Raising the soil in large container beds

14 years ago

Hi,

I have Hayward fuzzy kiwi vines planted in 3 large planters. They are trained to a pergola above them. I built the planters and filled them up with a mix of peat and Gardener's Gold Premium Compost. The planters have no bottoms, so they connect directly to the earth below. Because of the 'Fixed' nature of the containers and the kiwi vines, repotting is not really an option.

The problem is that the base trunks of the kiwis are sinking as the organic material in the containers shrinks. So the base trunks now sit in the containers about 5 inches lower than when I planted them 1.5 years ago. I'm afraid that if I do nothing, they'll just keep sinking as the organic material gets used up (or will the vines atop the Pergola hold the plants up and prevent them from sinking more??). If I add more organic material now, it might cause the trunks to rot, but I was thinking I could surrounded the base of the trunks with a rigid plastic barrier to keep compost off them directly, and put compost around that barrier and fill the container back up to the top. I'm thinking it might work to keep them from sinking more.

Any other suggestions? Photo link is from 2008 summer (the vines are much larger after 2009 summer). The kiwi vines are in the 3 tallest container sections which are about 30 inches high. Thanks for any ideas!

Robert

[IMG]http://i569.photobucket.com/albums/ss138/7molly4/2008_09150009.jpg[/IMG]

Here is a link that might be useful:

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Comments (8)

justaguy2
14 years ago
you can safely replace soil volume that has been lost to weathering/biological breakdown in this situation.
blueberrypancakes
Original Author
14 years ago
Hi justaguy. Do you mean just add new soil to the top, even if it sits around the trunk of the kiwi vine? Wouldn't that cause trunk rot? Should I but a barrier around the trunk first, to keep the new soil from contacting the trunk? Thank you very much.
Robert
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The soil above should come in at a pH in the neighborhood of about 5.2 - 5.5 before liming. Gypsum has no, or nearly no effect on soil pH, and tomatoes growing on prefer the soil in the 5.2 - 5.8 range, so it hardly gets any better. When you factor in the tendency for soils to climb in pH as they age, you should be just right. I never worry about soil pH in container culture. If a hobbyist tells me, "I maintain a soil pH of ______", or even give a narrow range pH and claim to be able to maintain it, I immediately suspect the veracity of the claim, even if I don't challenge it. As hobbyists, we can generally point the pH in the right direction, and that's about as good as it gets. Trying to maintain pH at any predictable potential is an exercise in futility because of the number of factors that vary by the hour and have large sway on container soil pH. Al
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The physics of soil hydrology are radically different between containers and gardens or raised beds. Raised beds have a never-ending wick to pull water from soils, or water flows laterally with the help of gravity to keep the soil in a permanently unsaturated state. In containers, downward water flow stops when it hits the container bottom and when soils are comprised of fine particles with tiny air spaces, water perches in a column at the bottom of the container or above coarse drainage material. (More on that in the link below.) Soils don't technically fatigue in containers like they do in beds or gardens. If we do not replace organic matter in our garden soils, they fatigue & become less favorable culturally. In containers, we grow in a near all-organic mixes (most often). They don't fatigue like mineral soils, but they do fail structurally. Large particles become smaller with age. They hold more water and less air. It's possible that a soil can be fine for a mature planting with roots fully colonizing the container, but a death sentence for anything over-potted. You should choose a container soil that will retain air for the expected life of the planting. When it stops retaining air, many will tell you that they rejuvenate it with the addition of "fresh ingredients". There may be some temporary truth to this, but imagine this: Compare a collapsed soil to pudding (made with water). They both hold too much water and too little air for plants to grow with vitality. Can we amend the pudding with an ingredient, the primary function of which is to increase aeration (perlite) to make the pudding a desirable medium? Why then, would we use things like collapsed soils or compost, amended with perlite & expect good results? So - soil fatigue in in situ soils can be corrected with the addition of organic matter. Soil collapse in containers is a structural issue & needs addressing via a different avenue. The best way is to replace the soil with a mix that guarantees good aeration and insures structural stability. I would turn the soil in your barrels into the raised beds fairly regularly, where they will be a welcome & wonderful addition, & start with a fresh soil in the barrels. Al Here is a link that might be useful: More info
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If your native soil is truly sandy it might work OK, but I've found that although my native soil works great in the garden, it is a complete disaster once I use it in any amount in a pot or raised bed (or the compost pile for that matter). This is due to the clay content. Now I make my own potting soil with volcanic scoria (cinder) mixed roughly 60/40 with some fluffy organic material such as compost. It works really well for me and is basically free, since I make the compost myself, and collect the scoria from a nearby volcanic hillside. Without that much compost you could use peat or some inexpensive compost available by the truckload. I think you'll have better results if you avoid anything loosely called "topsoil" since this can often be bare mineral soil with no organic matter, lots of caliche, and a high clay content.
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justaguy2
14 years ago
hmmm, perhaps I misspoke. Are you saying the soil has sunk, but the entire vine has sunk with the soil? In other words are you saying the trunk remains buried to the same point it was when first planted?

