Fertilization of raspberry plants aids with vigorous growth and fruit production. The application of fertilizer and possibly additional nutrients is essential.
Best Growing Conditions...
Sun - The best and most berries will be produced when raspberries are planted in an open site that receives at least 6 to 8 hours of sunlight. The best and most berries will be produced when blackberry plants are growing in full sun.
Soil - Raspberries will grow reasonably well in most soil types except for very compacted clay or light chalky soil. In these soils it'll be worth your time to mix in lots of organic compost to condition the soil and add beneficial nutrients and bacteria plants need to grow healthy. Raspberries grow and produce the best fruit in well-drained, moist and fertile soil that is rich in organic matter. They like the soil to hold a good supply of water, especially when the fruits are developing in summer, but not so much water that the soil stays constantly soggy or wet. Plant raspberry bushes on ridges or in raised beds if drainage is a problem.
Soil pH - Raspberries do best in an acidic soil between 5.8 and 6.5 on the pH scale. It's a good idea to test the soil for pH. Testing kits are available at most local nursery and garden centers or you can buy soil test kits online here. Your local Extension Service might provide soil testing services as well. Depending on the results of the soil test, you can add lime to raise the pH or soil sulfur to lower the pH (make more acid).
NOTE: Avoid planting raspberries within 300 feet of any wild blackberry or wild raspberry plants and in areas where tomatoes, potatoes, or eggplants have been grown previously.
When To Fertilize Raspberry Bushes
When you fertilize will depend on the type of raspberry and the type of fertilizer you are using. If you are using an organic plant food or composted manure these can be applied in early winter. But wait until late winter or early spring if you are using an inorganc fertilizer such as 10-10-10.
Fall-Bearing Raspberries
Fall-bearing raspberries are a special case. They will need an extra boost of fertilizer in the fall. This is in addition to the regular fertilization schedule. Wait until you see blooms on the new canes and apply 1 to 2 pounds of ammonium nitrate for every 100 row feet of raspberries you are growing. You can also use ammonium sulfate at a rate of 1.5 to 3 pounds per 100 row feet.
How To Fertilize
First Spring on New Plantings
When primocanes emerge in new plantings, scatter 1/4 cup ammonium nitrate (33-0-0) or cottonseed meal at rate suggested on the package around each plant. Avoid dumping fertilizer around the base of the plant. Instead, scatter it evenly around the plant.
Thereafter
Once the planting is established, fertilize yearly in late winter or early spring. Evenly distribute fertilizer such as ammonium nitrate (1/5 cup) or 10-10-10 (1/2 cup) per plant. Alternatively you can use an organic plant food or mulch around plants with an organic compost at rates recommended on the label. Do not apply all fertilizer at the base of the plant, but spread it over the entire area.
Boron Deficiency
Boron deficiency in raspberries can produce lower yields and smaller fruits. If you suspect your raspberry plants are suffering from a boron deficiency, a tissue test of your plants must be conducted. Find the nearest lab by contacting your local extension office or the agricultural department of a local university. If tests determine that your plants are suffering from a boron deficiency, boron additives are available at nurseries as a foliar spray. An application of boron when none is needed is detrimental to crop production. You must not add this nutrient to your plant unless you have first conducted a tissue test.
Mulching
Raspberries benefit from mulching. Good mulches for use in the home garden include leaves, lawn clippings, and wood chips or shavings, because they are usually free of weed seeds. Pine straw or shredded wood or bark products work good as well. If you are making your own homemade compost, add 1/4 to1/2 cup of ammonium nitrate per bushel of wood shavings or compost material to speed decomposition and protect against nitrogen deficiency in the plants.
