In the process of removing invasive plants the question arises, what to do with the plant material containing viable parts. To prevent reestablishment and spread of the species this material must be properly managed. The best time to remove invasive plants is before plants flower and produce seed. Seeds can lie dormant in the ground for decades until conditions such as soil disturbance, light, temperature, and precipitation are such that the seeds have an opportunity to germinate. It is important to routinely monitor the site cleared of invasive plants until desirable and durable native species become established to out-compete the invasives.
Invasive annual and biennial flowering plants: Timing is critical to successfully control invasive plants. In many cases once a plant flowers or bolts it will produce seeds even if the plant has been uprooted but left on the ground or even composted. The annual mile-a-minute, and garlic mustard, a biennial (meaning the plant lives for two years before it produces seed in the second year prior to dying), typically invade Long Island soils. The best time to uproot these and similar plants is as small seedlings before evidence of flowering (in the first year for biennials). These uprooted seedlings can be left on site or composted. Check for new growth weekly, and flowering stems must be uprooted, solarized and disposed.
Solarize the plant waste by placing the stems, flowers and seeds in clear plastic bags and store in full sun. Black bags smother plants by excluding visible light so the contents don’t gain as much heat, but they do stop photosynthesis, which kills the leaves but not the seeds. Tie and place the clear bags in the sun to trap solar radiation until the seeds have cooked, which generally takes place at 125 F degrees — although temperatures and time varies by species. This process may take a month or two before the wilted plants can be safely disposed.
Invasive Perennials: Perennial plants, including small flowering plants and grasses, are capable of out-competing native plants. Since these non-woody herbaceous plants die back yearly to return in spring from their root-stock, the roots/rhizomes of plants such as Japanese knotweed must be uprooted prior to seeding to prevent the plants from spreading. Pull or dig up roots and bag the stems, flowers, seeds and roots/rhizomes. Solarize as above until the roots/rhizomes have wilted. Some flowers and seeds remain viable once pulled, and should be bagged immediately, solarized and disposed.
Invasive Trees, Shrubs, Woody Vines: Prior to flowering, seedlings and saplings can be pulled and left in place with roots exposed to dry. The larger material can remain on site as a brush pile but should be flipped or turned occasionally to expose roots at the bottom of the pile. Once dried, the wood can be chipped for mulch or composted. If removed during or after flowering occurs, cut out the flowers, fruit and seed parts, and dispose. Do not home compost or leave on site. Some vines and seedpods such as wisteria and porcelain berry stems remain viable once pulled, and should be bagged immediately, solarized and disposed.