While reading articles about planting both Raspberries and Blackberries, I have several times now seen a sentence that states that you should not plant these close together, but there is no reason given as to why you should not plant them close together.

Anyone know why you should not plant these 2 close together?

I have a 20' x 3' planting of blackberries on one side of a solid fence and a 15' x 3' planting of raspberries on the other side of the fence. I have had these there for about 3 years and they seem to be doing fine.

Answer #1 · Maple Tree's Answer · Hi Troy-Very interesting question. Not having much practical experience growing these berries I immediately thought of their growth characteristics. The raspberry normally being a smaller somewhat bushier plant than the blackberry's larger more spreading, rangy, more invassive, characteristic. They both require pruning to allow sun light and air circulation for healthy growth. The over powering or over shadowing of the blackberry may affect the raspberry's growth and fruit producing. The different needs of these plants regarding pruning and fertilization times of the year would also add to the difficulty of treating the plants individually when planted close together. The raspberry able to withstand somewhat cooler weather than the blackberry may be another reason that may affect ones health over the other also.
I found that the raspberrys can carry a latent virus that may not show or affect themselves, but can be trasferred by aphids to the blackberry that is not as resistant to disease. Many articles recommend planting the raspberry at least 600 feet from other berry plants. These are a few reasons I believe articles you have read feel it unwise to plant these berries close to one another. The fact that your plants are separated by a solid fence i'm sure has added to the success you have had for three years. I Hope this sheds some light on your question. Possibly others that may have some practical experience regarding your question will come up with other reasons not to plant these berries close together.)