This is an old post but it’s still relevant now if not more so. Actually asparagus roots from healthy certified disease free crowns that have been in the ground for a number of years can grow roots up to 10-15 feet deep (not 12”). It is highly dependent on the variety and the soil and the nutrition and water provided. It is highly recommended to not plant them where the water table is closer than 4’ to the surface. Asparagus can live, provided disease nor pests get them, for 20-25+ years but typically new beds are established after 10-15 years to get the biggest, fattest spears. And commercial folks do it much sooner. I have friends who had 2 beds over 30 years old last I heard; they have died now so I don’t know the current status. I would imagine the spears might be getting a bit thin and crowded by now. It depends on care, if thinned out, the weather, soil, not over harvested, fertilized, getting the beds right before planting, not harvesting too early before the crowns have built up good strength, and getting certified crowns (no diseases like fusarium), etc. and following advice like if the spears are under a inch in diameter, you don’t harvest, they are too weak. However, I would in no way, shape or form plant asparagus over sewage leach fields. You might want to eat them, but not me. Yes there is a lot of nitrogen in poo but the amount of human pathogens will be heavy not to mention if you have put any chemicals, medications, cleaning ingredients, pet poo/litter down the toilet or drains — the plants will take these ingredients up - again you might, not me. Of course, you aren’t suppose to put those things down septic systems but plenty do. Any meat eating animals like cats, dogs will generate very nasty pathogens and serious diseases in people (think flushing kitty litter or accidents). There was some testing/trials done in NY where the soil was heavy clay over gravely clay subsoil and even in that tough conditions roots reached 2’. It’s like tall clover, left in place and just cut back with a scythe or allowed to die naturally and come back up — roots can go down 10-15’ and help break up hardpan. Plus the green material adds a layer of rich nutrients to the soil. I like to do this 1 1/2 years prior to my starting a 2 year schedule of bed preparations of green manures/cover crops finishing the final fall with a covering of Dutch white short clover before planting final perennials, shrubs, etc. the next spring. When the clover dies down from the cold, I cover the beds with 6-8” of top quality tested dairy alfalfa hay (no grass hays or mixes of those with alfalfa, just straight alfalfa. It will test very high in nutrients and protein. It should be tender, bright green, crumbly, rich and full of tiny little green leaves which are the gold that adds tons of nutrition to the soil and keeps the earthworms working the soil over the winter. Don’t loose those little leaves. Open the bale over the bed and wrap it in a tarp if carrying in your car or back of the truck so they don’t blow away. It’s what cost so much — you want them all. Come spring, work it all in to the soil by turning it over with a spade fork, etc. so it can further decompose. But never ever till wet soil — you ruin the texture for decades. No matter what you see or read, asparagus don’t do well in containers, not even raised beds unless they have decent native soil underneath to grow into. I have never in almost 50 years seen asparagus crowns dug up that they weren’t at least 5-6’ long. You can work the native soil if decent and then build 2’ deep raised beds with good top soil. It’s like tomatoes, especially indeterminate, but also regular determinate - I have had the roots fill a 32 gallon trashcan easy. I believe if properly grown, a big indeterminate would fill a 40-50 gallon can planted Mother’s Day, and dumped Oct/Nov. Sure you can grow them hydroponically in 5 gal dutch buckets but they are being fed and watered continuously and the roots get massive and they don’t even have to go anywhere to find food and water — they are bathed 24/7 in nutrients. Note, try to get good rich top soil and leaf compost and if you can find it - goat, rabbit or sheep manure to mix in. Bagged top soil is bark, compost made from bark, and/or pest Moss with perlite, etc — basically potting soil. You will need to lime after testing as those ingredients are highly acidic (3-4 pH) and asparagus like neutral to slightly alkaline pH (7-8 pH) not to mention, bark will require more nitrogen to be used for the 3-7/8+ years until broken down completely. Soil test will advise nitrogen, phosphorus , potassium deficiency or overage in addition to lime and calcium, etc needs. Find bulk aged leaf mold — from aged leaves and little to no bark or wood. If you can’t and can’t make enough of your own, then you will need to spend several years green manuring/cover cropping until your soil is rich and crumbly textured. Don’t forget the rabbit, goat or sheep manure. Horse and cattle will give you too many weed seeds, possibly too much carbon that has to age and ties up nitrogen — not as bad as bark but a year or two. Cattle and horse litter will contain grass hay, sometimes full of weed and gp grass seeds, sawdust/shavings from their bedding, and more worrying is some of the new hay herbicides in the past couple of years stay in the hay even after being composted. It is grown, cut, baked, cured, eaten by the animal, travels through its gut, the manure is composted and aged commercially and still shows up in the finished compost and either kills or stunts plants. They think they have it figured out but some farmers may still use these — I can’t think of the names of these new herbicides but there were plenty of articles on the issue and are called high residual or long lasting herbicides. It ran a few commercial bagged compost folks out of business a couple of years ago. The first time I heard about the issue was on Growing a Greener World but I had horses for decades, and was around hay producers and cattle for years but this was a really serious development that no one expected — these were new herbicides. And they are nasty herbicides to stay active and effective for that long a time. The EPA and USDA and whoever else did a poor job on allowing these to gain approval. A comment on bark being used in compost or for mulch, it can be free bark, interior wood of the trees, it can be from torn down houses, can be from remodeling jobs including lead painted trim or boards, can be from pallets, discarded recycled furniture, you name it. Pallets can have spilled chemicals on them as can other recycled woods that have been sprayed with pesticides and termite treatments. In fact many mulches used around planting beds may be treated too which is a good reason to not use in your vegetable gardens plus they aren’t aged/composted enough to kill diseases or pest eggs. Many times trees come down or are taken down because they are diseased — the diseases come to your house in the mulch. If gotten free at the local dump, chemicals flow in rainwater along the surface and are absorbed by the mulch piles. And no matter where the mulch or bark product comes from, you will always need to add lime and extra nitrogen to make up for the high acidic pH nature and because it ties up the nitrogen while it’s breaking itself down but again testing is needed to know how much to add.

