Raspberries are generally easy to grow. The vines these plants produce can grow to 6 or 7 feet long and need some support in the form of a trellis or arbor, so plan ahead before you plant a vine or two. You can choose between chemical fertilizer and one with organic origins, such as compost or worm castings. Proper fertilization will ensure that you get the maximum harvest of the largest, juiciest berries.
All plants need this essential nutrient in order to develop healthy green foliage. Give your raspberry plant a high nitrogen fertilizer when it begins sending out new growth in spring. As soon as you notice flower buds starting to form, switch to a lower nitrogen plant food, such as one having an N-P-K ratio of 4-20-20. Apply it according to label instructions once a month until mid August.
Organic Fertilizer Mix
You can feed raspberry plants with organic fertilizer and expect a good harvest later in summer. If you make an organic fertilizer mix, apply about 1 cup of it to the soil around your plant once every two weeks, taking care not to allow it to touch the plant. When blossoms begin to form, reduce the amount of canola seed meal or fish meal by half (using two parts instead of four) and continue applying it to your plant until mid August. Mix together the following ingredients in a container large enough for the amount you plan to make: four parts fish meal or canola seed meal, one part dolomite (lime), one-half part bone meal and one part kelp meal.
Sulfate of Potash
If you spray the foliage of your raspberry plant with an organic fertilizer containing sulfate of potash, it will benefit from the increased soil fertility due to the concentration of potassium in this product. Mix 1 to 2 oz. of sulfate of potash to each gallon of water and spray the foliage every other week. GrowOrganic.com recommends using 1 lb. of this natural substance for every 100 square feet of growing area.
Well-composted steer or chicken manure will provide your raspberry plant or plants with smaller amounts of the essential plant nutrients nitrogen, phosphorus and potassium than chemical fertilizers, but all of it is readily available to plants. Chicken manure contains an N-P-K ratio of 3-2.5-1.5 to 6-4-3 and steer manure is lower, at 1-1-1. If you mix animal manure with your other fertilizer, or purchase a plant food containing an animal manure, your raspberry will get the nutrients it needs. You can also use worm castings, which are the manure that compost worms produce. Combine 1 cup of worm castings in 1 gallon of water and use it on your raspberry plant to give it nitrogen, phosphorus and potassium in the ratio 3.2-1.1-1.5. Because worm castings are relatively high in nitrogen, do not use them after your raspberry begins to flower.
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