Guardian: Dell is still finding it an uphill struggle to persuade its customers to take part in its “Plant a Tree for Me” scheme. Under this plan, customers can choose to spend an extra £1 per notebook or £3 per desktop to offset its estimated carbon emissions for the next three years. Only 300,000 customers opted to pay the levy during Dell’s last financial year, which ended in February, said Tod Arbogast, the company’s director of sustainable business. Though he declined to enumerate it, that …