Hi. I just moved into a rental property in South Delta, and the landlord has given the go-ahead to convert the totally suburban backyard into a garden. When we pulled up sod for a bed near the cedar hedge, we discovered one area with black plastic beneath the sod. When we pulled up the black plastic, it revealed an area of fairly large root network, presumably belonging to the hedge. These roots are up to 1.5 inches in diameter, and the soil below is fairly dense with clay. The plan was to till the soil and then add up to a foot of very good new top soil for bedding plants, perennials, etc... What do I do to the roots? My inclination is to go in with a hatchet and remove as many as I can. This area is approximately 24 inches from the base of the hedge - the trunks of the cedars. If I hack at the roots, is this going to kill part of the hedge? Is it best to just replace the black plastic? I'd really appreciate some advice before I take the next step.
If bringing in topsoil anyway skip the hacking and tilling and just pile up topsoil to plant in. Use rocks, concrete or other barrier to retain topsoil and provide benches to sit on while working. Will need bright sun exposure for most vegetables, hedge near vegetables can be good for cutting cold winds but if tall will also cast a shadow. George Schenk's book The Complete Shade Gardener has a chapter on vegetable gardening in less that full sun.
The cedar roots, if not covered with some kind of barrier, will grow into any topsoil placed there. Not sure how that will affect your plantings in the topsoil in regards to drainage and root depth.
You do have an interesting situation here. Normally one is told not to put plastic or even raised beds onto roots for the good of the trees... but they're fine with the plastic in place, obviously. And as Chimera says, without the plastic, you're looking at serious root competition from the cedars for anything you plant there. Sooo..... I'd be inclined to quietly leave the plastic in place, haul in the dirt, and plant like mad. The plastic will affect the growing conditions of the new plantings, and it won't be the place for trees or large shrubs, but that's probably not what you have in mind anyway. And since the roots of your plants can't range deep into the soil in search of moisture, they may need more watering attention in summer as well as attention to drainage in winter. If you have a bit of a slope there you're in fine shape.
Thanks for your insights, everyone. The garden is a fairly large plot that faces due south over pasture land, but is hedged by cedars on one side and a garage on the other. The cedar hedge seems incredibly well established, and it looks like the neighbour on the other side has been more fastidious over the last several years. I had hoped to trim the hedge back a few inches and plant tall plants as a background to distract from the hedge... Sunflowers, tall grasses... Will cutting the roots harm the hedge? Is that too great a risk to venture? Thanks again.
Cutting the cedar roots will probably not harm the hedge much, but I think the point is that there is no point in doing it. They will grow back. And if the roots have basically figured out that there is limited nutrition to be had in that area, then the little roots that really do the most feeding and sucking up of water are growing either on the neighbour's side or beyond the limits of the plastic on your side. If you cut the roots where you wish to plant, then the cut ends of the roots will sprout rootlets galore, and THEN you will have major root competition within a year or two. Even if you just pull up the plastic and give them good soil and water, they will sprout rootlets. Your ability to grow anything in this area successfully will be compromised if you pull up that plastic whether you also cut the roots or not. I will add that it sounds as though the neighbour likes the hedge, and the fact that it belongs to either the neighbour or your landlord - and not to you - should be factored in here. Cutting the roots wouldn't be likely the hurt the hedge, but before you take the chance you should price out the cost of replacing it.
I agree. I think I'll simply put down new plastic over that one strip and see what I can do with the new soil. Thanks - it's quite useful information.
Hi Mark - I'm just wondering about drainage. With the plastic in place, what were you planning to put down on top of the plastic so the soil can drain? If it rains hard, I'm wondering if this will partly wash out your new bed. I'm suggesting you could use a garden box made from a piece of plywood which would be open on the bottom. You could easily make one yourself by taking a piece of standard plywood and ripping it in half (lengthwise cut), then cut 2' off the two ends. If you reinforce the ends with some 1"X2" you can nail or screw it together, then use some metal brackets to help support it. I've been using boxes like these for eight years now, and they work well. Eventually they'll rot, but you'll get lots of good use out of them before they do, and it will take years since they've got no bottom. You can paint or stain the outside if you want. You can use the bottom of the box to put rocks, bits of wood, unfinished compost or anything you might compost but will take a long time to break down. Put your topsoil, finished compost etc on the top and you're ready to plant. You can also make a chicken wire top for it if you've got deer problems there. Also, you can take the whole thing apart and move it if needed.
No, you don't want to do that. It blocks the exchange of gases and causes water runoff and drainage problems in other areas. The plastic that was there, caused surface rooting to be somewhat different. Some root pruning with a sharp tool could be useful. Is this a tall cedar tree hedge? Or is it a sheared cedar hedge? How big is the hedge? That's important regarding how much root to cut.
Hi MD Vaden: in regard to your first sentence - would the drainage problems and gas exchange blockages be because of piling stuff onto the plastic - the combination of the two? I would've thought the plastic would block gas exchanges all by itself, but it doesn't sound like it has. I went to your website, and there's loads of great information there. Where I garden is pretty much all rock, so there's a big difference between here and what Mark is dealing with. I'm guessing that's why my system works here. Thanks for sharing your time and expertise!
Soil is intricate, but just one aspect is roots. Roots use oxygen and emit carbon dioxide, unlike the leaves which are mostly in reverse. Its not as severe as us duct taping a plastic bag over our head, but its a portion of that concept. Plastic, in most cases, won't stop weeds - they just germinate on top. You've seen tiny trees grow in dirty, moist rain gutters before, I'd guess.
You find a concentration of visible roots when you pull up plastic because they need air and have grown right against the plastic trying to get more of it.