Here are two agriculture university composed asparagus commercial production guides — that speak from A-Z on growing asparagus for sale including a little on seeded transplants and through to harvest plus making the beds, planting, fertilization, etc. You can probably find one specific to your state by searching “commercial asparagus production” and your state name at the beginning or the end” You can also find these for other crops too. I haven’t looked at all of the other links, but I start with what the commercial growers do and then adapt for home use. There are way too many people who started growing last year or even a couple of years ago and who go on what Joe Smo on YT said. If JS’s other plants look yellow, sickly and spindly, I will pass on his advice. Same if you never see his actual plants, or harvests, or any firm time tested advice. If they have grown long enough to be giving decent advice, you will see his plants and the healthy produce ready for harvest — at least at some point. For every 1 knowledgeable gardener with a YouTube channel — there are 100+, gosh maybe a 1000 that need to not be giving advice to anyone until they better know what they are doing. You don’t have to go to college to be a great gardener but you do need to be wise enough to use your brain to research the proper resources- it’s easier than ever to research and find appropriate advice. Too many people think they have seen a pro build a deck or landscape a yard, put a roof on, and all of a sudden — “I can do that and make all that money”. And they can’t - no experience or teaching. We have lots of so called want-a-be contractors like this. And what’s worse, here they are giving advice on subjects they don’t know to other newbies and the problem compounds itself with lots of wasted time, money, materials and potential legal issues or injuries. OR like in this case, someone getting some horrible, maybe fatal, maybe contagious disease — or being killed, getting cancer, or otherwise made very sick from some dangerous chemical or medications flushed down the commode and his asparagus plants picking up the whatever and ending up on their dinner table. My thought is if you don’t have anywhere to garden except your septic system, then buy veggies from a local organic market. In fact, you aren’t suppose to do anything over septic fields except plant grass, no tilling, plowing, no driving heavy equipment over them, etc. in terms of chemicals, we already have issues with these things ending up in our rivers/oceans from public sewer systems. You know, it’s a shame, but a lot of younger folks don’t know what really well grown plants should look like — they haven’t seen many. And many of the parents haven’t farmed or gardened much either. For the youngest, their grandparents might not have farmed or gardened much either. These young folks follow what they see by some of these landscape companies do like crape murder, volcano mulching, incorrect shrub pruning, bad planting methods, etc. Many of those companies are those someone started out of the blue with no trained arborist, landscape architect, no trained, certified chemical technicians, no understand if nutrients, pH, EC, TDS, DO, or no understanding of even basic agriculture or horticulture. They lost their job, started cutting grass and the next thing they are offering services, the just don’t really know about. I have these guys show up who don’t know the difference in a crape myrtle and a lilac or even a deciduous azalea. I was in Lowe’s a couple of weeks ago, and a guy asked me about some plants — he had customer “said a buddy told him to ask like $1000 dollars (plus plant cost) based on her upscale neighborhood to put in all these annuals, perennials, and a few shrubs. She told him what she wanted — but he didn’t know impatience from vinca nor boxwood from azalea or gardenia. The poor guy couldn’t read - said he dropped out of school in the 5th grade and moved to Canada, then Mexico with his dad — basically got by - looked to be 30. His Dad said he had never finished school and it worked out fine. I’m thinking you are floating from country to country with temp jobs, dragging your son and getting around no education , no real home, — didn’t sound good to me but I didn’t say a word on that issue. I was shocked and told him, I would go back and tell the woman the issue and say he really needed to stick to her grass and maybe she could find someone else for all the rest. He didn’t know the plants, didn’t have a clue on preparing the beds, nor actually planting or taking care of them and worse, couldn’t even fake it by reading up on the Internet. I sorta gave him the guilty spiel - “how would you feel if someone “ripped” your mother or grandmother off like this”. Whether it worked or not, will never know, hope it did.

http://www2.ca.uky.edu/agcomm/pubs/ho/ho66/ho66.pdf

https://conservancy.umn.edu/bitstream/handle/11299/198098/Asparagus production guide.pdf?sequence=1&isAllowed=y