Marine bulkhead construction completion and soil prep?

I'm gonna have to do a large portion of a backyard landscape. It's getting destroyed due to a canal bulkhead complete replace and I need to start thinking about ideas and then plans.

The construction is now done, but, before anything else there's a considerable amount of fill needed.
But, some specific questions on the salt water canal dredged back fill (South shore, Long Island, NY)

-The back fill and composition of the existing landscape soil is mostly sandy, but there is a large amount of clay that was bucket crane dredged backfill. I'm concerned as to things being able to grow well in it?

-Particularly in large areas (aprox. 5' x 8') that are all clay and deep (not sure how deep, since was dredged) that will have about 1' of topsoil on top? There is at least another 1' deep and all clay, so I'm concerned that a "clay pan" of sorts is being created and will cause drainage problems and not let roots grow down through the clay.

-Was thinking of making a large portion of what gets ordered be compost, since this is good to amend to clay soils and sandy soil in general conditions?

Thanks

physeek, regarding the clay areas, I recommend a raised garden because from what I've read it's difficult or impossible to change the composition of clay soil in the long term. I don't even try. Our deciduous and coniferous shrubs grow well in clay soil, but the wax begonias are not as large as they could be and they're planted in 2 inches of bark/compost over a clay substrate.

Potted plants are also an option. Regarding the sand, I'm not sure if it provides a lot of drainage. I've read conflicting reports. When dealing with large areas of land as you are, my choice would be to get plants suited to the soil rather than changing the soil to suit plants and wherever you want plants that don't like the soil create a raised garden or place pots in that location.

DoGooder

This message was edited Jun 17, 2012 2:13 PM

Thanks,
The thing is a lot of fill (top soil and/or compost) has to be delivered. The area needs 1' deep in an area 50' X 20'. So, if improvements are gonna happen now is the time...

physeek, am I to understand that the city is paying for the fill? In that case would they be deciding what kind of fill to add or are they allowing you to decide? In any case, 1 foot of topsoil & compost over a clay substrate is fine for shallow rooted plants but most shrubs and larger plants will eventually grow roots into the clay (if they can) so it would be best to get deep-rooted plants that tolerate or thrive in clay.

DoGooder

This is 2 separate areas (each aprox. 4'x6' ,or 5'x8') that have been bucket crane dredged and back filled with all clay. The clay is not part of the ground structure right there, but put there as fill from the salt water canal.

I have started to dig it out and spread the shovels on the top to dry out, and later was going to smash them into small granules and mix into the sandy soil. I'm going to get a landscapers estimate for the remaining fill job and question the clay areas etc. before continuing with this labor. Maybe a machine will be needed anyway. The large amount of topsoil/compost (est. might require 30 yards) that will need to be delivered and labor is my cost.

physeek, if I was you I would wheelbarrow the clay to a place where I don't intend to plant anything, haul it away, or use it to make garden sculpture. I tried using clay cat litter as a soil amendment and I poured water over it to remove the dust and after a few seconds it turned into clay so heavy I could not pick up the mixing pot. I couldn't even scoop it into another mixing pot because it was so thick trying to scoop it was like banging against a wall. That was my first experience mixing clay with planting media and I realized why so many gardeners dread clay.

Clay has a way of taking over the soil. I've read of people mixing clay with organic matter every year for decades and it had no effect at loosening the clay. I ended up throwing out most of the clay mix, but I did use a small part of it to develop a successful begonia planting mix using the following formula:

(approximate)
75% perlite (washed to remove dust)
15% bark dust (mulch)
10% clay cat litter

The wax begonias like this mix (see attached picture). I put extra begonias from planting trays in a box and I keep thinning out the begonias but they grow fast and take over the extra space. So clay in small amounts like 10% is fine, but even with 10% clay the media has a heavy consistency and never seems to dry but it's porous enough to drain water well enough for the begonias to be healthy. I'm only a beginner gardener but my experience has taught me to use clay in small amounts with extreme caution and never try to amend large tracts of clay soil. - DoGooder