In general, blackberry bushes are not heavy feeders and do not need much fertilizer after they are well-established. Too much fertilizer can stimulate wood and leaf growth rather than fruit production. Moderate amounts of fertilizer during the first and second years after planting will help stimulate young plants to size up for earlier fruit production. 

I always go the organic route when feeding any plants that will end up on the dinner table. Organic methods obtain the best blackberries possible, with the fewest detrimental effects on the environment, and their grapes reflect that dedication to quality. 



Evaluate Soil


Before you feed your grapevines it's always a good idea to evaluate soil conditions.


Soil Type Preferred

Blackberries 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. Blackberries grow and produce the best fruit in well-drained but moist 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.


Soil pH is Important!

Blackberry plants grow best in a moderately acid to neutral soil ranging between 5.8 to 6.8 on the pH scale. Most average garden soils fall between a pH range of 6.0 to 7.0. 


Testing Soil pH  

Soil pH is a measurement of the alkalinity or acidity of soil and is measured on a scale of 1-14, with 7 as the neutral mark. Any measurement below 7 indicates acid soil conditions, and anything above 7 indicates alkaline. If you're unsure about the pH of your soil, or whether or not it is suitable for growing Blackberry plants, it's a good idea to test the pH in the planting area. You can quickly test soil pH with an inexpensive soil pH tester probe. To raise the pH (make more alkaline) you can add pelletized limestone to the soil. To lower the pH (make more acid) you can apply Soil SulfurAluminum Sulfate, or Chelated Iron. Adding organic compost to the soil or using compost as mulch can also help to increase acidity and maintain acid soil conditions.





How To Fertilize Blackberry Plants


Blackberry plants will benefit from fertilization, however be careful not to over fertilize them! When blooms start to appear, and again after harvest, you can feed plants with a slow-release shrub & tree type fertilizer. That being said, when feeding plants that will produce food that ends up on the dinner table, I always go the organic route. When using an organic organic plant food, or blood meal, cottonseed meal, or fish emulsion, fertilize in late fall before the first frost. Base the amount of fertilizer applied on the size of the bushes. Follow application rates on product label and be sure to spread the fertilizer evenly under and around the bushes. 




How To Water Blackberry Plants


Blackberry plants prefer a consistently moist, but not a constantly soggy or wet soil. If you have just a few or several plants, hand watering is probably best. When fruits are on the plants, it's best to avoid splashing the foliage and berries with water, which can cause berries to rot. When growing blackberries in long rows, it's more convenient to irrigate with a soaker hose or drip irrigation system.


After Planting 

Immediately after planting deep soak the soil in the planting area, including the rootball, to a depth of at least 6 inches or equal to the height of the root ball. An application of Root Stimulator will provide an extra boost to stimulate early root formation and stronger root development. Root Stimulator reduces transplant shock and promotes greener, more vigorous plants.


During the First Active Growth Season

In average garden soil you should not have to water your new Blackberry plants every day. More often than not, this causes soggy or wet soil conditions that can lead to root rot and other plant diseases. In the absence of sufficient rainfall, water only as needed to keep the rootball and surrounding soil moist. Apply an organic mulch to help retain moisture and reduce hand watering. Keep in mind that deep soaking less frequently is much better than splashing just a little water on the plants every day. Plants planted during the winter dormant season, when plants are not actively growing and evaporation is much slower, will require much less water. So, be careful not to overwater during winter!


Thereafter

When established, Blackberry plants are fairly drought tolerant and will require less water, however will prefer a consistently moist soil when there is fruit on the plant. Lack of sufficient water just prior to and during the harvest season will seriously reduce yields and quality of fruit. This will not only affect the current year"s harvest but also the following year"s crop as the water shortage will limit the production of desirable fruiting canes called "primocanes." Keep plants mulched well to help retain moisture. 






Plant Long & Prosper!

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