Preparing a tomato bed.

[zeuspaul]

I am prepping a new bed adjacent to my container garden. The main garden is a long walk and I am feeling my age.

How deep is too deep? I am loosening the soil down about 20 inches. Below that is impenetrable soil. If I want to add amendments what should I do? Osmocote down about 12 inches and organic amendments, peat and or manure down about 6 inches? Anything deeper than 12 inches?

I would classify the soil as sandy loam more on the sandy side.

[Shule]

@zeuspaul

Is there a reason you suspect that loosening the soil too deep might be a problem? Planting too deep isn't always ideal (I've had faster growth if I transplant the roots within a foot or so of the surface, compared to 1.5 to 5 feet), but I've never heard of a problem with loosening the soil deep. Most of our soil isn't a sandy loam, though.

[Cole_Robbie]

The roots will take the path of least resistance and grow wherever the soil is loose.

[zeuspaul]

@Shule I don't have a good reason. The no till crowd might argue interruption of capillary action?

20 inches is what I am limited to unless I want to use a jack hammer. I am concerned about fertilizing it. Too deep- will organic fertilizer be ok? I was guessing it might get more oxygen higher up. And is there any benefit to deep (20 inches) synthetic fertilizing? Wouldn't the nutrients navigate downward?

I vary how deep I plant the tomatoes. I plant deep enough to pack a little soil around the stem to support it. I plant deeper later in the season to better access water.

[brownrexx]

Instead of planting deep, some people lay the seedling stem horizontally in the planting hole so that roots will grow all along the stem.

I don't add fertilizers. My soil is full of compost and organic materials.

[bower]

My soil here is shallow.. 20 inches sounds great.
I never fertilize deeper than that. I put some ferts in planting hole and dig them into the bottom and surrounding, so not much deeper than the seedling is being planted. This is how we do tomatoes in ground at the farm sometimes too if ferts are to be added. If you're using bone meal to encourage roots I would mix that into the lower depth of the soil, as roots will seek it out - I have seen seedlings concentrate their roots in the top half of a beer cup where the bone meal wasn't mixed down. So the higher placement might slow root extension into the depth at least short term. For general amendments that break down or get consumed in the season, (other than planting hole) I usually put those within 6 inches or a foot of the top on the expectation they will migrate downwards. At the farm when we add kelp meal or chicken pellet, it is scratched into the top few inches. We do get a lot of rain here, but that's how we do ours. Compost or horse manure gets dug into the top foot or so of soil.
It's possible that amending your top soil may affect the hardness of that subsoil over time... IDK.
The no till approaches which just add material on top, are famous for softening up the soil below.
But there are so many kinds of soil and subsoil, I'm sure there are different approaches that work best for different things.

[Paulf]

The soil is the precious life-blood for any and all things you plant this year. Before you start digging away, there are a few things you should know. The purpose of tilling is to mix organic matter into your soil, help control weeds, break up crusted soil, or loosen up a small area for planting. You do not need to till or break up the soil very deep; less than 12 inches is better.

Tilling too often or deep can do more damage than good to your soil. Enthusiastic rototilling done too early in the season can result in the earth's becoming hard and unable to retain moisture. Any heavy tilling when the soil is wet is also destructive to soil structure. The soil will become terribly compacted and dry out too fast.

I used to go as deep as possible until taking Master Gardener classes and had a soils expert explain what happens to the garden with too deep tilling. Twelve inches of digging topped with 6-8 inches of mulch should do the trick.

[brownrexx]

We till once a year in the Fall. I learned my lesson about Spring tilling when the soil was too wet. I ended up with huge, hard clods of soil that didn't break up all summer. Now I have nice, fluffy soil that I rake smooth and allow to settle and rest all winter. We only till to the depth of the times which might be12" and I apply a deep straw mulch on top.

[zeuspaul]

Thanks for all the helpful responses.

Most recommendations I have found for fertilizing and amending are for 3 to 12 inches deep.

Then there is double digging:

Double Digging: A Hallmark of French Intensive Gardening

Mark and dig one trench, double the depth of your shovel or spade.
Set aside the top soil in a wheelbarrow.
Spread compost or soil amendment. This is an ideal time to add phosphorus deep in your soil where plant roots will be able to access it. Use soft rock phosphate or a high phosphorous fertilizer.
https://www.groworganic.com/blogs/artic ... -gardening

Gibson: The benefits of double-digging garden beds

“Double-digging” a garden bed is a good first step toward reducing soil compaction, improving tilth and solving the nutritional deficiency problems common in desert soils.

A friend and I once helped establish a community garden here in Pinal County. The donated site had plenty of space for multiple beds and water was readily available. He chose to double-dig his plot of ground before planting while I took the easy route. His sweet corn and other vegetables were larger in size than those planted in my plot, and, to top it off, he harvested more produce. It made me a firm believer in double-digging, and I have been recommending it ever since, particularly for first-time gardens.
https://www.pinalcentral.com/trivalley_ ... e33af.html

Most recs I find for double digging is it is a one time thing used for a new bed as long as you don't walk on the soil. I have no plans to double dig this new bed because it seems like too much work for me. However double digging is about 20 inches and I can get that with my earth auger. Organic matter and ferts are placed deep with double digging. Specifically there are recs for deep phosphorous to stimulate deep roots.

[zeuspaul]

How Deep Do Tomato Roots Grow? The Definitive Guide

How Deep Should My Raised Bed Be?
If you are looking for a quick answer because you are building a raised bed or if you want to know whether your existing raised bed is deep enough for tomatoes, you will be glad to know that just 1 foot (30 cm) is sufficient.

Notice that I say sufficient and not ideal. The ideal depth would be greater than 2 feet (60 cm) because, in general, tomato roots can grow anywhere between 2 and 3 feet, even though around 2 feet is more common.
https://dengarden.com/gardening/How-Dee ... Roots-Grow

[Uncle_Feist]

Tilth, nutrients and moisture and are the most important things to plant growth and productivity. Deep digging is detrimental in most cases. You either create a hole to hold water and suffocate, or you disturb the natural ability of the layers of soil to wick moisture.

[zeuspaul]

In my case there is no natural soil. I am trying to create a soil structure. Almost nothing will grow in this *natural* soil. It is a compacted sandy gravely hardpan. I have placed some sandy loam on top of the hardpan from another part of the property. It is on a slope so water should drain to the lower side so I shouldn't have a bathtub.

[Uncle_Feist]

In my case there is no natural soil. I am trying to create a soil structure. Almost nothing will grow in this *natural* soil. It is a compacted sandy gravely hardpan. I have placed some sandy loam on top of the hardpan from another part of the property. It is on a slope so water should drain to the lower side so I shouldn't have a bathtub.

Sounds like that soil may fool ya as to it's ability to sustain, and produce. As long as soil isn't prone to waterlogging, it can be very productive.

I have an area of land that is gravely and hard to work, and it also pacts like concrete after a rain, but never fails to produce a bumper crop. Even root crops do exceptionally well in this soil. Stagnant soils that hold water are the enemy. Mulch and nutrients are easily applied for good growth, but excess water is the devil.

[brownrexx]

My soil is heavy clay but after years of tilling organic materials into the garden, that soil now looks like decent topsoil and produces good crops. Adding organic material to the soil was the answer for me.