vendredi 28 mars 2008

Soil conditions and grass seed 101

Soil -- pH 7 and sandy

Searching the Internet yesterday, I found some very helpful ideas on Bachman's Floral, Home & Garden site from Minneapolis/St. Paul. To see what kind of soil you have, get a quart bottle (liter in my case, but that is just fine in the garden terms of exactness), fill it half-full with soil dug up from your garden, fill the rest with water, add a teaspoon of Calgon "if you have it" (I bought some... not that I needed it in the end since it is for clay soil testing), and then
Put the lid on the jar and shake it energetically until everything is swirling around [gardener's can't stop being descriptive even when they are trying to be scientific]. Then set it aside and let it settle until the water clears. The sand particles are the heaviest and they will settle to the bottom within a few minutes. Within an hour or two, the silt will have formed the next layer. The fine clay particles will finally settle, but it may take a day or so. Organic matter may remain floating around on the top. Looking at the layers, you can now see, comparatively, how much sand, silt and clay make up your soil.
If the clay makes up most of the content, then you have heavy clay soil. If the elements are present in equal parts, you have medium, loamy soil, and if there is mostly sand, you can basically forget looking for clay, which is what I did after 10 minutes when most of the soil had settled into sand particles with some 30% silt. You can see the silt in the photo; it's the darker layer on top of the rest. Don't see much organic matter. How surprising.

For those of you interested, I will add a link for the soil drainage test, which you can read by clicking here.

So, what this means is that of the three conditions that are hostile to grass, but make moss very happy -- shade, clay soil, and lots of moisture -- clay is not my problem, which means that soil compaction is not either as far as grass is concerned. I dug my sample to nearly 10" deep, which is fine for grass roots to develop, and from having turned the soil over back in 2003, I know it is similar deeper down. Furthermore, other plants grow very well, so I am not as troubled by the deep soil conditions. Shade and moisture are my culprits. We can add two other conditions, low soil pH and low nutrient soil. Of these two, only low nutrient levels in the soil is a likely factor.

This leaves me with a few things to do.

Last year we pruned the two Linden trees, which we do every 2-3 years. They are very densely branched and large-leaved trees, creating two areas of solid shade that rotate slowly with the sun. I had cut out some of the lower main branches, but I can't go farther because being ornamental trees, they have been deliberately pruned to maintain a medium height over the years, and it is impossible to remove any of the lowest branches remaining without making them ridiculous. Consequently, I have to live with the shade.

Next, I looked more carefully at where the moss does not create as terrible a problem, and it is where I had put down the grass seed blend for shady areas. It is a mix of English ryegrass and red fescues, with the addition of paturin des bois, in the following ratios:
  • 35% English ryegrass, Lolium perenne
  • 15% Red fescue "gazonnante", "Chewings Red", "Chewings Fescue", Festuca rubra commutata
  • 40% Red fescue "traçante", "Red Fescue", "Strong Creeping", Festuca rubra rubra
  • 10% Paturin des Bois, Wood Bluegrass or Wood Meadow-grass, Poa nemoralis
The rustic blend I used on the second terrace with some success is similar, but lacking the Wood Meadow-grass and heavier on the ryegrass:
  • 55% English ryegrass
  • 40% Red fescue "traçante"
  • 5% Red fescue "gazonnante"
Is it enough just to read the product names on the box that tell you for what conditions the mix is good? My online reading tells me that it is. The commercial suppliers do the work for you, but if you are anything like I am, then you want to know everything so that when it fails, you have a clue about what happened.

Each type of grass has its preferences, like any other plant, for soil type, drainage, exposition, and climate. In the case of grass, you can add use because some grass types tolerate being walked around on better than others.

In the most general terms, grass is distinguished into two groups, the coarse and the fine grasses, with perennial ryegrass, or English ryegrass, and the Wood Meadow-grass in the former category, and the fescues in the second.

