Weed Fabric and Sand Beds

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Anonymous
Title: Guest
Weed Fabric and Sand Beds

This thread was split off in the second page of a topic that began here:
http://nargs.org/smf/index.php?topic=698.0
--- Moderator

Tim wrote:

It may have been wise to do it because worms and ants are steadily bringing up a lot of soil. I will probably do this next time.

I have found that the ants will just cut holes through landscape fabric. It is not horribly destructive, but they do bring up their diggings into the gravel. The holes made by the ants are small, however there can be a large number. The ants make trails from their nest under the fabric to distant locations, which means there is a hole where ever a little trail comes up from under the fabric.

Worms have been less of a problem. The worms largely avoid my dry gravel beds. Maybe the landscape fabric also has something to do with the lack of worms in my gravel beds. I don't know. Although, they do like to hang out just below the landscape fabric.

I really think it is a good idea to place a barrier down when gravel is spread over soil. If a gardener decides to rearrange a garden this will make life so much easier. It is an unbelievable amount of work to sieve gravel from soil. It is so much work a gardener is probably better off having the mix carted off and start over with fresh soil and clean gravel. A barrier eliminates a huge amount of work if one ever changes his/her mind.

It also helps prevent the gravel from sinking into the soil thereby eliminating the necessity to constantly add more gravel to the bed. Holes can be cut through the fabric for deeply rooted plants. This will allow the soil and gravel to mix, but it minimizes mixing as much as possible.

Even with gravel incorporated into soil, overly moist conditions can still be a problem. In many situations a raised bed should be considered first and the addition of gravel should be a secondary measure.

Of course you know all this, I am mentioning it for all the people that are still learning like myself.

James

Lori S.
Title: Moderator
Joined: 2009-10-27

James, the method of alpine gardening you seem to recommend - laying down landscape fabric with thin gravel overtop and cutting holes through it for planting, as described in your last message and here (http://nargs.org/smf/index.php?topic=810.msg12048#msg12048) is actually quite unusual.
The statement that readers here already "know all this" seems to imply that it is a commonly accepted method, though I don't find it to be that at all. 
If this is a method that you feel should be recommended to people who are still learning, it would be helpful to provide the "proof of the pudding" by backing it up with demonstrations that it is at least as successful as the more conventional methods of preparing alpine beds.

NARGS is, needless to say, a great resource for beginners to find information on the more conventional methods for preparing alpine beds.  A Rock Garden Handbook For Beginners, which was sent to new NARGS members back when I joined (and I presume still is?), is an excellent place to start.  And at the other end of the scale of endeavor, Stephanie Ferguson's treatise on rock garden construction from the Summer 2011 quarterly takes those basics of successful rock gardening to new heights - highly recommended reading!

Lori
Calgary, Alberta, Canada - Zone 3
-30 C to +30 C (rarely!); elevation ~1130m; annual precipitation ~40 cm

Mark McD
Title: Moderator
Joined: 2009-12-14

I can second Lori's response.  I am a staunch advocate of "NO landscape fabric", it has too many negative issues associated with its usage.  I have a friend that swears by landscape fabric, but over the 10 years where I have tried it, I realize I made a huge mistake, and have been slowly but surely ripping up the landscape fabric and disposing of it as I renovate areas; I shall NEVER use it again.  In my opinion, it is not at all conducive to rock gardening and drainage overall, and should be avoided.

Mark McDonough
Massachusetts, USA, near the New Hampshire border USDA Zone 5
antennaria at aol.com
 

Anonymous
Title: Guest

Lori wrote:

NARGS is, needless to say, a great resource for beginners to find information on the more conventional methods for preparing alpine beds.  A Rock Garden Handbook For Beginners, which was sent to new NARGS members back when I joined (and I presume still is?), is an excellent place to start. 

Dear Lori and Mark,

Please read the second paragraph of pp. 58 in the aforementioned publication.  I will include it below for the benefit of those who may not yet have this book.

