Soil Amendments vs. Importing

Asked June 26, 2020, 7:03 PM EDT

Hello, we are building a new home in Minneapolis on a very small lot. The lot is 28 feet wide and we will have side yards that are 8 feet and 5 feet wide. We had the soil the contractor imported tested by the UofM (attached), however I don't really know what I am supposed to do with the results of the test report. I am hoping you could make a recommendations for soil amendment types/quantities.

Attachment 3601 = Soil Test for Most of the Site
Attachment 3602 = Soil Test for the area between our house and the neighbors house. It acts like it is clay. Water pools, it cracks when it dries out. There is roughly 10 feet between our house and the neighbors house.

1. Organic Matter is very low: Could we incorporate compost into the soil to raise the organic matter, if so how much and to what depth should it be tilled in? For example, could we import an inch or two (or six) of compost over the whole site a till it in? MnDOT Specs for topsoil say a range from 3%-15%. Is this what you would recommend?
2. Should/can anything be done about the pH? Comparing it to the pH range that MnDOT requires (6.1 - 7.5) in their topsoil specification this looks high.
3. Do these soil reports tell us anything else about our soils? It doesn't look like it indicates soil texture, so it doesn't designate if the one area is clay or not. Is there anything else you would recommend we do?
4. Would we be better off removing and re-importing different topsoil?

Much Appreciate, Jena

Hennepin County Minnesota

3 Responses

Welcome to the neighborhood ! It is a great location and not called the garden neighborhood by accident. By coincidence I live a few blocks from your new home and have gardened here for many years. A pH of 8 is high but most plants will grow. Azaleas, rhododendron, won’t do well. Most of Longfellow is heavy clay. Compost is going to be your best friend. Extension recommends up to 30% compost. It does break down overtime and has to be replenished. With a lawn leaving the clippings on the lawn is helpful. I would apply 6 inches of compost or wood chips and wait a year for it to break down. It’s hard to wait but your preparation and patience now will have a huge impact on your satisfaction later. I am not sure replacing the top soil is going to be practical, it is very difficult to find a reliable source of weed free, rich top soil.

The Longfellow Garden Club is a fun resource and they have a Facebook page.
Best wishes on your new home.




Hello Neighbor! That address is actually for our old house, and we did have VERY heavy clay there. The new house is two blocks away, at the corner of 36th Street and 42nd Ave on the South-East corner of Sanford Middle School. Due to construction, none of the existing soil is remaining. Everything that is here now was imported by the contractor.

When you say "wait a year", does that mean before we plant anything? Unfortunately the city is requiring us to have the site fully planted before our permit is closed. So we need to have everything be either turf or plants. We also need to plant 4 trees on the site per city requirements. Because we cannot wait, is it okay to incorporate the compost and plant this year? OR Would it be best to seed with a cover crop, and then plant and seed turf next year?

Thanks,
Jena


Hello, Good morning. Your new house is on the same block as another garden club board member. Hers is the small house with the big garden in front.

It would be best to plant grass next year. Add a several inches of compost as much as 30 % so to 6 inches of fill add 3-4 inches compost. Plant a nitrogen fixing cover crop. See how the areas of the lot respond. Compaction from the construction is highly likely. If there are areas that pond after a rain consider planting a companion busting prairie plant. The most extreme renovation I have seen in the neighborhood was on 32nd and 37 th. ( blue stucco) where they planted their entire yard with cup flowers ( they get 8 ft tall), let them grow for 2 years, cut them down, tilled them in and planted grass. Prairie natives can bust up compacted soils to 3 ft. Lead plants are one of the best. But that is an extreme “make over”.Red clover is to my eye the prettiest cover crop. I have used annual rye as a cover crop and it makes a good green manure too. If you have an area that is a problem asking for plants on Nextdoor will probably get you lots. Fall or spring is the best time to plant or sod a lawn so waiting if you can would be best. Annual rye would be ready to till in afternoon 30 days so you could plant it and install a lawn in the fall. Being an annual it will die over the winter.
Here are some resources about installing lawns and restoring the soil after construction.
I use a Pseudonym but hope to see you if you check out Longfellow Garden Club. I am on the board.