I lived along a sandy coastal area for many years. Sandy soils eat up mulch...and benefit from it. I would use an assortment of organic mulches at different times of the year...compost, wood chips, bark, pine straw, fall leaves, etc. You won't have to top dress 'constantly', but perhaps three or four times a year as it disappears into the sand.

I would let worms and other macroorganisms work these products into the soil for you...you'll be shocked at how fast it disappears. Just apply occasional top dressings and let natural forces to the work for you.

I agree with rhizo. The more Organic Matter the better until you get the results you want.

You can add some compost as a mulch often, like maybe once every two weeks, and then cover that with another mulch in case the compost blows away. Then when you change crops you can dig in deeper.

I basically live on a sand dune and I can't imagine it being possible to overdo organic matter.
Do you have access to seaweed? Wonderful stuff.
You don't mention whether your garden is in-ground, raised or what.
I've been slowly lowering my previously raised beds as it was impossible to keep the moisture up.
The sides are great for holding mulch in, but my garden beds are generally at or below ground level

Apply 3" or 4" of shredded leaves mulch when plants are 8" to 10" high. Then after harvest turn what's left, if anything, of the shredded leaf mulch into the soil before the next crop is planted. In time you'll have beautiful tilth and lots of beneficials working the soil for you.

My Lake Michigan beach sand soil needs a lot of organic matter, compost, shredded leaves and other yard waste, just to keep the humus (residual organic matter) near 6 to 8 percent. Just keep adding organic matter, to maintain that 6 to 8 percent level, and do not expect much from your garden for 2 to 4 years since the Soil Food Web will need time to get estabilshed and working at feeding your plants.
It took time for your soil to loose the organic matter it once had and the bacteria and fungi and other critters that make up the Soil Food Web so it will take time to reestablish them. Some people have reported good results with things like Compost/manure Teas and spending money on something sold as Mycorrhiza innoculants that you might try if you have more money then time and energy.

A Texas gardener said she had "sugar sand", it eat all her leaves,grass clipping & manure from 12 horses & still did not become a loamy-sandy soil. Last we emailed each other she was still in the good fight. So it can be done, it just take time to build a good basic soil. Raised beds with solid sides,concrete,wood or metal would help hold the compost in.
If you could get a tuck load of loamy soil, that would help. I would go to the site & look at the loamy soil, see that it was something you want in your yard.
I got some great soil, but it was filled with weed seeds, which I beat down in 24 months. But you do not want that if you can help it.

I went from this sandy loam (6 years of barren sun baked soil resulted in loss of loam)

{{gwi:274907}}

To this (in about 2 months)

{{gwi:289844}}

I used store bought bagged compost mixed into the top 2" of my barern soil and then covered in grass seeds covered with a small amount of compost and bagged topsoil to prevent birds and drying out. Lots of weeds in the bagged topsoil but I cleared them out over the year.

The 2nd green picture above was taken about one year and nine months ago so almost 2 years ago. I still have problems getting trees and plants to grow well in the ground. It takes about a year to see results from any tree Ive planted. Anything I plant I always layer OM such as compost, manure, organic fertilizer, pine chips.

This bottom pic is about 2 months ago (same old pic I always show)

{{gwi:274905}}

Since one of the reasons to make raised beds is to improve drainage and most of the sand I have gardened on drains really well a raised bed on sand can become a realy problem. Two of the community gardens around here that serve primarily seniors have raised beds, on sand, and those raised beds are lined with heavy plastic sheeting to help retain moisture. One other communitiy garden that did not line the raised beds with that plastic still has a big issue with soil moisture.

If you have problem areas, you might want to remove the current 'soil' and replace it with soil that works better, some sort of topsoil that contains clay.

Wwhen you say structure, do you mean changing the texture or filth? Soil structure refers to how the less aggregate. In a sandy soil that will be single grain structure. With addition of organic matter you may eventually get a weak granular structure.

*tilth, stupid autocorrect on phone.

*tilth, stupid autocorrect on phone.

ibuzzard,

Come fall you might want to consider making hugelkultur beds.
Around Boulder Creek, you probably have access to free logs.

I just did it in clay (low organic content) soil and my squash is growing great for the first time in that location.

In another bed, I've dug in 20% wood chips and I'm seeing if veggies will grow there well with the addition of lots of organic nitrogen fertilizer. Too early to tell if this will work yet but I'm hoping it is a way to quickly increase the organic matter in one season, while still getting a good crop in the first season.

So, if you were burying wood for hugelkultur redwood would be the best wood. OP lives in a redwood area. I found this comment on You Tube.