"Gardening in Sand Beds" by Michael Slater

Weeds growing from seed are no problem at all.  If any do germinate and grow, they are incredibly easy to pull out.  The sand is delivered free of weed seeds, so weeding is much less of a burden than in any other garden I have.  As I mentioned above, weed seeds that blow into the beds only seem to germinate in the one spot where the surface of the sand stays damp for several days after a rainfall.  Rhizomatous grasses are another story.  They can be an incredible nuisance if they get into your sand bed.  But of course that is true of any "normal" rock garden.  An ounce of prevention is worth a pound of cure, so I recommend either an industrial strength weed barrier or careful edging with glyphosate herbicide.

Anonymous
Title: Guest

Lori wrote:

James, the method of alpine gardening you seem to recommend - laying down landscape fabric with thin gravel overtop and cutting holes through it for planting, as described in your last message and here (http://nargs.org/smf/index.php?topic=810.msg12048#msg12048) is actually quite unusual.

...

If this is a method that you feel should be recommended to people who are still learning, it would be helpful to provide the "proof of the pudding" by backing it up with demonstrations that it is at least as successful as the more conventional methods of preparing alpine beds.

I am sorry you do not find the example I gave in the photo I submitted in the above post to be satisfactory.  I planted this area with these species because I love hummingbirds and butterflies, not so much because they are traditional 'Rock Garden' plants.  The plants you see in the photo are Buddelia davidii, Penstemon cardinalis, and Penstemon eatonii.  Further along this same bed are species like Penstemon murrayanus, Liatris ligulistylis, and Silene regia.  Maybe you would have like the photo better if I had taken it when the flowers were blooming, instead of when I made that post in November.

Here's a post showing a plant that was grown surrounded by landscaping fabric (under the mulch).

http://nargs.org/smf/index.php?topic=24.msg12810#msg12810

Mark said this plant "... sure looks nice based on your photo." 

Here is another post http://nargs.org/smf/index.php?topic=274.msg12057;topicseen#msg12057.

Lori said "Very nice James" about my Geranium sanguineum.

Of course I did not mention either of these were surrounded by landscaping fabric when I posted the photos to the NARGS website.  I hope these examples provide you the necessary proof that plants can be grown well when using landscaping fabric.

Sincerely,

James

 

Lori S.
Title: Moderator
Joined: 2009-10-27

The Slater article talks about a "barrier" to keep grass rhizomes from invading from surrounding lawn, and then he expands later on the problem that rhizomatous grasses can pose when they invade, recommending an "industrial strength weed barrier or careful edging with glyphosate herbicide".  I see no mention of laying landscape fabric over the bed, placing a thin layer of gravel overtop, and cutting holes through it for planting.  

To restate it, your method of alpine bed construction is quite unusual.  If your results show success at growing alpines that is comparable with conventional methods of preparing alpine beds, that would carry weight.  Otherwise, I would be hesitant to recommend it to others, either to beginners, whom we certainly want to encourage with successful experiences, or to more experienced alpine gardeners.

Lori
Calgary, Alberta, Canada - Zone 3
-30 C to +30 C (rarely!); elevation ~1130m; annual precipitation ~40 cm

RickR
Title: Moderator
Joined: 2009-09-21

Dear James,

Lori is quite right.  The author you quote recommends using a weed barrier to prevent rhizomatous weeds from invading the sand bed, not to keep rhizomatous weeds from popping through the surface after they have colonized the sand bed.  Your method does not prevent weed root invasion.

For most rock gardeners who garden on the land (as opposed to pots and troughs), a rock garden is not an assemblage of stagnant plants.  By this I mean plants that are planted and grown, perhaps even to perfection, but the landscape and plants are unchanging: always X number of plants, Y number of species, placed in their designated spots only, and not allowed to naturalize.  There is nothing wrong with this type of gardening, but to claim that this is the norm by quoting the booklet A Rock Garden Handbook for Beginners in your support, is erroneous.

