Planting for Moist Shade - Part 3

» Tim_Dutton - Japanese Iris

It's been weeks since I looked in at Suite101, Having just read this article Marge, I can tell you that all the Japanese Iris that I have in my bog garden are quite happy with wet feet all year round. They do not seem to flower well if too shady, so I have them planted in the sunniest spot, but still need to cut down a few shading trees that are due for removal. They grow in just about the wettest part of the garden, a solid clay pan in a bit of a dip, covered with a few inches of very rich compost. These irises have to be fed, so the compost needs topping up every year. I use well rotted horse manure. As we have our own horse, this is not a problem! Then the compost is covered with a couple of inches of wood chip mulch that I make. Over a 12 month period the mulch will all rot down, so the depth of soil keeps increasing over time.

This particular bog garden is pretty well sheltered, little wind, little frost, but gets a lot of rain in the winter. The irises thrive in these conditions.

Two other interesting plants that you may have come across for wet places, both of which seem to grow in shade or sun. You need space for both though.

The first is the marsh marigold, Caltha palustris. This will grow in standing water or just very wet soil. It has big bright green rounded leaves, large buttercup yellow flowers in spring, and spreads by sending out runners. It forms an ever expanding clump, but is easy to reduce in size. In my garden it is evergreen, but in colder climates is said to be deciduous or semi-evergreen.

The second is the Giant Hogweed, Heracleum mantegazzianum. This is a plant that you grow for a striking impact. It is a perennial, but flowers for the first time in its second year. I have a couple in flower at the moment (late spring here) which self seeded from plants grown two years ago (which then died - perhaps they are biennial), and they have large flat umbels of white flowers. Mine are about 18 inches to 2 feet across, but they are supposed to be able to get to 5 feet across!!! The flowers are so far above your head that you really need to plant them at the bottom of a slope and look at them from the top to see the flowers properly! My plants are only (?) around 10 feet tall at the moment. Two words of warning. They self seed very easily, so don't keep too many, and the plant contains a poison that can cause the skin to burn when exposed to sunlight. Try not to brush against them. Of course, mine just happen to be right next to the path. Bad planning.

I just love big perennials. I have some Gunnera tinctoria and Cynara cardunculus (cardoon) as well, both of which get pretty big.

-- posted by Tim_Dutton

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» Marge_Talt - Japanese Iris

Hi Tim,

We've missed you around here! I was beginning to wonder if you'd succombed to all the work of changing your stream course.

I am glad to hear you testify about the Japanese Iris. I wondered about the veracity of what I'd read, since I kept that lot in the pot in a saucer of water all winter and they seemed quite happy.

I also find interesting that you use manure on them as I had, once again, read that manure was fatal to them. Just goes to show that you cannot believe everything you read, even if written by reputable authors!!!

I knew they needed as much sun as they could get, so didn't even think about putting them in my new "bog" garden, which only gets dappled sun. I put the lot that's in a pot on the walk next to the drive - about the sunniest part of my garden. And, I'm seriously thinking about digging up the clump that's in my Circle Garden and putting them in a pot, too, so I can give them more sun. That garden gets shadier as time passes...as most do.

You are so lucky to have an unending supply of horse manure! What riches...I live in what used to be a "horsey" area - there are still a couple of places with them - but have not been able to get my hands on any manure...don't have anything to haul it in, for one thing. My NGP husband puts his foot down on hauling it in the car. Sigh...so close, yet so far away.

Caltha palustris I have seen photos of, but never seen "in the flesh". Once I see how the things I've put in that new garden fare, I will be able to tell if I have room to try this one.

Heracleum mantegazzianum I have also seen in pictures. That one I know I have no space for at the moment. It certainly is a monumental plant and I've mildly lusted for it as I muse through books that show it. I do love huge plants, too, but think one needs really deep borders for them to display well.

