I have possibly hundreds of volunteer raspberries shrubs, but they don't produce that much. What should I do (in the way that is most cost and time effective) to make them productive? Cut them down so they get a fresh start? Fertilize them? Thin them out to give them less competition (how?)?
Are wild raspberries just that much less productive than commerical varieties?
In my very limited experience, the black raspberries that grow on poor soil don’t produce many berries, and they are tiny. I had wild black raspberries grow on my garden made of tons of leaves, which became magnificent soil, and they produced slightly bigger, and certainly more, berries.
I'm far from expert but was just reading up a bit about this because I have an inherited raspberry in a big pot that I've been trying to restore to productivity. In a pruning book I have they recommended cutting back every cane that fruits after the fruit is harvested to maximize yield. They claim that raspberries fruit and second year canes and older but that older canes produce progressively less fruit but still occupy pretty much the same amount of the plants energy. My poot orphan is currently failing to set fruit well after a promising season of flowers so I am planning to just cut out every cane that tried to fruit and see if this years new growth does better next year.
You might try cutting back a bunch of the old canes and see what happens
I don't know how the wild raspberries grow but I would think cutting the old canes back in the fall would make sense--at least that helps my cultivar raspberries. You could also try spreading mulch such as fall leaves around them. That could help them have more moisture for berry production.
Cultivate abundance for people, plants and animals - Wild Homesteading
I find that raspberries left to sprawl will focus their effort on sprawling instead of producing fruit. It's as if they need the stress of being forced to grow in a defined area, with suckers ruthlessly chopped off or tilled, to focus their efforts.
Wild or feral raspberries sprawling through the undergrowth only seem produce in a very wet year, and even then it's hardly a snack.
There is definitely a difference between cultivars. We have a hardy, spiny, vigorous and flavourful variety that we bought or were gifted more than 20 years ago. They were from a garden shop but unfortunately I've forgotton the name of the variety. In addition to our own garden, shoots from these have been given to at least a dozen other people, replacing the canes they had before.
Different ecosystems may require different management. I live on the Pacific Wet Coast, and the raspberries here definitely grow taller and some years produce two crops unlike Southern Ontario where I grew up, so how I manage mine now should be taken with the proverbial grain of salt.
1. When they're blooming, I normally see tons of bees on them. If you're seeing lots of flowers but not much fruit, try hand pollinating a few plants to see if it makes a difference. (mark the plants in some way so you know which ones you pollinated) If you aren't seeing many pollinators, you may have to plant other things in other parts of the year to support your localbees.
2. I contain mine in rows between wires tying them on when necessary to keep them upright and maintain airflow. This decreases the tendency for them to go moldy which may well be less of an issue where you are. I make sure the wires "hook" on so they can be easily unhooked to prune out the old canes.
3. I use a *lot* of wood chip mulch on the paths and between the plants. Raspberries seem to really like woody mulch.
4. Mine normally produce in July (after strawberry season). I don't water them while they're producing, so once they've produced, the productive canes tend to die back. Thus, I'm actually aiming to prune out the old canes from the bottom in August or Sept depending on weather and time available. After pruning, if we're getting our usual summer drought, I water them *really* thoroughly and deeply, and then apply fresh woody mulch +/- chop and drop weeds. Again, I find it really helps to wood-chip mulch the paths on either side of the narrow raspberry beds.
5. The new canes that came up in the spring will often start blooming in Sept. This will not stop them from producing the following year, but any fruit they form is usually not very sweet due to the cooler, less sunny conditions. That said, the bees benefit from the pollen and bees and wasps will be seen drinking the juice from the fruit, so I may pick some of them, but I also leave some to support the insects.
So, yes, if it were me, I would at least try to resurrect the berries. Yes, they may have reverted to wild and you may decide to replace them, but if you mulch them well and observe carefully what is happening, you may find some plants that are still good. I do find that older varieties tend to form smaller fruit, but it tends to be more flavorful rather than more "sweet". I've been propagating both my raspberries and strawberries for 25 years now and many people whine that they're "small" but then rave at how good they taste. You may have to identify and choose the best plants out of the rambling mess, but it may be worth it.
I was asked to expand on my comment about supporting raspberries:
I've used a number of systems, but the basic principle I try to follow is to have the wires (usually recycled clothesline wire) easy to remove and replace. This way when I need to prune, I can simply unhook the wire loop. In this case, a piece of board is held to a T-bar with some U-bolts and some cup-hooks hold the wire loop. There is a second one about 18 inches off the ground and the one pictured is about 4 ft, but some of the raspberries I've been growing are easily 6 ft tall. My neighbor prefers to cut his so that they are shorter, but my limiting factor is sunlight, so the taller they are, the better sun they get.
This particular set-up used metal clips that you bend onto the wire. When I can get them, I prefer "wire rope clips" which are miniature shaped u-bolts that are tightened with nuts and can be removed. I tend to move my raspberries around the garden every 5-7 years, so it's good to be able to change the system as things develop.