In fact, the norm is to have a diverse and dynamic garden, where plants can reseed and find their own "best" place in the landscape as they do in nature, thereby producing a more natural look and healthier garden to boot.  Your weed fabric method cannot achieve this, because the placement of the fabric does not allow for the natural, unplanned movement of plants.

Rick Rodich    zone 4a.    Annual precipitation ~24 inches
near Minneapolis, Minnesota, USA

Tim Ingram
Title: Member
Joined: 2011-04-27

Yes - I think Rick's point about a diverse and dynamic garden is a very valid one. This has always been my understanding of a garden; ie: you approach Nature as close as you can within the parameters set by your situation and interests. Essentially a garden is what satisfies you. Growers like Rick Lupp, who have pioneered sand bed gardening, do advocate fabric barriers, but these sand beds are relatively deep. The frustration of shallower barriers is that you no longer can actually cultivate the soil, ie: dig and plant! This is what gardening is for me, but then it is also a full time activity for me and for many others some way of controlling weeds must be important.

Alpine gardening really is a special case because these plants have such limited tolerance of normal garden conditions (to say the least!), but when you can get the conditions right with sand beds, crevice gardens, troughs, tufa and so on, then the plants repay you over and over. Experimentation must be the key, and considered advice from others.

Dr. Timothy John Ingram
Faversham, Kent, UK
I garden in a relatively hot and dry region (for the UK!), with an annual rainfall of around 25", winter lows of -10°C and summer highs of 30°C.
 

Anonymous
Title: Guest

It is really hard for me to respond when so many people are discussing so many different topics as if they were all same thing!

Lori keeps talking about growing alpines, which to me is not 'rock gardening' but rather one subset. She also keeps going back to the topic of weed fabric with a thin gravel mulch.  This topic is completely different than using weed fabric as a barrier to separate the native soil from a specific mix used in a special garden bed.  My original response to Tim was directed at using weed fabric to separate an imported medium from native soil.

Regarding using weed fabric under a gravel mulch for true alpines, no I would probably not do this.  Alpines are so tiny that using weed fabric would seem like using a 10 pound sledge to drive a penny nail.  Many are so miniature that I prefer to grow them in pots rather than in the open garden.  However, if I was constructing a special bed for alpines, I would not hesitate to put weed fabric under the sand, gravel, and stone to prevent mixing and invasion by rhizomatous weeds.

Rick seems to be following Lori's lead.  I will respond to Rick's comments below.

RickR wrote:

For most rock gardeners who garden on the land (as opposed to pots and troughs), a rock garden is not an assemblage of stagnant plants.  By this I mean plants that are planted and grown, perhaps even to perfection, but the landscape and plants are unchanging: always X number of plants, Y number of species, placed in their designated spots only, and not allowed to naturalize.   There is nothing wrong with this type of gardening, but to claim that this is the norm by quoting the booklet A Rock Garden Handbook for Beginners in your support, is erroneous.

Using weed fabric does not leave the garden unchanging.  It is true that seedlings are prevented from establishing.  However, competition from adult plants typically prevents new seedling establishment irregardless of whether weed fabric is utilized.  For rhizomatous perennials like Monardas and Coreopsis auriculata I must regularly cut away the weed fabric if I want them to expand.  Some plants like Penstemon cardinalis have a certain number of individuals that die for no apparent reason each year.  This gives me the opportunity to put a new plant in a vacant spot.  I am always moving stuff around in the garden.  The weed fabric does not stop me from changing the garden.  It is just a way to help me reduce maintenance.

Mark is commenting on his specific situation.  If sand, gravel, or some other special growing medium is not being used then the need for a barrier to separate it from the native soil has been eliminated.  A good mulching with leaves would be just as effective for reducing weeds in a woodland garden.  In fact, a mulching with leaves would be better because it would break down and feed the soil over time.  

