Do soil nutrients travel to the surface?

Question

I've built four additional raised beds for my garden, and put a lot of tree branches and cow manure at the bottom.

The problem is, the beds are two feet deep (24" sides, I mean), and I had intended on filling them to within 4 inches of the top with soil (with woodchips on top).

Basically, if I have eight inches of soil on top of the tree branches, and if whatever I plant in the beds don't have roots that reach that deep, do the shallow rooted plants still benefit from the nutrients?

Or should I churn up the beds in three years to bring the nutrients to the surface?

(A quick google shows that tomato plant roots go 12+ inches, so I probably don't have anything to worry about, but am still curious. Also, I'll be sure to put good material in the upper eight inches, not just soil.)

Answer 1

I'd recommend using a raised-bed method known as "Lasagna Gardening."

Basically, you start with a "smother layer" of wet cardboard or newspaper at the bottom of your bed to kill off and block any plants from growing up into the bed. Then you lay down repeated layers of carbon materials (leaves, shredded paper), nitrogen materials (fresh grass clippings, composted manure, ground soybean meal), and dirt/compost (for the composting bacteria), with a layer of ash on top.

By doing repeated layers, as this layered active compost pile breaks down, all of the nutrients will be available no matter what level the plant roots are at. Also, since you plant while the composting continues to go on, the soil feeds/replenishes itself as it continues to break down into more compost.

It takes a bit of prep work, and you have to set it up in advance of planting (the pile has to partially to mostly compost before you plant), but it requires no tilling, once set up, the weeding is easy, the loose nature of the material is very friendly to root growth, allowing for more intensive plant spacing.

Weeding is also a snap, because of the loose materials, and you get really robust results. The only drawback is the preparation of the beds, which takes work and planning.

Here is one link to a site, but a simple Google search on "lasagna gardening" or a search of the local library catalog will give you all the info you need.

Infiltrating Landscapes Blog

Answer 2

You'll be just fine.

Don't go ripping up what you've done due to contrary opinions - Start another couple of beds and compare results if you really want to investigate alternative methods, but having started down one road, don't over-work yourself on second-guessing. While I tend to agree that the hugelkulture approach has gotten a bit faddish, I don't agree that there's only one true way and it certainly seems to work for enough people to have become faddish in the first place. So roll with it and see how it works for you, rather than ripping up what you've done already. I guess if there are "additional beds" you already have some beds you can compare to that were done differently.

Nutrient distribution will be accomplished by worms, mostly, and by continuing to add new materials to the top while letting the bottom be.

Answer 3

The majority of plant roots are only within the top 4 -6" of the surface. Roots that go deeper are for support not uptake of water and chemicals. Nutrients/chemicals the plant needs to continue photosynthesis in order to make its own food are taken up in a liquid solution.

There are more than a few problems with your bed formation. Un-decomposed organic matter; cow manure (if it smells like poop it still is poop or rather it is not decomposed) and branches cause the micro and macro organisms in the soil to go dormant while the de-composer organisms do their job decomposing something that was once alive and now dead as these soil organisms need decomposed organic matter to feed upon...so they just take a long nap and leave remnants of themselves to wake up when this job is done enough for them to have food. De-composers, primarily bacteria and fungus, use a LOT OF NITROGEN to do their work making nitrogen less available to plants, not more. So, no, the stuff you put UNDER your beds and even if you put it on top of your beds will not be adding nutrients to your soil until it is decomposed. Those nutrients are for the soil organisms that work symbiotically with plants. This explanation is pretty basic but I hope that makes sense.

The next problem is a perched water table. This has nothing to do with your indigenous water table but the principle is the same. When you water your beds the SMALL pore spaces have to become saturated BEFORE the water will move into the vastly LARGER pore spaces of your debris. Thus the drainage is greatly restricted. Saturated soil for any length of time will cause root rot, promote 'drowning' of plant roots as air needs to be present for gas exchange. Hydroponics is water loaded with oxygen/air working with roots grown to deal with the world of being under water and fairly sterilized where garden soil certainly is not...which is okay for the garden as there is a balance of beneficial bacteria, fungi, soil organisms that control the entire system for their health and subsequently the plants they subsidize (?). Hydroponics and pots are completely artificial where we have to play nature's part. Gardens are still artificial but easier to use natural processes to assist us humans.

You are actually creating one of these Hugelfugel things that have become sort of a fad. Not the correct spelling, I'll fix that in a few but I would dig your beds up and remove this stuff. Decomposed organic matter on top of your beds works WAY better and is easier on you. Soil organisms will flourish come up to the top and eat this decomposed organic matter go back into the soil (4-6") where they still have pores filled with air and poop it out, mixing it in for you! Very cool thing and keeps your soil alive, draining well and adding fertilizer is NECESSARY to replace the chemicals necessary for healthy plants that WE striped off our soils when we blast in and disrupt entire ecosystems. But fertilizer is not food...plants make their own food. Less is better. Best when we do soil tests and know which plants need more nitrogen and others less nitrogen in relation to phosphorous and potassium and then there are the micro chemicals that are necessary and the pH which is another big big deal that again differs with the individual genus and species of plants...