"Stay away from Black Walnut (juglans nigra) as it leaves a residue that toxic to some plants, especially tomatoes and potatoes. Black locust, Red Cedar, Osage Orange aka Hedge Apple break down very slowly and will not "rot" for decades...why they are used for fence posts. Many other pines and spruces should be avoided too as they may acidify the soil... Maple, Ash, Dogwood, Hickory, Oaks, Elm, Yellow Poplar and fruit woods seem to break down at a constant rate....contd." but there was no more comment and the account was closed down.

So, if you had like a rabbit and used pine bedding that would acidify the soil? I want to acidify my soil. But, it probably is too good to be true. Also I don't have a plentiful source of free or cheap redwood or pine wood and those pet beddings are very expensive. Maple, Ash, Elm, Yellow Poplar. Those are east coast trees. We are have pines and redwoods in California. But, I don't access to them in an urban area.

Hugelkultur might be a good idea someplace where there is enough material and where the gardener has enough time to allow it to happen. It can take somewhere between several months to several years before a soil made that way will grow plants good enough to be used for food. Colorado may not be the best place to look for wood waste to do that. Finding adequate amounts of waste organic matter can be a challange.
But, all that soil needs is adequate amounts of organic matter, compost, yard waste, shredded leaves, straw, spoiled hay, whatever can be found, preferably for free.

in addition to adding organic matter as others have said, grow cover crops, if you can, to add organic matter. Grow Oats and peas in the spring, till them in once they start flowering (with benefit of adding nitrogen from the peas which are legumes so fix nitrogen gas from air); grow buckwheat in summer until it flowers then till it in (this also increases the bioavailability of phosphorus); grow rye and vetch in fall, and till it in in the spring (also adds nitorogen as vetch also a legume)' etc

OP is not in Colorado, look back at the first post, he is near Santa Cruz mountains, a redwood forest. There should be free redwood logs to be had.

Isn't vetch invasive? I grow poppies that I can later compost, not so invasive as a vine that can be hard to remove from the soil.

My own experience with hugelkultur is that it works immediately, doesn't need time at least for squash plants, which is what I planted. And my plants are dark green after adding a fair amount of liquid organic fertilizer.

I wouldn't use redwood trees, they take forever to decompose. I used pines, they decompose faster than most other wood. Didn't worry about pH, my soil is alkaline. If you have acid soil, you could just dump some ashes in the soil when making the bed. Also the irrigation water is alkaline.

In the California bay area, if your willing to drive you can pick up all the logs you want free at 1 Arastradero Road (off Alpine), Portola Valley. The tree service dumps them there for anyone to come and pick up, bring a chain saw though.

One simple method is to just bury one stump in the ground about a foot below ground level and plant on top of it. My cucumbers planted that way are doing great. Interestingly they have not wilted even once, even when it got to 95 degrees. I think the roots have covered the stump top and are able to wick water extremely well because of this. My other cukes with just soil beneath them wilt in the heat.

Here is a link that might be useful: McClenahan Tree Service

ibuzzard - yes, constantly adding organic matter after harvest before the next crop. To speed things up bring in a lot of organic matter as manure + bedding to compost in piles set aside from the current gardening beds. Then after harvest rake those on to the beds if you let some lay fallow or put what is crumbling & dark brown on beds you plan to replant right away.

It takes awhile to build enough compost to cover all the beds at all times, but with diligence you can do it. The small animal manures like chicken & rabbits are potent, but not the quantity you'd need. Get a hold of some horse manures and you'll be able to speed up the process. Ten years of using chicken, duck & rabbit manures from our backyard animals (Plus liberal amounts of used coffee grounds + shredded leaves mown over on the lawn in fall. Plus our kitchen waste compost bin contents.)... didn't up the soil organic matter content as much as when we started adding horse manure as well composting first in piles or spreading in fall on fallow beds.

Volume made a huge difference though I was quite skeptical in the beginning, afraid of weeds & then learned about the herbicide residue in some hay fed to livestock. I made sure we used manure from horses fed alfalfa hay instead.

Now after at least 3 years of horse manures we no longer need 6-12 inches of it added in the fall to break down. The soil is light, fluffy and diggable with hands rather than pickaxe like before.

Under about a six inch depth of grass (roots) I have pure sand. I've been told that I could dig up the sod, turn it upside down and then fill with good soil and the grass will not return (I'm thinking of doing this for bulk in the bed base as soil is expensive here). I have a large lot and am only putting in large flower beds. Is this possible?

lizzdenis, that depends on the grass. The wimpy grasses, Blue Grass, the fescues, and perennial ryegrass, will die if turned over while the "weedy" grasses, Quack grass and such, will eventually grow back.
What your sandy soil needs is organic matter which will fill in the pore spaces between the sand particles and hold both moisture and nutrients in the root zone.