Waste areas like this are suited to mass plantings. Mass planting helps prevent overgrowth of pest plants. Extra effort is required to get plants established in these situations. Use careful weed spraying and/or line trimming around the plants or circles or squares of biodegradable weed suppression matting such as coir or jute with a slit to the centre with a suitable sized hole, put these around the trunk with the previously mentioned weed control methods used in between if required, we have used this system a lot because maintenance until establishment for the customer is much easier.