I grow malabar spinach every year, and it THRIVES in heat waves. It's the only thing in my garden that doesn't wilt when the temperature is 107F, and I have it covering a six-foot trellis. In past years, the plant used to develop perforations in the leaves later in the summer, and it was suggested to me that it might be fungus. These days I spray with Daconil and never have that problem.

Sounds like your problem is root damage, either from animals or maybe root rot? I've never seen that. The quickest way to get new plants is with cuttings. The hard seed coat takes months to degrade to the point that a seed (at least, an unscarified one) can germinate.

This page seems to suggest that root rot can be a problem.

https://www.smartgardener.com/plants/6521-spinach-red-malabar-spinach/diseases/789-root-rot

Don't overwater. Even in torrid heat, my plants seem to need water rarely. I water when they droop a bit, which is infrequently.

thanks for your reply! yep, I bet root rot was the problem then, because during the hot days I was watering it every day. Didn't realize it prefers dry soil. Guess I'll know for the future.

Do you know how long it will take me to get a new plant using cuttings? Can I actually just put the large part of the plant that survived without roots right into soil and it will grow back? I have one large vine with some smaller vines branching off of it which I've been keeping in water. There is however not much vine left at the base where it got split off from the roots.

I've never done cuttings, as I have a forest of the stuff coming up in the spring. But I understand it should work well. I can't imagine a large plant would survive just being thrust back in the soil, but 6" stems half buried in moist soil should start new plants readily. Malabar spinach grows pretty fast when it's hot, but it might take three or four weeks to just get one foot of stem out of that. It will take a week or two just to put down roots.

It is said that malabar spinach needs a lot of water, but that's not my experience. When it's really hot here, I'm watering everything else every two or three days. The malabar spinach may get water once a week. Look for signs of wilt, and water accordingly. It'll tell you when it's thirsty.