Raspberry plants produce fruit on 2-year-old canes, and pruning is done each year to spur growth, remove older canes and make way for the new canes. This constant renewal and turnover process is supported by organic top dressings to enrich the growing soil along with applications of synthetic or organic fertiliser products. Fertilising, topdressing and mulching are each done at certain times of the year to be most beneficial to the raspberry plants.
Make the first application of fertiliser to your raspberries canes roughly 10 days to two weeks after they are planted in the growing soil. Use an organic or synthetic fertiliser with a guaranteed analysis of 5-10-5. Cast or pour the fertiliser around the base of each plant being careful to stay slightly away from the main stem and refrain from applying it over the top of the plants. Water well to soak the fertiliser and soil.
Fertilise your raspberry plants during their second year and each year thereafter with a complete, balanced fertiliser product with a guaranteed analysis of 10-10-10 or similar ratio. Make this application early each spring after the ground soil has thawed and before the plants break dormancy. Use 3.18 to 4.54 Kilogram of fertiliser for every 500 square feet of raspberry plantings. Cast around the base of the plants keeping sway from the trunk and main stems. Water well to soak the applied fertiliser and surrounding soil.
Top-dress the planting soil with well-aged manure each year in mid- to late spring, applying 56.7 to 90.7 Kilogram for every quarter acre of raspberry plants. Place the aged manure roughly 12 inches away from the crown or main trunk of each plant and do not till it into the soil as this can disturb the roots.
Lay down a 4- to 6-inch-thick blanket of organic mulch each fall to insulate the roots and keep weeds at bay. Use well-rotted sawdust or clean straw as they are lightweight and not prone to carry disease.
Refrain from fertilising your raspberry plants in late summer or fall as this may spur tender growth that will be killed off by winter temperatures.