If you have bindweed (Convolvulus arvensis) growing in your garden, be prepared for a battle to get rid of it. It spreads by massive networks of roots as well as by setting seed. Vertical roots can extend 4 feet deep in the soil. Horizontal roots along the soil surface run about a foot deep and continue indefinitely. Attempts to remove the plant can actually make it grow stronger. Any piece of root that remains in the soil will create a new plant. Any seed that is exposed to light will grow a new plant. Despite these dire facts, you can eradicate bindweed with some understanding of the physiology of the plant and a good dose of diligence.
Cut the plants back to a few inches three or four times during the growing season. This causes the plant to put its energy into regenerating new top growth rather than strengthening its network of roots. Make the last cut no later than August 1. If the area is too large for this to be feasible, you can still succeed with the rest of the process. It just may take multiple treatments.
Apply a non-selective herbicide with the active ingredient glyphosate at the end of the growing season, around September or October. By this time, the plant is weakened from the repeated pruning and it is getting ready to store its reserves in the roots for the winter. This is the perfect time for glyphosate to be most effective. Glyphosate works by the foliage absorbing the chemical and sending it to the roots, where it eventually kills the plant.
Mix a solution following label directions in a plastic spray container (if spraying) or wide-mouth jar (if you'll be applying the poison by hand). Do not deviate from the recommended dilution. Stronger doses can backfire, causing the foliage to burn before the chemical travels to the roots.
Spray the solution thoroughly on the bindweed if there is enough clearance that no over-spray will touch adjacent plants. You must avoid glyphosate making contact with any of your garden plants, as it will kill them. If the bindweed is in close proximity to desirable plants, you can use a foam paintbrush to apply the solution carefully to the bindweed foliage. Watch out for drips. Another method is to put on a tight-fitting rubber glove (latex or similar) covered by a cotton glove. Dip the gloved hand in the herbicide solution and rub your fingers across the top and underside of the leaves. A more labour-intensive method would be to temporarily move your garden plants to a holding area while you treat the garden bed. If so, be sure to wash the roots and soil of the desirable plants thoroughly to make sure you do not transport any bits of bindweed to the holding area.
Expect that plants adjacent to the bindweed may possibly be damaged even if you do not get any glyphosate on their foliage. If the bindweed roots are heavily intertwined with desirable plants' roots, there could be some chemical translocation from one plant to another.
Repeat the following year if necessary.
Monitor the cleared area for new seedlings indefinitely, and hand-pull them out when you spot them. Any time you plant or disrupt the soil, there is a chance a newly exposed bindweed seed may germinate.
In open areas where you can safely spray herbicide, be sure to do it on a calm day when there is no wind. Place a cardboard barricade between the bindweed and any desirable plants. If you're painting the glyphosate on the foliage with a foam brush, put newspaper under and around the bindweed to help protect surrounding ornamental plants from herbicide drips. When purchasing glyphosate, you will find it comes in ready-to-use dilutions and also concentrate. If you have a large area to do, the concentrated form will generally be more economical. Compare the percentage of active ingredient across different brands to determine the best value.
Do not attempt solarisation (smothering the ground with heavy black plastic) to eradicate bindweed. Bindweed will continue to grow its root system as the plants search for the edge of the plastic to find the light. Do not till the soil. It will expose seeds and root fragments that will generate new plants.