A method for horizontal installation of a blade of a horizontal axis wind turbine, the method comprising - providing a nacelle for the wind turbine, and a rotor hub mounted to the nacelle, - mounting a blade guide device to the nacelle, - providing a lifting means configured to suspend a blade and lift the blade to or from the hub, - supporting the entire weight of the blade with said lifting means, - moving the blade towards the hub by means of the lifting means, while the entire weight of the blade is supported by the lifting means, - bringing, while the weight of the blade is supported by the lifting means, the blade and the blade guide device into contact with each other, and - bringing, with the blade and the blade guide device in contact with each other, the blade into a mounting position in which it is fastened to the hub, wherein the blade extends longitudinally between a blade root and a blade tip, and the support of the blade by the lifting means is done by means of an engagement device of the lifting means, the engagement device engaging the blade in a region between the blade root and the blade tip, wherein a region of the contact of the blade guide device with the blade is, compared to the region of the engagement of the engagement device, closer to the blade root, - characterised by, after the blade and the blade guide device having been brought into contact with each other, supporting the weight of the blade by both the lifting means and the blade guide device comprising, after bringing the blade and the blade guide device into contact with each other, lowering the engagement device and/or shifting the lifting point of the engagement device towards the blade tip. - providing a nacelle for the wind turbine, and a rotor hub mounted to the nacelle, - mounting a blade guide device to the nacelle, - providing a lifting means configured to suspend a blade and lift the blade to or from the hub, - supporting the entire weight of the blade with said lifting means, - moving the blade towards the hub by means of the lifting means, while the entire weight of the blade is supported by the lifting means, - bringing, while the weight of the blade is supported by the lifting means, the blade and the blade guide device into contact with each other, and - bringing, with the blade and the blade guide device in contact with each other, the blade into a mounting position in which it is fastened to the hub, wherein the blade extends longitudinally between a blade root and a blade tip, and the support of the blade by the lifting means is done by means of an engagement device of the lifting means, the engagement device engaging the blade in a region between the blade root and the blade tip, wherein a region of the contact of the blade guide device with the blade is, compared to the region of the engagement of the engagement device, closer to the blade root, - characterised by, after the blade and the blade guide device having been brought into contact with each other, supporting the weight of the blade by both the lifting means and the blade guide device comprising, after bringing the blade and the blade guide device into contact with each other, lowering the engagement device and/or shifting the lifting point of the engagement device towards the blade tip.