Biting into a sweet, vine-ripened blackberry is a highlight of spring. When allowed to ripen in the garden under sunny skies, blackberries are sweet, juicy, and highly flavorful. If the blackberries you grow aren't sweet and are instead bitter, that can be disappointing. There are several reasons blackberry bushes may produce bitter blackberries, and there are solutions for ensuring your plants grow sweet fruit.
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If the blackberries in your garden are bitter, you are probably picking them too early. Blackberries need to ripen on the vine. Other common reasons for sour blackberries include improper soil pH, not enough fertilizing, and incorrect watering.
Harvesting Too Early
Unlike some fruits that ripen after you pick them, blackberries must ripen on the vine. If you harvest the berries too early, you will have sour blackberries. While on the vine, the blackberries will ripen over a span of several weeks. If you picked the berries when they were bitter, they will remain that way.
To harvest blackberries in the spring that are sweet and tasty, wait until the berry is plump and still firm but has become a deep black, dull color and is no longer shiny. Ripening occurs after the blackberries become black. The berry should easily come off the vine when you are picking it. If you must yank at the berry to get it off the vine, it isn't yet ripe enough for consumption and will likely taste bitter. For maximum sweetness, harvest blackberries every four to seven days.
Preserve the sweetness in blackberries by harvesting during cooler times of the day, such as in the morning. Place blackberries in a shallow container as you pick and keep them out of direct sunlight. Refrigerate them as soon as possible after harvesting, which will preserve the sugar content of the berries. Don't wash the fruit until you are ready to eat the berries. Blackberries are highly perishable, so eat them within four to five days after harvest.
Improper Soil pH
To grow healthy blackberry vines, the soil pH must be at a specific range. Soil pH refers to a range of alkaline and acidic conditions that affect the absorption of nutrients in the soil.
For successful blackberry growth, you need a soil pH between 5.5 and 6.5. This is considered acidic. If you are going to plant blackberries and want to ensure they are sweet or if you are having difficulty growing sweet blackberries, perform a soil test to determine the pH of the soil. If the soil test shows that conditions are too alkaline for blackberry plants (higher than 6.5), you will need to amend with soil sulfur, aluminum sulfate, or chelated iron. If your soil is too acidic (below 5.5), you will need to amend with garden lime.
Inadequate Fertilizing During Production
Blackberry plants require nutrients to grow well, bloom, and produce tasty fruit. Fertilize in spring when the vines bud up and again after harvest with an organic fruit tree fertilizer. You want to feed all blackberry varieties the same way by following package directions when applying the fertilizer.
Incorrectly Watering Berries
Blackberry soil needs to remain moist for good fruit production. It is important that the roots don't dry out. Each time you water, make sure that the soil is wet to a depth of 6 inches to 1 foot. Check the planting area with a soil moisture meter to ensure that the soil is sufficiently wet. Sandy soil is much more porous and will require more frequent watering than heavier soils, like clay. Soak the soil slowly with a hose or use a soaker hose or drip irrigation.
What to Do With Bitter Berries
If you harvest bitter blackberries, it's still possible to enjoy them. You can soak them in a sweetener and liquid. Good sweeteners for soaking blackberries include honey, maple syrup, and table sugar. Along with the sweetener, add some fresh juice or sweet liqueur. Mix 1/2 cup of sweetener with 1/4 cup of liquid and steep the blackberries for one hour at room temperature. Then, use the berries or refrigerate them. Blackberries can also be used to make jam, smoothies, and pies.
- Oregon State University Extension Service: Growing Blackberries in Your Home Garden
- Almanac: Blackberries
- LSU College of Agriculture: Blackberry Growing Guide
- Wilson Bros Gardens: How to Fertilize and Water Blackberry Bushes
- Suny College of Environmental Science and Forestry: Soil pH: What It Means
- Bon Appetit: How to Fix That Carton of Sour, Sad Berries You Impulse-Bought