One idea that I tested was the living mulch. The idea is that you would grow an understory plant that would keep weeds out but let water in. And supposedly be ok with the veggies that you're trying to grow. I've seen all sorts of ideas that other gardeners are supposedly successfully using claiming that veggie plants thrived, but I have to say that I have my doubts.
I've read claims of growing veggies amid a short growing grasses. Some claim miracle results using clover. Yet others claim the direct planting right into their lawns works great. Yet other gardeners claim they never weed their gardens, they just clip the weeds short, thus the weeds themselves are the living mulch. But my own experience and tests show that isn't quite right. The grasses and clovers compete too aggressively. Even the weeds. The test veggies that I grew using these living mulches did quite poorly compared to the control plants grown without the living mulch. Thus my own conclusion......I won't use grasses or clovers as living mulches.
I believe in shading the soil surface for a number of reasons. Thus I've been interested in various mulching techniques. Presently I use grass clippings, but I've wondered if I could use something for a living mulch that could take over the shading task after the clippings start decomposing. I reasoned that the living mulch would have to be something that would spread and fill in the space. Be long enough lived to survive until the main crop was ready for harvest. Not be an aggressive feeder. Not have an aggressive surface root system. Not grow in such a way that it would smother and kill that main crop. The main crop I am targeting is taro. Future experiments will test other main crops.
Taro does not do well with competition. So grass and weeds need to be kept under control. It is a long season crop taking at least 9 months, often more. It is very responsive to nitrogen feeding at the right time but does not want over-feeding the rest of the time. And it wants moist, shaded soil. I've been growing it using grass clipping mulch, which has worked pretty well. But because the clippings decompose rapidly, they need to be refreshed monthly. That's a problem for taro since it doesn't like you to walk anywhere on its roots. Applying new mulch means that I step near the taro, thus stunting its growth potential.
I finally considered trying sweet potatoes. While the tubers are ready for harvest 4-9 months, depending upon the variety, they can be left unharvested. Sweet potatoes don't form dense root mats. Their large leaves well shade the soil surface. I haven't found them to be heavy feeders, though the extra nitrogen won't kill them either. It sounded good so I gave them a try. But I wasn't sure if the vines would smother the taro.
Guess what. Taro and sweets to together pretty well. At least so far. I've chosen a variety that is a bunch type with moderate runners and good sized leaves. So the main tubers are right under the heart of the plant. By planting the sweet far enough away from the taro, I could harvest tubers without walking on the taro roots. And by directing the vines towards the taro, the sweets act as a living mulch. All sounds good in theory, but would it actually work.
So I planted taro. For the first experiment I choose a taro variety that is a strong grower and tall. And I planted the sweet potato cuttings in a spot that I could access without damaging the taro roots, plus importantly, in a place where I could also access the taro to clean up dying leaves if needed. Well, so far the experiment has been a raging success. But it's only been going along a few months, thus I will reserve judgement to when the taro gets harvested. The taro has been growing strongly. The sweet potato vines have been spreading and covering the surface without climbing over the taro. I initially mulched with grass when I planted everything but have not added more grass mulch since. Very little grass or other weeds have grown through the vines.
Next time I will plant more sweet potato cuttings so that I see faster ground coverage. And I will try several different taro varieties with several different sweets, looking for the best combinations. So far I haven't seen any negatives, but then this has been a rather wet year. Will this method also work for drier years? We'll see.
Here's another combination, a less vigorous taro matched to a less aggressive sweet potato. I'm interested to see how they get along together.......