What I was saying above is that if the soil has lowered and thus exposed more of the trunk/roots that you can replace that lost volume.

I am not familiar enough with kiwi vines to say if it's safe to add soil to the point where it covers the vine higher up the trunk than it was when first planted.
tapla (mid-Michigan, USDA z5b-6a)
14 years ago
The vines in the picture are quite young, so I don't think there will be a major issue with adding soil, but here is what will happen:
New roots will form above the old roots, because essentially you'll be ground-layering the plant. As the plant recognizes the highest roots as the strongest energy sinks, it will begin to 'ignore' the lower roots, which will die. There may be some minor sacrifice in growth that you will not be able to detect because it's 'potential' growth. IOW, it might slow your plant's development a little, but you won't really know it.

My suggestion is to replace the needed soil with a mix that has a very high mineral content to prevent the rapid collapse you would expect in soils with such a high organic content. Search the container forum for info on soils like the "gritty mix" for more detailed soil info.

Al
blueberrypancakes
Original Author
14 years ago
Thanks for the advice justaguy and Al. The picture is about a year and half old, so the vines have had 2 summers to grow--the trunks are about an inch and a half in diameter at the base now (they sunk with the soil, so the roots aren't exposed). Al, do you think that they will still make the new roots above the old ones at this size?

I'll use the gritty mix for filler going forward! Wish I would've done that from the beginning!

Thanks,
Robert
tapla (mid-Michigan, USDA z5b-6a)
14 years ago
Yes, new roots will form above the old, if you're burying part of the stem that is exposed and has no roots. You often see the results of unintentional ground-layering when nurseries bump their unsold material to larger containers & bury the old trunks. New roots form above the old, and often, the old roots are declining while the new roots are 'taking over'. I have several trees (for bonsai) that I am intentionally shortening (from the bottom up) by doing what you're about to do. The only difference is that I girdled the trunk completely, removing a ring of bark = to 1-1/2X the diameter of the trunk to facilitate the rapid formation of roots exactly where I want them to grow. I'll cut off the old rootage entirely when I repot in the spring & wind up with a bonsai with its lowest branches much closer to the soil than when the tree was on the old roots. You'd be really amazed if you knew some of the tricks experienced bonsai practitioners use to manipulate their plants. ;o)

Al
blueberrypancakes
Original Author
14 years ago
Thanks Al! I will proceed without fear of killing the kiwis... using the gritty mix to top off the planters now and in the future. I think I'll stay away from trunk girdling though.
Best regards,
Robert
tapla (mid-Michigan, USDA z5b-6a)
14 years ago
Oh ye of little faith ..... :+)

Al

Raising the soil in large container beds

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justaguy2

blueberrypancakes
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tapla (mid-Michigan, USDA z5b-6a)

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Raising the soil in large container beds

Comments (8)

justaguy2

blueberrypancakesOriginal Author

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justaguy2

tapla (mid-Michigan, USDA z5b-6a)

blueberrypancakesOriginal Author

tapla (mid-Michigan, USDA z5b-6a)

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