When it comes to feeding blueberry bushes, your focus should be on reaching and maintaining the low pH soil level the plants love to grow in, rather than gorging them on manure or 10-10-10 fertiliser. Blueberry soil should also boast a loose, light texture high in organic matter, which enables the roots to retain moisture without becoming waterlogged. Careful improvement to the blueberry patch prior to planting should get your bushes off to a great start, while some judicious feeding during the growing season will keep them thriving for years.
Decide on where your blueberry patch will be sited at least a year ahead of planting, if possible. Blueberries love acidic soil, so chances are you'll need to work some acidic material into the ground. Most of these additions need several months to a year to break down before the plants go in.
Test your soil's pH level. Simple soil testing kits can be found at most nurseries and garden centres, or you can send a soil sample to the local extension service. If mountain laurel, rhododendrons or oaks grow near the site, you may already have the ideal acidic levels. 4.5 is the perfect pH level for blueberries, but in general any number between 3.5 to 5.5 should be fine.
If your numbers come back higher than 5.5, you will want to lower the pH level by adding acidic material to the entire blueberry patch, at a depth of four to six inches. Home growers often choose peat moss for this task, but sawdust and rotted leaves can be good choices as well. The National Sustainable Agricultural Information Service recommends adding powdered sulphur to your blueberry patch for lowering soil pH, or lime in the rare cases when the ground is too acidic even for blueberry culture.
Use mulch as another way of feeding your blueberries. While mulch isn't normally a crucial part of the fertilisation process, in the case of acid-loving plants you can feed their low-pH habit by using sawdust, wood chips or pine needles. Mulch thickly to a depth of about six inches.
Purchase fertiliser from a reputable supplier, unless you have your own stock of well-aged compost. Good organic choices to fertilise blueberry shrubs include bone meal, blood meal, cottonseed meal, hoof meal or horn meal. Remember that while you may have needed to add several bushels of soil amendments per blueberry bush in order to adjust your pH level, feeding requires a mere dusting of fertiliser per plant.
When the bushes began to blossom, use the top-dress method to feed your blueberry bushes. To top-dress your plants, simply remove the surrounding mulch, add your chosen fertiliser, water, and replace mulch. The shallow-rooted bushes much prefer this to a tilled-in system, which could damage the plant.
Feed again just before the berries set. Some growers apply a third top-dressing after harvest, but geography and convenience can be factors here. Master gardener Barbara Damrosch notes that for Northern growers, post-June feedings can actually be too late in the season and could interfere with the dormancy period.
Blueberry bushes can also be fertilised through foliar feeding, which utilises liquid fertiliser sprayed directly on the plants' leaves. Good choices for liquid fertilisers include fish and seaweed emulsion, applied as the buds begin to form, just before harvest, and, for southern growers, post-harvest. If using chemical fertiliser, go for bags marked "for acid-loving plants." Plant food designed for azaleas and rhododendrons should work well on blueberries.