Watering is an important function. Blueberry roots like a moist soil, but they do not like to be overwatered. The roots are shallow and fibrous and are susceptible not only to drought injury but also to root rot. Use a probe to measure the moisture level, or insert a finger into the top inch of soil. If it is dry it is time to water. The greatest water demand is from berry swell through early harvest and when fruit buds are being formed, usually August through mid-September. Two separate irrigations per week should be sufficient, and do provide good drainage to prevent root rot. If they are in containers, check them every other day.
The easiest way to water blueberry plants in a hedge planting would be to lay a soaker hose along each side of the hedge. Each side? Yes, if the roots on one side dry out that side of the top will suffer, blueberries are funny that way. Placing the soaker under the mulch will conserve water and protect your hose. Build a drip system if the shrubs are separated or in containers, placing multiple emitters above each part of the root zone to prevent root sectors from drying out. The most difficult way to water is with a hose, considering it has to be done so often during the dry season and done slowly to give the water time to soak in.
Fertilizing Your Blueberries
Blueberries evolved to use very little food. Lift the mulch carefully because some roots will have grown into it, apply the fertilizer over the root zone and put the mulch back in place. You can scratch the plant food into the surface if it will make you feel better, but use your fingertips and try not to hurt the roots. If your plants require more acidity, this is also a good time to apply a bit of sulfur, but that should really have been added to the planting mix during or better yet, much before planting the thing. Even when sulfur is mixed with the soil, it takes a year or more before the plant and you see pH changes in the root zone.
When to apply fertilizer? Some growers apply half of it in each of two applications several weeks apart. A good time is when the leaves appear in early spring and again when the berries are forming. Don't apply fertilizer to help the plant go into the winter, it is going to want to go to sleep and fertilizer will keep it active. Blueberries will get just as ornery as you do when deprived of sleep.
What type of fertilizer? Blueberries are very much into organics and they thrive with an acidic organic fertilizer such as cottonseed meal, available at any garden center. Ammonium sulfate is also an acidifying fertilizer, but think tablespoons per plant, not cups or pounds. Potassium sulfate is OK. Fertilizer specifically blended for rhododendrons and azaleas is an alternative but check the list of ingredients. Do not use any type of nitrate fertilizer, blueberries do not take up nitrate nitrogen and it becomes detrimental to the plant. Muriate of potash is potassium chloride, also a no-no because blueberries are sensitive to chlorine, don't use anything that ends with -chloride. Do not use aluminum sulfate even though it is acidic, blueberries are not fond of aluminum. Some individuals will use animal manures, but be careful because these may contain too many salts, it all depends on what the animal was fed. Salts and acidity are not the same, salts are chemicals, acidity is a measurement term (like degrees.)
How much fertilizer? We can't tell you because that all depends on the strength of the fertilizer you are using, and that's what those numbers on the package will tell you. Bring your glasses with you so you can read the ingredient list. Follow directions on the container and go easy. The bigger the plant, the larger the root ball and the more fertilizer you can put down, but remember, blueberries don't like fertilizer all that much. A heavy application may make you feel good but it will really stress the plants. Some varieties may like a little extra fertilizer but some don't, so experiment a little, and over the years the plants will let you know what they like best. We use cottonseed meal and each year apply about a cup to younger plants, around two cups to more mature plants.
Blueberry leaves turn red in the fall, and this is normal behavior. But if the leaves constantly have red margins, the shrub likely requires iron or magnesium; you can get advice from a good garden center but be prepared to tell them the soil's pH measurement. Yellow leaves on blueberries can be quickly corrected with a foliar application of 1 tablespoon iron chelate in a gallon of water sprayed over the leaves. You should see greener leaves in a few days. However, the real culprit may be that the soil pH is too high.
Because blueberry roots live near the soil's surface, do not cultivate the shrubs, but cover the soil with mulch to discourage weeds and retain soil moisture. Some of the plant roots will grow into the mulch. The first year apply two inches, the second add to it to create a four-inch-deep mulch, and from the third year on keep the roots covered with six inches of mulch. Use sawdust, wood chips, leaves, whatever is handy, but the best mulch would be pine needles or oak leaves. Why pine needles or oak leaves? They're acidic, break down quickly into an acidic organic material which will keep your soil conditions right. Where does one get pine needles? Look for a brown carpet in the street gutters under trees with cones and long skinny needles, bring a garbage can and something to pick them up with. Ask your Street Department (the street sweeper picks them up) or the Parks Department, they may have a pile of them somewhere. Drive down back roads, look for that brown carpet under trees with cones and long needles. Take a small amount here and there, nature doesn't mind sharing, don't trespass.
Keep that mulch topped up, the right material breaks down quickly, creating carbonic acid—and that is exactly what the blueberry shrubs want. Remember, they thrive in a soil with a very high organic component that is constantly in the process of breaking down, and a deep mulch promotes proper decomposition.
Blueberries fruit on canes that arise from the ground. These are called basal shoots. Pruning promotes new basal shoots. Fruit is borne on the previous year's wood, but production drops off with older canes. The best production is on 3- and 4-year old canes. Pruning is not needed until a blueberry's third or fourth year. You could prune anytime, but winter is probably easiest since you will be able to better see the structure of the plant.
Pruning is simple: Remove all canes that are bigger around than the base of your thumb (or 1½" in diameter). Cut these canes back to the ground or to a strong new side shoot. Next cut off all canes that grow sideways or cross each other. Weak twigs produce tiny berries, so remove them. Cut off dead and broken branches, and any branches that allow fruit to drag on the ground. Open up the inside of the bush to sunlight by removing basal shoots that tend to crowd the inside of the plant or shoots that are smaller than pencil-size in diameter. Leave larger shoots to develop into next year's fruiting wood. Limit the number of canes to one for each year of age of the plant, or a maximum of 6-8 canes for mature bushes. If you remove one or two canes each year, and if one or two new canes are produced, none will be over 4-6 years old.
Flowers (and berries) form at the ends of the canes. Do not shear or shape the shrub because you will cut off the flower buds. However, removing some of the tip to leave only a half-dozen buds will promote the growth of larger but fewer berries.
Blueberry Pests and Diseases
Since a mulch is such an essential ingredient in good blueberry production, weeds are rarely a problem. Backyard plantings are seldom bothered by insects, and there are only a few diseases that cause problems with blueberries.
A grey mold fungus can be a problem during prolonged rainy springs, and Serenade, a strain of bacteria (Bacillus subtilis) can be used to form a protective coating around all parts of the shrub, discouraging the establishment of fungi. This product is available as a concentrate or as a ready-to-use form. Start applying this at flower petal fall and continue as needed. Follow the instructions on the label.
Root rot will occur with blueberries planted in wet areas or in "bathtubs", planting holes that cannot provide sufficient drainage. There is no cure other than moving the plants out of these locations or planting them on mounds.
The biggest blueberry pest is the bird. Protective netting is available at the hardware store. Put a PVC frame over the plant to keep the net off the shrub and use clothespins to keep it closed when you are not picking berries.
NEXT >> Blueberry Types and Cultivars