How Big is a Blueberry? A Look at Blueberry Sizes

Plant Growth Cycle & Yields

Two-year-old bare-root nursery plants 1 to 3 feet tall are transplanted in late winter or early spring. Potted plants can be transplanted in the fall. Growth begins with bud swell in the spring and continues into late summer and fall. The blueberry produces several flushes of rapid shoot growth. Each growth flush ceases when the uppermost or apical bud aborts (this is not a disease). Soon after, a bud “breaks” near the tip to begin another flush of shoot growth. During the growing season, each shoot may go through several of these growth flushes. If the shoots get enough water and food, each flush can lead to 6 to 10 inches of growth. Shoot growth usually stops in midsummer.

Typically, five to eight flower buds can develop on a healthy shoot. Each flower bud can hold five to ten flowers, which continue to grow inside the bud all through fall and early winter. Both vegetative and flower buds become dormant in winter. In the spring, flower buds open one after the other, starting with the buds at the very end of the cane. Each flower inside a bud opens in a similar order, with the flower closest to the tip opening first. Shoot thickness affects blooming sequence, with blossoms on thinner wood opening up earlier than buds on thicker wood.

In the first and second years after planting, it’s best to cut off all the flower buds to help the shoots and roots grow well. Blueberry flowers and fruits use up a lot of energy for the plant. If the plant doesn’t grow well in its first two years, fruit yields may be lower in later years. It is important to cut off the flower buds and the top third to half of all shoot growth on rabbiteyes before transplanting them.

Blueberry fruit ripens over a two-month period after bloom. This will vary with the cultivar, weather conditions and plant vigor. In their third year, plants should yield about half a pound per bush. In their fourth year, they should yield between 1 and 2 pounds per bush. With good care, mature Southern highbush plants can produce more than 8 pounds of fruit each year. Rabbiteye can produce 12 to 25 pounds.

To change the pH of the soil, get a test done in the fall before you plant in late winter or early spring. If the pH is above 6. 0, select another planting site. If the soil pH is below 6. 0 but above the 5. 5 limit, apply wettable sulfur (90 percent sulfur). A very low soil pH caused by excess sulfur can be detrimental. Some soils in the Piedmont are very high in manganese. When growing blueberries on these soils, keep the pH above 5. 0 to avoid problems with manganese toxicity. Putting down sulfur should happen at least three months before planting, since it takes a while for sulfur to lower the pH. Once or twice during the first growing season, check the pH to see if more sulfur is needed later in the season.

Sometimes, the impatient home gardener will insist on planting without a soil test. In this case, mix 1 cubic foot of peat moss with an equal amount of sand. It is important to use sand that has not been limed or does not have any lime in it. Most builder’s sand, referred to as “sharp” sand, does not contain liming materials.

Soil Water Drainage: If you have heavy clay soil or soil that stays wet sometimes, mix peat and sand together and spread it on top of the soil. Then plant your seeds. If the soil drains well, you can put some of the peat-sand mix in a hole or furrow that is a few inches below the surface. Just make sure you leave at least 6 inches of the peat-sand mixture above the soil surface. This will help you make a mound for a single plant or a ridge for a row of plants. The mound or ridge will keep the plants from getting too much water, but it’s still important to water deeply two or three times a week during dry times in the summer and early fall when you plant this way. The soil mix in the raised bed can be held in place with rocks, bricks, concrete blocks, landscape timbers, or logs.

Organic matter additions before planting: Blueberries naturally grow best in soils with 3 percent or more organic matter, while most mineral soils have less than 1 percent organic matter. Before planting, add organic materials like peat moss, composted pine bark, or rotted softwood sawdust to soils that have less than 2 percent organic matter. This will help blueberry plants live and grow much better. Hardwood sawdust is not as effective as softwood sawdust or peat moss for lowering soil pH. Undecomposed softwood sawdust should not be used.

