Monday, October 31, 2005

Of sowthistle and saltgrass

I've started to notice patterns in the vegetation of our yard. If you don't know the Arcola area, you might want to know some background. The area in general is a glacial lake bed, with mostly clay soil as I recall, and high salinity in the lowest areas. Our yard (pictures here and here) is right on the margin of the old "brick ponds," where there used to be a brick factory about a century ago. I don't know what the areal extent of that operation was, so who knows - maybe the soil in our yard was disturbed back then. Presently it's mostly lawn with some unimaginative hedges and tree rows along the edges. Last year I didn't do much to it besides planting some veggies in the square of bare (well, weedy) soil and mowing the rest. This year I've noticed three main types of growth in the lawn: the thin scraggly stuff in the shade north of the house and under the tree rows; a fairly healthy patch on sunny level ground just south of the house; and a weedy area on the very sunny slope south toward the brick ponds. The scraggly stuff doesn't cut neatly with my push-powered reel-type lawn mower, but as noted in my previous post, I've come up with a plan to greatly reduce the area of such grass. Now it's just the weedy area on the sunny slope that's bothering me. Why is it so thick with sowthistle? I asked our neighbour, and she said it's because of all the sowthistles blooming in the long grass around the brick ponds and spreading seed. Maybe partly, but there's a definite area where they are almost choking out the lawn, and in other areas I don't notice sowthistles at all. I got thinking it must be something in the soil. I guessed salinity might be an issue, and the vegetation seems to confirm that: I found desert saltgrass (Distichlis stricta) growing through the same area as the sowthistle, as well as some kochia patches nearby. It would make sense that there could be some salinity on this slope above the brick ponds, due to evaporation and capillary action drawing water up from the ponds through the soil and leaving its salts at the surface.

Now what? I suppose the most common approach would be to try to kill the sowthistle with a herbicide, but that won't fix the salinity. Irrigation might, but if I'm going to water my landscape, I'll water the garden part. No, I'll have to look for something more subtle. I am thinking maybe if I overseed some other salt-tolerant plants, like Nuttall's salt-meadow grass (Puccinellia nuttalliana), I can give the sowthistle some stiffer competition. I'm also wondering if I should look at some alternative to lawn there, like some low shrubs to shade the soil more to reduce the evaporation. However, that's one area where I do like to have a mown lawn, just as a deterrent to any wandering creatures that might come in from the "wilds" of the brick ponds. I'm still pondering.

Thanks to Wayne for a post that prodded me to write about all this.


Wayne said...

Thanks, Laura, for notifying me about this!

We also have a lot of sowthistles and wild lettuce. The latter crop up in the spring and even after two years of pulling them up as they're flowering, they still keep coming up.

Sowthistles, and none of our species are native, are actually recommended as companion plants for gardens - corn, tomatoes, and onions. I haven't found why they're valuable in this way but I assume it's a nasturtium effect - they draw away insects that would otherwise attack the crop plants.

The Puccinellia nuttalliana sounds like a great grass to plant. USDA Plants gives the common name as alkaligrass. Is your soil alkaline, as opposed to or in addition to saline?

Laura said...

Not having done any testing, I can't say for sure, but my understanding is that true alkali soils are rare if not absent in Saskatchewan. Most farmers call the white patches where nothing grows "alkali," but saline is more accurate, indicating high concentrations of soluble salts (usually sodium sulphate, magnesium sulphate, and calcium sulphate). Because they are water soluble, these salts move upward through the soil where evaporation exceeds precipitation. Such conditions are very common in our prairies, and if groundwater sustains the condition through much of the year, for instance around a slough, the salts can build up at the soil surface.