This has ~ 300 grass plants, which seems to be about my limit before Blender crashes (5 samples).
Maybe cpu render helps
My scene has > 5000 plants) and its ok with cpu
I’ll give that a try - though my cpu is so much slower than the gpu.
Between my three particle systems I’ve got 56,250 grass objects in the scene 
Two of the three systems have 500 hairs (one with 50 children and one with 75) while the third only has 250 (also with 25 children). Having to switch to CPU wasn’t that much of a hardship, just remember to keep your samples low <10 and limit what you are rendering for your prototypes.
While my final render (1920 x1080 @ 100% with 1000 samples took 11 hours to render), none of my prototyping took more than a couple minutes. The secret is in managing what your are actually rendering!
Here is a look at what I did with the CPU. This has ONLY the short grass blade (no plants). The GPU chokes on this (I actually cannot tell as there is no error). There are many many objects (at least 10,000 before I started adding a lot more with the particle editor, mostly on the hills). It took about 3 times as long as the GPU so not too bad.
Sometimes less is more.
Heres my Bunny in the particle grass. And it took also 6-7 Hours to render. Whew! will try and reduce the memory\triangles used. to bring the render time used!