Follow this popular step-by-step pre-plant program to modify soils with less than 2 percent organic matter:

• Make the plant mounds or ridges (3 feet wide) to help the soil drain better in areas that don’t drain well;
• Spread 4 to 6 inches of organic matter across the row in a band 18 to 24 inches wide. Use a rototiller or spade to work the organic matter into the soil to a depth of 6 to 8 inches.

Steps 1 and 2 should be done in the fall before planting in late February or early March, depending on where you live. It is possible to add sulfur to lower the pH at the same time as the organic matter if it is added in the fall.

Note: It’s hard to control the amount of water and nutrients in pure organic matter, so plants are more likely to struggle and die.

Plants: Two- or 3-year-old nursery plants 1 to 3 feet tall will transplant well. Keep the roots moist at all times between digging and replanting.

Time: Bare-root plants do best when planted in late winter, as soon as the soil can be worked (February–March). Potted plants have also done well when planted in the fall (November–December) on sandy soils and in other places.

Spacing: Southern highbush – 4 to 5 feet in the row and 8 to 10 feet between rows. Rabbiteye – 6 feet in the row and 10 to 12 feet between rows.

Depth: Plant to the same depth that the plants were growing in the nursery or the container. Lightly firm the soil around the plant with your feet and water thoroughly.

Cut Back: Remove all shoot tips that have flower buds (plump rounded buds). Avoid making cuts near the base of the plants that will provide an entryway for stem blight disease. To help plants stay alive and grow, cut off two-thirds of the top growth on bare-root plants and half of the top growth on potted plants. Leave only one to three of the most vigorous upright shoots and any other growth near soil level.

Surface Mulch: Putting a 2- to 3-inch layer of organic material like bark, wood chips, sawdust, or pine straw on top of the soil after planting makes the soil more evenly moist, keeps the soil at a comfortable temperature, and helps plants grow and survive in general. Pine bark chips or sawdust have a pH between 3. 5 to 4. 5 and are more desirable than the same mulches from hardwoods with a pH above 5. 0. However, surface-applied hardwood mulches have been satisfactory. Avoid sticky hardwood sawdust that will “seal” the bed and prevent water infiltration.

Use Caution: Blueberries are easily damaged by excess fertilizer. Apply the recommended amount and allow 4 inches of rain or an equivalent amount of irrigation between applications.

First Year: Do not fertilize immediately after planting. Once the first leaves are fully grown, put one tablespoon of a special azalea fertilizer (12 inches around each plant) in a circle that is 10-5-4, 10-8-8, or 11-7-7. Do this every six weeks or so, depending on whether it rains or you water, until mid-August in the Sandhills and Coastal Plain and mid-July in the Piedmont. If a soil test shows that there is a lot of phosphorus, use a half-tablespoon of ammonium sulfate instead of a full fertilizer for the second and subsequent applications.

Second Year: Double the first year’s rates, but increase the circle around the plants to 18 inches. Make the first application when new growth begins in the spring.

Plants That Bear Fruit: When the plants start to grow in the spring, spread 1 cup of a complete fertilizer, like Azalea fertilizer, 3 feet around each one. For stronger growth, add a quarter-cup of ammonium sulfate every six weeks as a sidedress. However, don’t fertilize after July 1. On mature bushes, 6 to 12 inches of new growth is adequate. To keep the plants from getting too big and losing their ability to produce, any extra growth must be cut back. Judge the sidedressing requirement on the amount of shoot growth and leaf color.

Lowering pH: If a soil test shows that the pH level is a little too high in an established planting, add ammonium sulfate as a sidedress and iron sulfate as needed to stop the leaves from turning yellow.

Weed problems should be rare if mulch is put down after planting and replaced every year at a rate of 1 inch. Pine straw is acidic and makes an excellent mulch. Handpull or hoe the occasional weed growth. Avoid deep cultivation since blueberry roots are very near the surface. Hoe no more than about 1 inch deep.