Mark also may not need weed fabric because his garden is mature.  It is really only beneficial to use weed fabric under mulch when making a new bed.  The weed fabric smothers the weeds, weed seedlings, and grass (in the case of lawn).  Once the existing vegetation has died, holes can be cut in the fabric and plants can be planted.  Over time the weed seed bank is reduced and the plants fill in helping prevent weeds from establishing.  Once the garden has matured, then it may be desirable to ripe up the weed fabric.  It does take some effort to maintain the weed fabric.  This would not be worth the expenditure once the biggest threat from weeds has passed.  I would still maintain about a foot of fabric around a bed to help keep the rhizomatous grasses from creeping into it.

The need for weed fabric can be eliminated by turning the soil over, which smothers the weeds and seeds by burial.  I have done this many times and it is a lot of work.  Herbicide can be used to kill the existing vegetation (without turning the soil), however weed seedlings may still be a problem for a number of years using only this method.  

A surface weed barrier would also be unnecessary for a new garden bed made by laying weed free sand, gravel, growing mix, etc. over the existing soil.  It still is beneficial to use some sort of membrane to prevent the growing medium and native soil from mixing.  This membrane will also help prevent any weeds that are capable of pushing through the thick layer of growing medium from emerging.

Another reason I like weed fabric is because it helps keep my garden plants from growing into access corridors I use for maintenance or to cross a bed.  Rhizomatous plants, like many Monardas, will take over an entire area given the chance.  The weed fabric helps keep them in place.  They will still creep under the fabric and try to invade their neighbor's space, but it is easier to remove these few stems when the space where spread can occur is limited.

James

Weiser
Title: Member
Joined: 2009-12-04

  This discussion makes me leery about mentioning my use of PVC sheeting, laid on the soil surface, below a sloping raised bed. The bed is 2.5'deep grading down to to 1' deep. I grow a couple of dozen species of alpine and cacti in this 6' X 10' bed. The reason I placed the 50mil PVC sheeting down, was to keep tree roots from invading the bed.(It is within reach of a mature Silver Maple. This tree has spread it's fine feeder roots through out, my whole front yard. They surround and grow under this bed.) The lowest three inch layer of the bed is 3/4"> pumice stone for drainage the rest of the mix is 10% clay fines, 5% sphagnum, 20% 3/4"> pumice, 20%  2"> sharp basalt tailings and 45% 1/8"> DG (Decomposed Granite). In other words a lean, very course alpine mix.
  This bed has been in place of four years now and is thriving without the tree roots. The moisture  seeps through the mix, to the pumice layer, over the PVC and drains away at the edges. (Natural precipitation is supplemented by a micro-mister due to my dry climate)
  The key points, I wish to make, are that the feeder roots have not penetrated the barrier, there is excellent drainage, The plants can and do colonize the surface and the mix is deep enough to grow species not in need of very deep root runs.
  It works for me in this specific situation but I do not find the need to use this setup in the majority of cases. This bed and one set up as a moraine are the only two, I have, in which I use membranes/barriers.

Ok take your best shots. I can take it.  :-\  :-X  :'(

From the High Desert Steppe
of the Great Basin and the Eastern
Escarpment of the Sierra Nevada Range
Located in Reno/Sparks,NV  zone 6-7
http://www.flickr.com/photos/sierrarainshadow/
John P Weiser

Lori S.
Title: Moderator
Joined: 2009-10-27

John, there's obviously no need to feel "leery" about describing your method.  Your description makes it clear that it is very different from growing border plants under landscape fabric with a gravel mulch overtop, and likening it to rock gardening.  The substantial layer of coarse mix you describe clearly provides the required drainage for the alpines and cacti you are growing.  The use of a tree root barrier under it is clearly effective, and one that's used by various growers, as is well-documented in various articles in the quarterly and elsewhere.  I doubt there are any "shots" to be delivered.

Edited to add:  And it's clear, needless to say, that you didn't expect any either!  :)

Lori
Calgary, Alberta, Canada - Zone 3
-30 C to +30 C (rarely!); elevation ~1130m; annual precipitation ~40 cm

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