According to the University of California Integrated Pest Management article on Soil Solarization for Gardens & Landscapes:

“The method involves heating the soil by covering it with clear plastic for four to six weeks during a hot period of the year and when the soil will receive the most direct sunlight. Plastic tarps allow the sun’s radiant energy to be trapped in soil, heating the top 12 to 18 inches to temperatures lethal to a wide range of soilborne pests; including weeds, plant pathogens, nematodes, and insects. When properly done, the top layers of soil will heat up to as high as 140°F, depending on the geographic location. Soil moisture is important in this process, as wet soil conducts heat better than dry soil. Moisture also makes soil pests, weakened by the heat, more vulnerable to attack by beneficial soil microorganisms during and after treatment.”

This process will require approximately 4-6 weeks of exposure to full sun during the summer.

Whichever method you choose “Moisture is a key ingredient for weed seed germination, so watering before installing your tarps will improve performance. Water until the soil is moist down to about 12 inches before adding tarps. One key principle of solarization and occultation is preventing water from reaching the soil after the initial irrigation. So these methods will be less effective in low spots that receive significant drainage, and where water can enter underneath the tarp from the edges.” – University of Minnesota

My suggestion would be to leave the clump of goldenrod in its place for now, this will prevent any erosion which may result from snow melt in the spring and the stalks will provide habitats for beneficial insects and other creatures living in them. See Six Reasons to not Clean Up the Garden this Fall.

Cutting down and removing dead plant stems too early in the spring will disturb many beneficial insects before they have a chance to emerge. See Spring Clean Up done Right. Once the temperature has been 10C for at least 7 consecutive days you can dig out your clump of goldenrod along with as much of the rhizomes as possible. Then cover the moist area with whatever method you prefer.

Good Luck