This grass is only there because of its ability to establish quickly while the slower germinating grasses, like the blues and the fescues, establish themselves. It doesn't last long, especially where it is very hot or cold, but it offers the following qualities and disadvantages, depending on your point of view:
  • highly resistant to piétinement, your word of the day, a lovely word for "being walked about on"
  • highly competitive for the first season or two, and then gives way to other grasses, like the red fescues.
  • grows rapidly and abundantly, necessitating frequent mowing, up to twice a week
  • demands cool, fertile soils with regular watering
  • does not like drought conditions and heat
  • finds its usefulness in large green spaces and sports fields, in a recommended dose of about 30% according to one source
The Fescues
These are considered by the same source as being especially interesting in nearly every region of France, which is good for me, but they are good in many parts of the States, too. They are, if you believe him, a sort of wonder grass:
  • form a lawn fine, dense and compact, which we love and prize
  • adapt to all soils and climates except the Midi and the Mediterranean (who cares! I am not there!)
  • good grass for lawns and sports fields, large green areas, banks and ski slopes (under the snow)
  • highly resistant to drought conditions, too much water and cold (my dream grass)
  • tolerate shade well
  • tolerate frequent and short mowing
  • "delicate" establishment, rather slow, and grows rather little (fine by me)
  • medium resistance to piétinement (off that lawn, kids!) and susceptible to disease
  • good perennial grass (long lasting)
Between the two forms of fescue, the Chewings Fescue and the Creeping Strong, there are opposite qualities that suggest the need to use them in some proportion of mix, according to the conditions. The Creeping Strong produces rhizomes, which help it to reproduce quickly and, thus, rapidly fill bare areas, but it is a coarser grass that gives a less dense lawn. Nonetheless, while it also weathers the winter well, it doesn't turn straw-colored like the Chewings Fescue, and because of the horizontally creeping nature of its root development, it is less demanding about soil type, but this also explains its sensitivity to piétinement. It also has a nasty clumping habit, which flies in the face of my perfectly even emerald carpet mania. This depresses me about the shade mix, where it is 40% of the seed, but green grass is better than green moss, at least in this lawn.

The Wood Meadow-grass
For its part, like the ryegrasses, it is a coarse grass, and of the three types of Poas -- pratensis (meadow), nemoralis (wood) and trivialis (common) -- it is the least used. Its chief interest is its resistance to shade. It is a short, light green, fine-bladed grass, that when present in a mix makes a grass that contrasts fairly starkly with the fescue and ryegrass blends that do not contain it. I know because I used the shade mix with it in a shady corner, and you could really tell where it stopped and the rest began, although it is less obvious now that the rest of the grass has started to thin out. It also doesn't like being mowed, but that's fine because it's not the dominant grass in the mix. And, above all, sow before the trees leaf-out to give it some light by which to germinate.

This explains my rush right now... the Linden trees are getting ready to burst into leaf, and once the buds open, you can practically see those large leaves grow in size.

So, what is my conclusion? That I bought a big bag of the wrong grass seed! Oh well, I can use it to overseed the second terrace and the long-neglected lawn down by the pool, and I'll go buy more grass seed for shady areas.

The question that remains is, with my sandy soil conditions and lack of nutrients in the soil, to rototill or not to rototill?

I can try, at least for this year, using the power thatcher, and then topdressing with organic material and topsoil and see if that produces acceptable results.

Rototilling the whole thing under and then working 4" of mixed organic material and topsoil across the entire surface into the soil, fertilizing and reseeding would probably be my surest option.
Valuable Words of Wisdom
I include the following from Cornell's "Amending Sandy , Gravelly or Clayey Soils to Grow a Lawn". I know now what they are worth, having gone through what I have these last 5 seasons, and you will, too, once I tell that whole story.
Extreme care is needed when buying topsoil. There are no regulations about the actual content of topsoil [not in France either, I can assure you], hence many different materials are called topsoil in the landscape and building trades. Some "topsoils" have been found to contain excessive amounts of stones, clay, sand, wood, demolition debris, or other undesirable matter [we had it all, and then some, but when the adjunct mayor happened by when we were having it delivered -- 13 meters cubed of it -- he said, "Now that's nice topsoil!" Man doesn't know topsoil.]. Always inspect topsoil before you buy it. Insist on an accurate sample if you buy topsoil from someone who will deliver it for you. If a slightly moist sample of the topsoil seems adequate to make clay pots from, it is probably too high in clay. If it is extremely gritty, then it contains too much sand. Stones and other large debris should be apparent by visual inspection. If possible, be on-site when the topsoil is delivered, so that a load can be rejected if it is not the same as the sample material you previously inspected.


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