Hi Lauren, Tui do not recommend blended or granular fertilisers for pots and containers because the fertiliser does not have a control mechanism and so there is a greater risk of burning plant roots if over applied. When used in the garden the soil acts as a buffer and disperses the fertiliser. If over-applied to a plant in a pot, the  fertiliser accumulates at the pot wall and can cause burning of the roots. The best fertiliser to use for pots and containers is Tui Enrich Rose, Camellia, Azalea, Gardenia controlled release fertiliser. It might seem like an unusual recommendation but blueberries prefer acid soil conditions as do roses, camellias, azaleas and gardenias. The alternative is Tui Enrich Citrus & Fruit controlled release fertiliser. Controlled release fertilisers release nutrients when plants are actively growing as they are dependent upon temperature and moisture to work, too hot or too cold, the fertiliser is not released, likewise if there is no moisture present. If a person has already purchased the product and it is inconvenient to return to a store to swap the product, use half the recommended rate for pots, but apply on the side of caution.