Blueberry Growing Calendar: What to Do Season by Season

The shape of the blueberry year

Blueberries run on a long cycle in which the work and the reward are separated by months. Flower buds form in late summer for a crop the following summer. Chill accumulates through winter to make those buds open evenly. Pruning in late winter decides how many of them there are. Nothing you do during picking changes this year's fruit much, and almost everything you do after picking changes next year's.

Most disappointing crops trace to a job done in the wrong season: feeding late in the year so growth is soft going into winter, pruning in autumn, or letting the bush go dry in the weeks right after picking when the buds are forming.

Match the type to your winters and summers

Everything in this calendar assumes the plant is suited to your climate, and that comes down to chill. Through winter the flower buds accumulate hours below about 45F (7C), and until they have had enough of them they will not break evenly in spring. A bush short of its chill requirement leafs out raggedly, flowers over a long straggling period and sets a fraction of the fruit it should.

Northern highbush types want a lot of chill, typically 800 to 1,000 hours, and tolerate hard winters in exchange, but they suffer once summers run above 90F (32C). Rabbiteye and southern highbush need far less chill, often 300 to 600 hours, and carry heat that would cook a northern plant. Choosing against your climate is the commonest reason a healthy-looking bush never crops well, and no amount of feeding or pruning corrects it.

Rabbiteye also ripens later and over a longer stretch than highbush, and grows far larger. A mixed planting of both, where your climate suits both, stretches the picking season by several weeks.

Late winter and spring: prune, feed, protect the flowers

Pruning comes first, while the bush is bare and you can see the structure. Take out the dead wood, then one or two of the oldest gray canes at the base, then anything low or crossing. This is also the moment to test the pH, because sulfur applied now has months to act before it matters.

Feed as the buds begin to swell, using a fertilizer formulated for acid-loving plants so the nitrogen arrives as ammonium. Spread it over the root area out to the edge of the canopy and water it in. Then leave the plant alone through flowering: do not spray, and cover only on nights when frost is actually forecast.

1. Prune before the buds swell Late winter, once the hardest cold has gone. Fat rounded buds are flower buds and small pointed ones are leaf buds, so you can see exactly what each cut costs you.
2. Feed at bud swell, not before A dormant plant cannot take up fertilizer and it simply washes away. Wait until the buds are visibly moving, then apply once, and a second lighter dose after picking.
3. Top up the mulch Add an inch or two of pine bark or needles to bring the layer back to three inches (8 cm). It has broken down over the winter, and the shallow roots need it before the dry weather arrives.
4. Row cover only on frost nights Open flowers are killed by a late frost and the blackened centers never set fruit. Cover on the forecast nights and uncover in the morning so pollinators can work.

Do not spray anything, even organic products, while the flowers are open. Blueberries depend on bumblebees for a heavy set and there is no cheaper way to lose a crop.

The critical weeks: fruit swelling and picking

From petal fall until the berries color, water is the limiting factor. This is when berry size is decided, and a dry fortnight here means small fruit no matter what you do afterwards. Aim for one and a half to two inches (38 to 50 mm) of water a week, delivered slowly at the base.

Net before the first berry shows color, not after you notice the birds. Then pick every three or four days through the season, waiting until each berry has lost the pink ring at its stem and had a few days beyond that. Take off anything over-ripe or shriveled at every pass so rot does not spread.

After picking is when next year is made

The weeks after the last berry are the ones most gardeners waste. Flower buds for next year form on the current season's shoots during late summer, and the plant needs steady moisture and a little nitrogen to build them. Stopping the watering the day picking finishes is directly responsible for a great many light crops the following year.

Feed lightly once after picking, keep watering through late summer, and then stop feeding by early autumn so the new wood hardens before the cold. Taper the watering in late autumn as the leaves color and drop, and leave the bush alone through winter, when it is doing the invisible work of counting chill hours.

Autumn color on a blueberry is spectacular and it is a sign of a healthy plant shutting down properly, not of a problem. A bush still carrying soft green growth at leaf fall was fed too late.

Working out what went wrong

When a season disappoints, the cause usually sits several months earlier than the symptom. Small berries point back to watering during fruit swelling. Few flowers point back to the previous late summer or to over-pruning. Yellow leaves point back to soil pH regardless of what you fed.

Four dates a year are enough to make this diagnosable: the day you pruned, the day the first flower opened, the day of the first ripe berry, and the day of the last picking. Kept for two or three seasons alongside a note of the soil pH, those dates turn a vague sense that the crop was poor into a specific, fixable cause.