Black Walnut Resistant Grass

(Question)

Hi,

I have a shady back yard that is pestered by a Black Walnut tree on my neighbors yard. I am looking for suggestions of what grass I could grow that would survive albeit some additional tlc.

I read this response to another writer who has a mildew issue
https://www.torontomastergardeners.ca/askagardener/shady-lawn-has-mildew/

Also this government guide to resistant plants
https://www.omafra.gov.on.ca/english/crops/facts/info_walnut_toxicity.htm

There is plenty of great advice on here but still allot to take in for a beginner like me. Wondering if someone has some advice on what my best options would be.

Thank you in advance!

(Answer)

There is certainly no dearth of information out there on how to garden under Black Walnut trees, so we will focus here on what you want to do: establishing a lawn under the shade of a Juglans nigra.

First of all, is there a possibility of persuading your neighbour to let an arborist prune their Black Walnut tree to open up the canopy? Even shade-tolerant species of turfgrass need a minimum of 4 hours of sun every day. More sunlight can be let in after the lower branches are removed (limbing up) and upper branches thinned out. That goes a long way to help your grass stay healthy.

Of the two turfgrass listed by OMAFRA as juglone tolerant, only the Fescue (Festuca sp.) is also shade tolerant. You may already be familiar with Red Fescue (Festuca rubra) as a fine-textured grass that is the preferred choice for shady locations. The University of Virginia State Extension further specifies that the Tall Fescue (Festuca arundinacea) is juglone tolerant. Unfortunately Tall Fescue is coarser in texture, less shade tolerant, and not reliably hardy in our climate. Your best best may be a mixture of several different types of Fescue.

You may also want to consider these alternative ‘weedy’, shade-tolerant grasses that are identified as juglone tolerant by OMAFRA: Redtop grass (Agrostis gigantea), Orchardgrass (Dactylis glomerata), and White Clover (Trifolium repens).

Here are a few pointers on how take care of a shady lawn. Remove all plant debris from the lawn promptly (and, needless to say, especially anything from the Black Walnut tree) to prevent smothering of the lawn. Mow less frequently, and set the mowing height to 0.5 to 1 inch higher than normal. Remove the clippings regularly to avoid thatch buildup; this is important because grass growing in shade need a larger surface area to take advantage of the limited sun, and everything that potentially reduce light reaching the leaf blades, like thatch, should be removed. Grass growing in shade also needs only one-half to two-thirds as much nitrogen as grass growing in full sun. Take care not to overfertilize, and avoid fertilizers with a high number in nitrogen (N). In Fall, use a high potassium (K) autumn lawn feed just prior to leaf fall to strengthen the root system. If you wish to fertilize in Spring, then do it early, about one month before trees begin to leaf, and use only half the rate of spring/summer lawn feed applied to turf in full sun. Lawns in shade also need less water than lawns in full-sun. Aim to water infrequently but deeply, in the morning rather than afternoon so that the lawn has a chance to dry. Minimize stress to the grass like foot traffic (e.g. install stepping stones) and herbicide use.

If you want to go one step further, amend the soil with organic matter like compost regularly, which aids drainage and therefore the leaching away of juglone toxin.

Good luck!