The Garden Grumps
Episode 1: Mulberryweed and Solarization
That pesky little plant that seems sweet at first, but once you get to know it, there’s no going back to happy thoughts about it.
Mulberryweed (Fatoua villosa) made its way to North America from East Asia in the later half of the 20th century. It hasn’t been here long, but it travels incredibly fast. It is found in most states east of the Mississippi River and is our number one focus for weeding in the summer.
At first glance it looks very delicate and even kind of pretty, but if you don’t get it out fast, it will quickly take over! Flowers form almost as soon as the plant emerges (usually at the time of the third leaf growth) and seeds develop not long after that. Each plant produces hundreds of seeds, which take less than 30 days to germinate. Most seeds will fall below and around the mother plant, but they can also be flung up to 4 feet and can be carried by wind and water.
This invasive plant prefers moist, shaded areas, so check around the base of your desired garden plants. It is very common to find mulberry weed in nursery stock. To help prevent the spread of it, and other invasive weed species, it is a good practice to discard the first inch or two of soil in any purchased potted plant.
The one good thing I have to say about the mulberry weed is that it doesn’t tend to fight when you pull it. It is a soft plant- no stickers or thorns- and has a sturdy taproot, so usually just a firm grip at the base of the plant will pull it up, root and all… BUT watch where those flowers fall! Even if the seeds have not yet ripened, if the flowers are left on the ground, they could create new plants soon. If you put the weeds with roots and seeds straight into the compost pile, they will resprout and take over.
Herbicides can be used, but here at BHF we prefer the good old-fashioned, sustainable method of hand pulling. For larger patches, we use the tractor and Rogue Hoe to scrape the top layer of soil and remove as many weeds as possible, then suppress what’s left with brown paper and mulch. This will also help build the soil for future planting. This method is most sustainable if you use recycled cardboard boxes (remove any tape and don’t use the ones with the plastic glaze on them), recycled paper grocery bags (although you might need a lot), or if someone you know has had a home renovation, they may have left over ram board (this is best because it is the thickest).
You can also purchase ram board or rolls of painter’s paper at your local hardware store. Recently, we applied this method to treat a large patch of mulberryweed and other invasive weeds behind the farmhouse using recycled ram board leftover from my kitchen remodel and newly purchased brown paper (we use two or more layers of the brown paper because it is thin). The brown paper is sometimes called butcher paper, but be sure not to use anything with the plastic glaze.
Putting mulch on top of the paper will help with weed suppression by denying the weeds light and help build healthier soil. We like to use shredded mulch for suppression because it compacts better and creates more of an obstacle for weeds to grow through. We usually spread the mulch 3-6 inches deep. Do not use colored mulch (brown, red, black) as it is dyed and the chemicals used are not necessarily eco-friendly. Avoid Cypress mulch as well because of the host of problems involved in its production and stick to hardwood or pine mulch. This is not a fail-safe method of ridding all the weeds, there will always be a few strong ones that pop through, but it greatly diminishes the amount of weeds, and makes it easier to hand pull them when they do pop through.
We use mulch that is at least 6 months old (meaning it has been sitting in a pile in a lot somewhere for at least six months since it was run through the chipper), because mulch decomposes and gets hot as it breaks down. The newer it is, the hotter it is, and also the farthest from becoming soil. The movement of the load of mulch and the disturbance of raking it out will also create heat, especially if it gets wet, so it is a good idea to wait another 6 weeks or more before planting in your new mulch bed. Waiting will also ensure the mulch is well on its way to becoming soil. If you have the time and ability you can add some compost and fertilizer to the mulch as you lay it. This will increase its rate of decomposition and add nutrients to your new bed. Essentially you are making a compost pile right where you want to plant.
If possible, leave the pulled weeds in the sun or put them in a plastic bag to solarize them. Solarization is the process of magnifying the sun’s natural heat to kill the weed seeds and roots. For our larger patch we laid out a tarp to pile on the pulled weeds. The tarp is used as a barrier so any live roots or ripe seeds do not have access to the ground to regrow. Keep in mind that whatever vegetation the tarp is on will die as well (you can use this to your advantage by increasing your solarization space while decreasing the area to weed). If you have access to a solid concrete pad (patio, driveway, etc.) this can be used so you don’t end up with a dead patch in your yard.
After the weeds were piled on the tarp, we covered the weeds in black plastic sheeting to encourage a faster death rate. We have found that black plastic is best for solarization because it is best at trapping the heat and does not quickly break down. White or clean plastic can also be used, but in our collective experience black plastic is best; the thicker the better. White plastic is blinding in the sun and does not attract as much heat, and the clear plastic tends to degrade too fast and leave trashy plastic strips around your garden/yard.
Depending on the size and location of your weed pile, solarization usually takes a few weeks to work, generally 3-10 weeks. To speed up the process create your pile in an area that gets a lot of direct sun throughout the day and use landscape staples or rocks and bricks to hold the plastic down and restrict airflow. After the solarization is complete, there will be no live plant matter left. The dead plant matter can then be added to your compost pile as carbon.
So, all in all, weeds are pesky, but not something to get grumpy about. With a little foresight, planning, and work you can use the weeds to your advantage. Through solarization, composting and mulching, Mulberryweed and other invasives can be turned from a nuisance and a landscape liability into an asset in the form of carbon for your compost if you use some elbow grease, sunlight and patience to cook it down.