I've also read about its skin problem causing. How do you deal with cutting it back and all? Do gloves and long sleeves protect well enough? Do you compost the remains and if so, does rotting down get rid of the poison? If you are unlucky enough to brush it, can you go wash immediately or does the poison take effect instantly?

A net pal sent me Cardoon seeds and I'm trying my hand at growing this one. Lord only knows where I'll put it if I'm successful.

And, Gunnera....how I long for that one. Some day! I put Darmera peltata in the center of the new garden as a sort of substitute.

Your garden sounds quite marvelous. Got any photos to share??? If you do, and you can scan them, you can email me the scans and I'll be happy to put them up on a page so we can all enjoy your huge plants and bog garden. For that matter, I know Carol would be totally delighted to feature your garden on the Virtual Garden Tour! I know you're heading into spring and all of us winter bound northern hemisphere types would love to drool over your garden and pretend it was spring here, too.

If you have no scanning facilities, you could snail mail them to me and I'd scan them for you...let me know.

-- posted by Marge_Talt

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» Tim_Dutton - Big perennials

No Marge, I didn't succumb to the widening of the stream. As it happens, we have gone to the other extreme and have had three weeks without rain in November. Just as we were starting to think we would have to resort to the unenviable chore of watering the most essential plants in one and a half acres of garden with watering cans, it rained yesterday and all is well again, at least for another week.

As far as the H. mantegazzianum is concerned we have not experienced any difficulties with it so far. Being aware of its reputed properties we try not to brush against it with bare skin, and always use gloves when pruning bits off. Plants like that, once dead, we cut down and throw into our latest landfill site - usually an unwanted ditch or gully that we fill over the space of a few years with 100% organic matter. Eventually this all rots down and we can expect to be able to plant on top of it. So far the only completed landfill areas have been turned into lawn, and it has worked very well.

If you have success with the cardoon, make sure you try more than one plant. We started with four or five, and each year for the first three years we had one of them die. Then they outgrew their space and were moved in the winter while dormant. Now we have a single clump that covers an area of around 6 x 6 feet. It really needs a sheltered site as the flower stems can get very heavy, especially when it rains, and ours cannot stand up to the gales that we can get in November/December (late spring and early summer). I have just tied them to stakes so that they will not blow down this year. I hope! They do seem to like full sun.

As far as the horse manure is concerned, putting fresh horse manure on anything will do it no good at all, but we leave ours to compost down for about 12 months before using it. If it is full of worms, it is OK for the plants.

Yes, I have a scanner so can scan some photos for you. I have just taken a few, which will get developed in the next week or two I expect (film not used up yet). I'll have to take a few of the shady bog garden and a few of the choicer plants first, and then I'll try sending you a few.

Bye for now.

-- posted by Tim_Dutton

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» olly222 - Impressive giants

Hi there,
I'm new to the site but I saw your post and was hoping you might be able to help. A long, long time ago now I remember seeing H. mantegazzianum growing in a botanical garden and being so impressed! I'm sure the plant I saw must have been at least 16ft tall!!

I would love to get hold of some seeds for my garden, do you know of any suppliers who might be able to sell them to me?

-- posted by olly222

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» Marge_Talt - Re: Impressive giants

In response to message posted by olly222:

Hi olly222, Welcome to Gardening in Shade!

Well, I hate to tell you, but Heracleum mantegazzianum is now on numerous noxious weed lists; banned in the state of Washington, the UK and other states. The seed is listed in the Federal Noxious Weed Seed list.

I don't know where you garden, but you would need to check with your state or local government to find out if you could grow this majestic plant. It appears that it sets copious seed that is washed down waterways and colonizes them, creating problems in certain areas.

It has sap that is toxic to the touch and causes welts on the skin, which is something to keep in mind if you have small children anywhere around or are sensitive yourself.

The only seed source I have found is B & T World Seed, but if you live and garden in the US or the UK, it is going to be illegal to import this seed.

This is a magnificent plant visually, but it seems that, sadly, it causes more problems than growing it is worth these days:-(

-- posted by Marge_Talt

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