Growing Blueberries in Ancient Marl

The blueberry fruit is luscious. I do not know how to describe its taste. It is more its texture and mouth-feel than its taste that gets me. Blueberries are wet-soft through a firm skin, breaking onto squishy ambrosial moisture. The joy of blueberries is that they are gently sweet with a little acidity, moist with a dry waxy skin. Given these subtle fruit beginnings, blueberry jam is thus strangely intense. Alternatively, coating dried blueberries in dark chocolate brings a different intensity—though reversing the firm-soft joy.

There is something about blueberries—small, apparently delicate, vibrant green bushes with round fruit that change from pale green to vibrant blue. Their fresh fruit glistens, dusted with a fine white powder ‘bloom’. Their leaves turn burnt orange in autumn. And then they fall, leaving a tracery of small branches spreading upwards to the light. Teardrop-shaped fruiting buds appear on the last 10 centimetres of the old stems.

Knowing all this, why have I always been unsuccessful with growing blueberries? I have tried to grow them in North Fitzroy a few times. But they have always failed, slowly dying from what I assumed was inconsistent watering or overly heavy, badly draining Merri Creek mud. There we have the same black volcanic vertosol underlay that was used to form the famous MCG sticky wicket, first sourced from the Merri Creek in 1859. Even the new drop-in pitches continue to use Merri Creek clay, alternating with test-soil from the Grampians.

I have always added lots of organic material to the Merri soil. Our city garden is layered in compost from the normal North Fitzroy fare: coffee grounds, vegetable scraps, elm leaves, and charcoal from the ovens of Natural Tucker bakery. This is supplemented by 25 years of composted pizza boxes from La Sera, Joe’s pizza parlour and then Meine Liebe. I was careful to plant in a sheltered position with some sun. I was always semi-attentive to keeping them watered. But it seemed to make no difference. Slowly the plants would wither and die. The simple answer was that I did not know enough about what blueberries actually need. I was bought a soil pH tester for example, and never used it, thinking that Merri Creek black vertosol was naturally acidic.

This Time Will Be Different

This time I plan to research their needs before I plant the bushes. And thus, emerged a plan for a house orchard at Platypus Bend. The orchard will be behind the shed, on a north-facing well-drained slope. It is where the fig has just been planted. I have begun clearing the lanky grass, and beneath the sods the soil is dark grey sandy clay-loam surface soil, overlying, at a spade depth, a mottled yellow-brown, grey silty clay. It does not look as if it has much organic material in it.

The duplex soils are known as the ‘Gellibrand Marl’. This ancient marl has ‘developed where stream dissection has cut deeply into the ancient plateaus, exposing the lower lateritic horizons and tertiary unconsolidated marls and clays’, whatever that means.

What I do know is that Gellibrand is known for its blueberries. Last weekend we attended the Gellibrand Blues and Blue Berry Festival Market at the Rex Norman Reserve. There I met a bloke called Bob from Shoebridge blueberry farm selling young shrubs. I talked to Bob about my plan, and he revealed a resounding flaw with its inception. I was planning to use the old chook run behind the shed because it provided wire-covered protection from the ravaging of hungry parrots, rosellas and galahs. He said, ‘no’. Generations of birds living in that old chook shed would have shifted the pH range of the soil so that it was now too alkaline.

This does not simply mean ‘back to the drawing board’. But it does mean a lot more work on developing the soil before I plant the blueberries. I do not want to kill the new plants this time too.

Growing Blueberries

Plant in spring or late autumn. Be careful not to plant the blueberries too deeply. The root ball should be just below the surface. Plant 1 metre to 1.5 metres apart, depending upon the variety—at the upper end of that figure for larger varieties.

Position

Plant in a sheltered position with all-day sun.

Weather     

Blueberries require 750+ chill hours (hours across a year above freezing but below 7 degrees centigrade). Inner Melbourne, for example commonly gets 700 chill hours.

pH            

Blueberries require 4.5 to 5.5 pH. Soil can be acidified by mixing a small amount of granulated sulphur into the soil several months before planting. Peat moss, coir and pine bark are additions that will acidify the soil. (The acidity of pine needles is a myth.) Given that acidity will leech out, consider what is planted down-hill from the blueberries.

Soil           

Blueberries are shallow-rooted plant that require open soil, rich in organic material, that holds moisture, but also drains well. Gellibrand  is potentially a fabulous place for growing blueberries.

Mulching   

Mulch is essential to keep their shallow root systems moist.

Pruning      

Prune plants in late-winter and early spring before new growth begins. The aim is to create an open vase-shaped bush. For the first few years prune only to remove weak and spindly growth. From then on, pruning is needed to stimulate growth of the new shoots that will bear fruit the following season. Cut out dead, broken, short, weak, and spindly shoots. Begin with large cuts, removing stems that are more than four-to-six years old, stems drooping to the ground, or those crowding the centre of the bush. Remove low-growing branches whose fruit will touch the ground. Select for bright-coloured wood with long (at least 10 cm) laterals. Remove blotchy coloured short growth and small branching sections.

Aim for six to 12 main canes, removing a couple of older canes each year, cutting as close to the ground as possible. There should not be any canes that are more than five-to-six years old. Take out the canes that bear only weak shoots. This allows more sunlight into the bush. New canes will emerge from the ground-level.

Pollination

Blueberries produce better if they are cross-pollinated. This means that growing blueberries of different varieties will help with their production. Bees are essential for a good fruit set, so consider companion-planting to attract bees. The best companion plants for blueberries are basil, thyme and rhubarb. 

Fertilizing  

Fertilize as for azaleas in early spring as leaves are breaking from dormancy. Test the soil, and bring phosphorous up to medium levels. Nitrogen is best absorbed as ammonium ion.

Weeding    

Hand-weed for at least the first year after planting. Hoeing or digging around the bases of plants damages their surface-feeding roots.

Watering  

In the early years, summer watering is necessary for growing blueberries.

Harvesting  

Full sweetness takes a week or so beyond full colour to develop and timing varies between cultivars.