Why shag is different
A high pile is a trap. Dust, grit and crumbs fall between the strands and settle at the base, so a shag rug can look clean on top while it is dirty underneath. The long fibres also tangle and shed if you treat them roughly, which rules out the stiff brushing and beater-bar vacuuming that works on a low flat rug.
Vacuum it the right way
Turn the rotating beater bar off and use suction only — the upholstery or floor nozzle — or the bar will grab the long pile and pull it loose. Go slowly so the suction has time to lift grit from the base, work in both directions, then flip the rug and vacuum the back to shake soil down and out. Do this often; it is the main way a shag rug stays clean.
Shake and air it out
For a smaller shag rug, take it outside and shake or gently beat it over a railing to knock out what the vacuum left behind, and let it air. A good shake moves surprisingly more dirt than another vacuum pass once the base is loaded.
Spot-clean spills down to the base
Blot a fresh spill with a clean white cloth, parting the pile so you reach the spill at the base rather than smearing it across the tips. Work from the edge inward with cool water and, if needed, a little mild detergent, blot it dry, and let the spot dry fully before you walk on it. Do not scrub — scrubbing mats and tangles the pile.
When to leave it to a professional
A deep clean is where shag gets hard at home: the dense pile holds water, is slow to rinse clean and takes a long time to dry evenly, which risks mildew at the base. For a full clean, a plant that can flush the rug through and dry it under controlled airflow does what a home clean cannot. Check the fibre first — a wool or silk shag should go straight to a professional.