A Northumberland Alpine Gardener's Diary
This entry: 20 October 2010 by John Richards
Northumberland Diary. Entry 163.
A new rhodo bed
I find mid October an excellent time to undertake major projects. Routine chores such as mowing, clipping, edging, weeding, propagating, watering, feeding and so-on have subsided to a minimum as the weather cools and the plants shut down for the winter, but the soil is still fairly warm, easy to work and the days are still bright and of a reasonable length. I have had it in mind for some time to develop the area close to where we had the large lime felled, and the diary was clear this week, so I started last Thursday, and have just finished (Friday and Sunday were spent doing other things however).
I grow a fair number of smallish rhododendrons (and a few larger ones) in this half-acre garden. However, twenty years after many were planted, some are looking distinctly the worse for wear. They have been invaded by tree roots, or perennial weeds, shaded as other plants grow, run out of goodies, so that in many cases they were dry and starved at the root. Also, many had become drawn in this shady garden. The biggest problem is the most recent, and I have discussed it before. Wanting my cake and eating it, I underplanted Ericaceous subjects with bulbs as well as primulas, meconopsis and the like. Rhododendrons and bulbs just do not mix; the bulb foliage looks a mess after flowering, just as the rhodos need to look their best.
So I needed a bed where I could grow Ericaceous subjects in isolation. Felling the lime tree has provided just the opportunity, as areas that were shaded, subject to a rain of tree-litter and sooty mould, and full of root have become free. Also, we plan to stool a large Acer capillipes as soon as the leaves fall, allowing much more light to fall on this area.
There was in fact a small bed where I planned to build the larger one. Originally I grew Meconopsis and petiolarid primulas there, but it has been invaded with tree roots and became very dry in summer, so virtually nothing except weeds (and a very large Meconopsis ex M. superba which is probably hybrid with M. paniculata) survived there. This bed had been raised slightly with sleepers (railroad ties for our transatlantic cousins). The first job was to remove and store the sleepers and clear the weeds.
The next job was to remove the turf from where the new, much larger bed was to go. Usually I remove the turf and stack it. (I rarely use the rotted turf however as our greasy clay-based soil makes for a very heavy loam). On this occasion I knew that I intended to raise the bed considerably, so I merely reversed the turves to let them rot in situ. It is important that the reversed turves are not placed too close to the edge of the bed as this can give them an opportunity to resume growth.
The area now under cultivation is about 10 x 4 m at the widest. As I said, I planned to raise the bed considerably. Many of the beds in this rather shady, sheltered, north-facing, sloping garden with its heavy soil are raised to improve not only drainage but also air circulation and insolation, bringing plants up into airflow and sunlight as much as possible. When the large lime was felled in August, I asked the contractor to leave me about 20 of the largest sliced 'roundels' from near to the tree's base. I have used material like this to edge beds before. The roundels are very heavy, perhaps 200 kg each, but they are surprisingly easy to manoevre by rolling on their edge. The trick is to get them upright in the first place. A trench just wider than the roundels was dug around the edge of the planned bed. The roundels are sunk with their flattest edge on top. If the trench is the correct width and depth (about 40 cm deep) the roundels are very stable from the start. Nearly all went in without difficulty. However, a few took much more toil and sweat before their position and height was acceptable! Here are the first six in position.
And here are all the roundels in place. I was able to use 14 in the end, leaving me six of the biggest spare. I am not sure what to do with them. On a previous such occasion I tried using them as path pavers, but they became very slippery in wet weather. They would be better with wire netting pinned on however. Maybe our new next door neighbour who has purchased wood-burning stoves will take them to axe. They are VERY big to shift however!
So now it was a simple matter of filling the container! This is not a small volume. I reckoned that the surface area to be filled was about 30 sq m, and the average depth 30-35 cm, so that the volume was about 10 cu m. It took 32 barrowsful to fill, which makes every barrowful roughly 300 litres of material, which I guess was about right. All the material came from the garden, showing the value of properly managed humus conservation! (if that sounds smug, well, yes, I have been making good garden compost and leaf mould for all the 20 years we have been there, and I do think it is a vital (and green) asset).
I did not mix the materials, except afterwards, while planting. The garden compost goes in first, because I cannot get compost hot enough here in this shady garden and so the material is full of annual weed seeds; the deeper it is buried the better! There were 12 barrows of this, and then 10 barrows of old potting soil. Because this is mostly from alpines and bulbs, it is very gritty, thus providing good drainage at root level. Here is the potting soil going on top of the compost.
The leafmould goes in on top. Because this bed is principally designed for dwarf rhododendrons, this relatively nutrient poor, humus-rich, acidic, water-absorbent material, very like peat in texture, is an ideal medium. There were another 10 barrows of this two-year old mould, very timely because I needed the space to put the one-year old stuff in time for the new leaf gathering next month.
As you can see, the sleepers have now been put in place, in the centre of the bed along its main axis. These are principally to provide access to all parts of the bed. I do think that in this type of acidic humus-rich bed it is vitally important that the soils remains open and fluffy so that it is very important NEVER to step on the soil.
So all I had to do now (today) was to plant it! Rhododendrons move well, and they are easy to lift, but a good deal of time was spent cleaning them up, pruning back dead twigs and making sure that the rootball was free of perennial weeds. Here is one view with some classy subjects such as Rh proteioides (formerly in a trough which it was outgrowing), Rh. pronum (propagated from the famous Kilbryde plant and a welcome gift from Peter Cox), Rh. bureavii, Rh. balfourianum and some cassiopes.
Slips of Rh. forrestii have been put to drape over the front, and Rh. keleticum, Rh. radicans and Rh. pumilum are other species used in a similar way. Nothing has been bought in (this time). Everything was either moved within the garden or propagated.
Further back, larger species have been used including the pink Rh. chamaethomsonii, Rh. pachysanthum, Rh. pemakoense, Rh. myrtilloides, Rh. 'Chikor' (both grown very leggy) and Rh. 'Snow Lady'.
As can be seen from the last photo, I decided to move, heart in mouth, the big Meconopsis, as it was in the wrong place. It was well watered in. Here is a final view.
Just a few out-of-season flowers to finish with. In the last photo it is just possible to see Asterantha ovata. I have had this South American gesneriad for many years, but it rarely does much and was becoming swamped with oak fern (a real menace here). However I found it was producing a few of the wonderful scarlet flowers, and as a reward to have moved it. It is amazing that it survived last winters freeze.
Two out of season primulas, neither of which has been in my care for very long, and both very scarce in cultivation. First the Slovenian endemic P. carniolica, and then P. serratifolia from the Cang Shan above Dali, Yunnan.