Boysenberry

Any time from midwinter until buds begin to swell - January in mild zones, March where winter runs long - pick the best three to eight canes that came through winter and cut the rest out at the ground, along with anything dead, damaged, or diseased. Loop the keepers around the trellis wires and shorten their lateral branches to 12 to 18 inches. Haul the cuttings out of the planting. Only these canes will fruit this year, and the plant ripens what it can feed. Fewer canes with shortened laterals means bigger berries, easier picking, and air moving through the row instead of a damp tangle. Prune before bud swell so the cuts are made while the plant is still dormant.

On an established row, spread 3 to 5 pounds of urea (45-0-0) or ammonium sulfate (21-0-0) per 100 feet of row as growth begins, and water or time it to rain so it moves into the root zone. The new canes that grow this year are next year's whole crop, and they build that growth on early-season nitrogen while the shallow roots are active.

Gray mold is difficult to prevent with fungicides, so the canopy does most of the work: keep the row pruned and open, avoid crowding, do not push nitrogen, and keep weeds down so flowers dry fast. If wet weather is forecast while flowers are open, a protectant fungicide can be applied ahead of the moisture. Bacillus subtilis, copper, horticultural oil, neem oil, chlorothalonil, and thiophanate methyl are listed as potentially effective. If wet conditions persist, more than one application may be warranted. Botrytis overwinters as sclerotia on infected canes and infects flowers only once they open. The infection then sits dormant inside the berry and collapses it into gray fuzz as it nears ripeness, so a spray after you see rot is already too late.

Once the soil has warmed, give the planting 1 to 2 inches of water per week, more in heat, and keep it steady rather than letting the row dry out and then flooding it. Boysenberry roots are shallow and dry out fast. Water stress shows up as weak new canes, poor fruit set, and small, seedy berries, and by the time you see it the crop is already reduced.

Once fruit has colored and started to sweeten, treat for spotted wing drosophila. Spinosad is the main organic option and pyrethrins can go on closest to picking. Rotate by mode-of-action Group number rather than just by product name, and do not use the same Group more than twice in a season. Unlike ordinary fruit flies, spotted wing drosophila has a saw-edged ovipositor and cuts into sound, ripening fruit on the cane. The maggots are inside before the berry looks wrong, and sprays only kill adults, so the window is before egg laying.

Pick when the berry has gone dull rather than glossy and slips off the cane with no tug. Go through the row every 2 to 3 days, harvest in the cool of the morning, and get the fruit down to 35 to 40F right away - it holds about a week. Boysenberries are soft and go over quickly, and warm fruit breaks down in hours. Picking often also strips out the overripe berries that spotted wing drosophila breeds in, so frequent harvest is pest control as much as it is a crop.

When the last berries are off, cut every cane that fruited down to ground level and haul it out of the row. Pull off any mummified berries and dead leaves clinging to the canopy while you are in there. A floricane fruits once and then dies, and it dies carrying the Botrytis sclerotia and cane disease that will infect next spring's flowers. Removing it opens the row up for this year's new canes and takes the inoculum out with it.

Do not lift this year's new canes onto the trellis in fall. Coil them on the ground along the row, cover them with straw or loose mulch, and leave them there until late winter. Do not tip or shorten them going into winter. Boysenberry is a trailing blackberry with tender canes, and the tips die back first. Canes left low are insulated by snow and mulch instead of standing exposed to wind and cold, so more live wood survives to fruit.