Blackberries are a delicious gourmet treat that may be eaten fresh or used in cobbler, cake, sauce, jam, jelly or syrup. Unfortunately, many blackberry cultivars (varieties) do not perform well in Iowa. However, if the right cultivar (variety) is chosen, blackberries can be grown in the home garden.
Growth and Fruiting Characteristics
To successfully grow blackberries in Iowa, it is important to understand their growth and fruiting characteristics. Blackberries are perennial plants with biennial canes or shoots. The shoots of blackberries are strictly vegetative during the first growing season. These first year canes are referred to as primocanes. The following year, these same canes, now called floricanes, produce fruit and then die. Blackberries produce new canes from buds located on their crowns. Some also produce root suckers.
Blackberries are classified according to their growth habit. They can be erect, semi-erect, or trailing. The erect type has upright, thorny canes that do not require support. They are more winter-hardy than the other types and have large, usually sweet berries. Semi-erect blackberries include cultivars that are thornless and thorny; they produce higher yields than the erect type. The semi-erect types do require some support, but their fruit is large and can range from tart to sweet. Trailing blackberries are the least winter hardy and also can have thorns or be thornless. They require a support and have large berries with excellent, sweet flavor.
Blackberries are not widely grown in Iowa because the canes are often severely damaged or destroyed in winter. As a result of this damage, blackberries often produce few if any fruit on those portions of the canes above the snow line. The hardiest blackberry varieties for Iowa are 'Darrow' and 'Illini Hardy.' 'Darrow' has large, sweet fruit and a long harvest season. The canes are vigorous, erect, and thorny. 'Illini Hardy' produces medium-sized fruit on vigorous, erect, very thorny canes. It is also Phytopthora resistant.
There are also two new selections available to home gardeners; 'Prime-Jim' and 'Prime-Jan'; both erect, thorny types. These were introduced by the University of Arkansas and are the first available cultivars of primocane-fruiting blackberry. They will fruit on current season (primocanes) and second season canes (floricanes). Home gardeners should try these new cultivars on a limited scale to determine their adaptability to their climate zone.
Blackberries grow best in well-drained soils with a pH of 6.0 to 6.7. Heavy clay soils can often be improved by incorporating compost or well-rotted manure into the soil. Avoid low-lying areas and make sure the plants are in full sun. Well-drained soils are essential as plants are susceptible to several diseases in poorly drained soils.
Bare-root plants are best planted in early spring. Container-grown plants may be planted any time between early spring and late summer. Both bare-root and container-grown plants should be set 3 feet apart within the row. When planting bare-root blackberry plants, dig a hole slightly larger than the spread of the plant's root system and set the plant 1 to 2 inches deeper than it was grown at the nursery. Backfill with soil and cut the canes down to within 2 to 4 inches of the soil. Water the plants thoroughly. If you are planting more than one row, allow 4 to 6 feet between the rows.
To maintain plants, be sure to water in dry weather and use mulch to conserve soil moisture and control weeds. Pruning on a regular schedule is also beneficial to the growth and health of the plant.
Pruning Erect Blackberry Varieties
In late winter or early spring, prune out dormant floricanes that are diseased, damaged or crowded, leaving four to six healthy canes per plant. Side branches also need to be pruned to a length of 12 to 15 inches to encourage larger fruit. When new primocanes reach a height of 30 to 36 inches, pinch off tips of the new canes to encourage side branch growth and development. Immediately after harvest, the floricanes of erect blackberry varieties should be cut down to the ground. Remove the pruned material from the garden and destroy it.
Insects and Diseases
There are a few insects and diseases that can attack blackberries. Knowing what to look for is the first step in controlling any problems.
Anthracnose may cause small purplish spots on young canes and spurs. These spots enlarge and become oval in shape and sunken. They have gray centers with raised borders. If the planting is seriously infected, anthracnose is best controlled by removing and destroying all canes during the spring pruning. Use of a fungicide labeled for blackberries is suggested every two weeks when the flower buds begin to open until the end of flowering.
Verticillium wilt causes the leaves to turn yellow, starting at the bottom of the canes and progressing upward. Infected canes are stunted and eventually wither and die.
Phytopthora root rot is recognized by dark, water-soaked areas of discoloration at the base of the cane. The leaves will yellow and eventually die.
The fungi that cause phytopthora root rot and verticillium wilt live in the soil and occur under wet and poorly drained soil conditions; therefore, good drainage is crucial. Dig up diseased plants, including roots, and destroy them.
Orange rust is also a concern on blackberries. In the spring, the undersides of the leaves are covered with bright orange fungal growth. Diseased plants will have to be dug up and destroyed.
Sap beetles may damage ripening fruit. For best control, pick all ripe berries promptly. Trap beetles by putting out over-ripe muskmelon. Place traps near, but not in the planting.
Cane borers, such as the long-horned beetle larvae, sometimes tunnel inside stems. Adults are dark colored beetles with yellow or orange markings. In June, the female beetle makes two puncture wounds on the cane, girdling the stem near the tip. Prune the wilted tips back a few inches below the girdle and destroy the pruned material.
The best time to harvest is in the morning, during cooler temperatures, but after the dew has dried. The berries are ripe when the fruit is fully colored and they come off the plant easily. After the berries are picked, they should be refrigerated immediately since they can only be stored for three to four days in the refrigerator. Another option is to freeze the fruit and use them at a later date.
With a little effort and the right cultivar, you could be enjoying blackberries for years to come. I should caution, however, that blackberries are very addictive and everyone in the neighborhood will be asking for a sample!