When is the best time to plant these, how long should I leave them in for, what's the best way to cut them down and incorporate the residue, and how soon after can I plant ordinary crops (veggies and flowers)? Will they grow back from their roots if not dug up and pulled out completely? I need a recipe for the whole process, and appreciate also any experiences from those who have tried this.

Repeated plowing or tilling often exacerbates the compaction, so I'd avoid doing much more of that. Any plant roots that penetrate deeply will help to break up compacted soils and 12" isn't all that deep......I'd expect to see gradual improvement from just the routine growing and harvesting of crops.

And FWIW, I'm not sure I'd agree with the previous post. Unless there are other issues not disclosed, loosening or breaking up compacted subsoils is not necessarily a bad thing and often desirable.

I think we have a different definition of tap root, too. I don't think of alfalfa as having a tap root. It makes a good cover cop because its a nitrogen fixing legume.

Why would you need to break up the soil deeper than 12"? I grow native plants that do set roots deeper than that, but most typical garden plants don't. And the plants that do have deep roots, don't need any help penetrating hard clay, they've been doing it for centuries.

JPW, many garden vegetables can put down roots several feet -- here is a classic study. Johnny's describes alfalfa's taproot.

There have been a few threads touching on this subject, but they seem to contain contradictory information on what crops work best for this purpose, how long they need to be left in, etc. This study contains some of this information, but has gaps.

Has anyone tried to use deep-rooted crops for this purpose?

If you're into trees, than more the reason to not worry about the subsoil. Trees are strong with roots. So just prepare your topsoil nicely, make raised beds if necessary, and leave the (often)nutrient depleted subsoil alone. Go up instead of down is the better way to go.

I didn't say that alfalfa roots don't go deep, I just said I don't consider them "taps".

I have hard pan and like'd to break that down so the winter rains retain more of the water. We get little rain outside of the winter season and it tends to overwhelm the watershed with all the streets and development.

What can I do to break up this hard pan and bring a greater capacity to retain water on my little tract home piece of property?
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The tried and true method for loosening clay soils is with the addition of organic matter, either through the use of compost and other organic mulches or the planting of deep rooted cover crops or preferrably both. It is not an overnight fix.....improving soils is a longterm process.

rott, have you considered a rain garden? A rain garden is one that is designed to limit runoff and utilizes plants, often natives, that will help to filter pollutants as well as improve soil conditions through their growth habit and root structure. Just like any other type of garden design, they can be extremely attractive if well-conceived plus they are ecologically sound and feature a degree of sustainability that is typically missing in other types of ornamental plantings. If you wish to grow edible crops, these may be best addressed via raised beds (filled with imported soils) - while not the same concept behind a rain garden, raised beds will also have the capacity to absorb and retain moisture and limit runoff.

Alfalfa and yellow sweet clover need to be spring planted...best with an oats nurse crop. The legumes then might need to live for much of the second year for best root work.

I cant find the studies I have read about gypsum. But I will tell you it does make a diffrence in how hard the soil is compacted. My soil was so hard that after discing i had to have a farm tractor come in and break up the clay more. I have a commercial tiller that would not even start on it. After 3 years of gypsum and lime I can now shuvle or till with my tiller. In another year or so I hope that it continues to work. You should always consult with your local agg ext office. They where the ones that reffered me to my regiment.

ps I had been working the soil for 2 years prior with just leaves with almost no results.

Thanks for the reply. I don’t have the resources to invest in a rain garden right now. All but one of our downspouts empties on to our property either directly or across the driveway and then onto the grass. I’ll divert the last one from the street before the season starts in earnest.

The lawn out front slopes away from the house and I’ve noticed when I’ve left a sprinkler on too long during my weekend deep watering routines it will leak through crack in the pavement to the street and quite some distance from the sprinkler.

We have a winter rainy season and remain pretty dry the rest of the year. So we get a lot of rain during one season and our soil out front just isn’t holding it in.

I planted a couple of trees out front and I think that’s starting to do the trick on one side. The other side has an old tree right smack in the middle.

I’ve been propagating California poppies from an 89 cent pack of seeds I bought as an impulse buy in a drug store some time ago. I threw some seeds around when we first moved in and from the couple that thrived we now have them spreading about as I harvested the seeds over time. I go around and trim them in an attempt to keep them going all year long so their taproots keep running deeper and become more substantial. Time to spread a bunch of the seeds I saved now that it’s the end of November.

One of these days I’ll find some other suitable natives to plant. Native California plants offered are often Northern California and not always suited for our hot dry spot between the desert and the coast.

For gardening I’m probably going to go down the container path. Our garage is in the back so a lot of ground is taken over by concrete. The rest of the yard was already planned and planted when we moved in and the open grass area is needed for the dogs.

I haven’t figured out what to do with the lawn out front. I’m having troubles with the ‘well conceived’ part. In the meantime I keep the watering to a minimum and alternate between grass cycling and harvesting grass clippings for feedstock in the digesting bins I maintain for our yard clippings and kitchen scraps.

to sense
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I suggest a couple options. One is planting "summer" alfalfa with oats in the spring. The oats help to prevent weeds while the alfalfa is getting started and the oats straw makes good organic matter. The alfalfa is considered as a one year crop. You can get this from Johnny's.
I wouldn't worry about mowing[mulching] till the next spring.

Fedco sells oats and sweet clover for a one year or 1½ year cycle...mow when the sw clover dies in August or later. Mamoth Red Clover can be treated the same as SW clover.

I think that the fastest answer is daikon forage radishes....spring planted and a second crop planted in late summer.

Rye is a good turf crop but not tap rooted. It is fall planted and a bear to handle in spring. Small areas can be clipped off by hand in spring and then easily killed by tilling.