Since blueberries grow from buds on wood that is one year old, pruning should be done in a way that encourages strong new growth every year. Rabbiteye blueberries usually don’t need as much pruning as southern highbush blueberries because they are strong and can support and grow heavy crops of big fruit. During the first five years little pruning will be required. Remove lower twiggy growth, dead or damaged shoots, and weak, spindly growth. Tip back excessively long and limber shoots to stimulate lateral branching and to thicken the shoots. Prune young plants during the dormant season and immediately after harvest with older plants.

If the plants get too tall to easily harvest, cut off about a third of the older canes during the winter. When rabbiteyes are pruned each year, up to seven canes are usually left. Starting in the fifth year, the oldest or biggest cane is cut off each winter. These precise cuts should be made to open up the plant’s center so that more light can reach it and new canes can grow to replace the old ones.

Southern highbush blueberries require annual pruning to prevent overbearing and to maintain vigor. Prune during the dormant season; late winter is most desirable, especially in the mountains.

If the flower buds were taken off after planting, only the flower buds and any weak, damaged, or diseased growth will need to be pruned the next year. Leave some flower buds on strong shoots after two growing seasons to get a small crop the third year. To prune plants that are ready to bear fruit, cut off low-spreading branches and branches that grow through the middle of the bush. Especially cut off weak or old branches. Cut back extremely vigorous 1-year-old shoots and remove most small slender branches. If getting things done early is important, keep in mind that the berries that grow on small, thin laterals are usually the first to ripen. This should be taken into account when deciding how many of these shoots to cut off. Extra long side shoots that bear fruit must also be tipped back until only four to six flower buds are left.

Highbush blueberry plants generally reach their peak production between 8 and 10 years of age. To maintain bush vigor with the continued production of high-quality fruit, renewal pruning must be practiced. Begin the renewal process when the bushes are about 6 years old. First, remove any weak or diseased canes entirely. Starting with the oldest canes, cut back about two each year until they reach strong side branches or are only one foot above the ground. New strong lateral branches will usually develop below the cut. Through renewal pruning, a new upright framework can be developed over a four- to five-year period.

Blueberries may be troubled by fungal leaf spots, fruit rots, root rot and gray mold. The main pests are the cranberry fruitworm (its silk ties the berry clusters together), the Oberea stem borer (its larva bores down the stem, killing it), Japanese beetles, and yellownecked caterpillars. The latter two insect pests feed on blueberry foliage.

Bird Protection: Birds also harvest blueberries, often the complete crop from a small planting. Plastic or cloth netting draped over the bushes or supported on a framework is the only practical control.

Frequency: Southern highbush blueberries have the best quality when picked every five to seven days depending on temperature. Rabbiteye tastes better when picked less often, about once every 10 days. This lets the flavor reach its peak with few soft, overripe fruit.

Important stages in the growth of blueberries’ fruit and leaves are (A) the dormant stage, which starts when the leaves fall off and shows one flower bud; (B) the blooming stage, which shows the group of flowers and the plant stem that grew from the two dormant buds; (C) the fruit set stage, when pollinated flowers start to turn into small fruits; and (D) the fruit development stage, which lasts from fruit set to fully grown fruit. When the fruit is ripe, it’s often easy to spot both flower buds and vegetative buds for the next season on the shoots.

Document last updated on 03/23 by Millie Davenport.

If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.

Robert F. Polomski, PhD, Associate Extension Specialist—Environmental Horticulture/Arboriculture, Clemson UniversityGreg Reighard, PhD, Extension Fruit Specialist, Clemson University

Joey Williamson, PhD, HGIC Horticulture Extension Agent, Clemson University

This information is given with the understanding that it is not meant to be biased. The Clemson University Cooperative Extension Service does not endorse any brand names or registered trademarks, and products or manufacturers that are not named are not meant to be biased either. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All pesticide use suggestions are only for South Carolina and were legal at the time of publication. However, state and federal regulatory agencies can change the status of registration and use patterns at any time. Follow all directions, precautions and restrictions that are listed.

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