Harvesting premature, but viable seed

In the interest of saving time and space in the garden, often the gardener will uproot the flowering plant before the seeds are mature and finishing the drying-down/seed-ripening process indoors or on the ground outside.
The still-maturing culled plant can be 'mulched' straight onto some open soil on a new bed and the seeds will ripen, drop off and sprout through the stems of its parent over time.

This cutting of corners saves time, space, opens up new opportunity in the garden and increases seed supply quicker than waiting for full ripening in situ.

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I use this method to spread my various leaf mustards, bok/pak chois, lettuces and tomatillos to new beds.
As soon as the first seed pod/cluster on a plant is ripe, the plant can be pulled and dried inside or mulched over tilled soil with the seeds ranging from an estimated 20-80% germination rate.
There is of course a lot of variability in whether an individual specimen will seed quickly and all at once or drawn out with repeated flowerings.

I've also had good results with pulling marigold, salvia, hemp and coriander early, finishing them off in paper bags.

If memory serves, I've read this method is used for many annual flowers/herbs ... I think I recently read Carol Deppe say she picks Beans early if the weather was getting wet and ripens them indoors wrapped in a tarp.
I believe many weeds, such as fireweed are also adept at ripening seed after being uprooted.

Does anyone have tips for which plants do/don't manage to set ripe seed from an early culling?
Any of the grains have this trait?

Grains can definitely be harvested early. Will Bonsall has some interesting thoughts on that in his gardening book for wheat. Interesting because I have previously read about the superior flavor of land race wheats hand harvested. Will has actually hand harvested his wheats does so routinely and recommends doing so early for superior flavor.

Wildland seed collectors sometimes have to harvest early to avoid shattering, insect damage, or another trip to a collection site; as travel and time spent not picking are wasteful. One of my mentors said that the "soft dough" stage is acceptable.

Joseph has mentioned that corn harvested in the milk stage is viable. I've also read this from other sources including a survivalist post on how to get vegetable seeds in an emergency. If you wanted to you could save an ear of raw sweet corn for seed. Note: some conventional sweet corn is now GMO, so please don't do this with random grocery store corn.

There are some distinctions to be made though. When pulling a whole plant at least some of the seed may be able to ripen fully and perfectly.

Then there are issues of seed quality and here I will make an argument for harvesting seed perfectly. Much of the seed we buy is harvested early and is of relatively poor quality even if the germination rate is high. Carol Deppe writes about how we can grow better seed than we can buy. That's because in our gardens, with care, we can harvest it to perfection. So the big problem with poorly matured seed is going to show up as longevity issues where seed that should store for many years only lasts a few and poor seedling vigour.

That said when doing an adaptation breeding project for a crop you could not previously grow and you get some half viable seed as Joseph has written about for Landrace Plant Breeding I believe the correct and technical term is: Woohoo!

Also if the weather is going south and you will otherwise loose the seed crop by all means pull the crop or do what you must to save the seed crop. Or if you are out in the wildlands and the seed is ripe enough but you know you will not be back again at the perfect time, harvest some now.

With wildland seed these seed quality issues are important and often overlooked. Many wildland land managers save their seed for a long time without regard to how it was harvested. If you harvest seed early make a prominent note to use it promptly no matter if it is wildland or horticultural seed.  

While my goal isn't to harvest seed early, I have done it in certain situations. My homestead farm is at a high humidity, moist location. Thus bean and pea seed will sprout right in the pods long before the pods dry down. So before I purchased a small piece of land for my seed production farm, I use to harvest the peas and beans early and dry them inside my house. I also produce gourds for gourd artists. I discovered that the gourd seed they got from their green but mature gourds would germinate, although I don't know the percentage of germination.

One important thing I noticed when doing this.....and it's the reason that prompted me to buy a drier location for seed production......the seed doesn't stay viable as long as properly matured and dried down seed. The shortened life of the seed was an issue for me. Some of my bean varieties are grown only every other year in my farm. Thus I saw low germination rates, sometimes close to zero, with early harvested seed. Yes, I could have changed my planting routine and grown every variety every year, but I also sell my seed. This requires that my seed be good quality, not short lived.

I still have times where I harvest young seed and immediately replant it. I'll do this with beans. Someone will give me a handful of beans of a variety I haven't tried yet, which I'll plant in a small bed. I'll harvest those as soon as they are ripe enough, then go plant a larger production bed. That way I can turn a couple dozen seeds into handfuls for sowing.

Thanks for the great replies!

Picking seeds early is definitely not ideal from a storage standpoint, especially in the tropics. Similar to how fruits harden their outer skin at the last stage of maturation to ensure longevity.
But free seeds, in the garden, that can be flung somewhere to sprout - woohoo, indeed.

Keep in mind, the vast majority of gardeners cull plants prior to flowering and re-buy seed.
Shouldn't be so hard to convince them to allow just a bit of flowering for the beneficial bugs and a few early seeds.

Sounds like early picking is a necessity for beans in the tropics - I'm sure to try this next time we have a really humid season.

Seems logical that young-harvested wheat would taste better, possibly at the expense of nutrition.
I wonder if secondary harvests could be achieved from a plant that has had an early picking.

As noted, the more biomass left attached, the more likely the seed is to continue maturing. I tend to leave the roots in the ground, but keep the rest in one piece to funnel it's energy/moisture to the seed head.

To fully satisfy my curiosity, I may have to grow a smorgasbord of grains and see how viability fares in response to early harvests.
For some reason, I think sorghum might handle it particularly well.