Reverse litmus, Hydrangeas and soil pH

I was being the “expert” on a school plant stall recently when I was questioned about how to change the colour of hydrangeas, specifically how to make pink hydrangeas blue and if nails and steel wool added to the soil would work. Coming from a science background I have to forget the litmus colour test where blue turning red indicates acid and red turning blue indicates alkaline. The hydrangea indicator is the reverse of litmus. A pink hydrangea indicates alkaline soil and a blue hydrangea indicates acid soil.  Purple indicates a neutral solution with litmus and a neutral soil with hydrangeas. White hydrangeas are not affected by soil pH although I have noticed a thin blue or pink margin around some.

pink and purple hydrangeas Dec 2015

I have done a bit of follow up research and find that aluminium ions are the key for the hydrangea pH indicator. In acidic soil aluminium is available and will change the pink to blue. In alkaline soils the aluminium becomes immobile as aluminium hydroxide and the hydrangea is pink.

pink and white hydrangeas with a purple at the very back Dec 2016

The mountain soils are generally acid and we would assume therefore that our hydrangeas would be blue. We actually have a few neutral purple hydrangeas and many that are pink. A soil test  in the vicinity of the pink plants revealed  pH6.5. This is a bit close to neutral for a good blue as aluminium begins to become unavailable above pH5.5. The plants that are pink may have their roots into the lime mortar of the rock walls, lime may have been added to the garden in the past or there may be insufficient aluminium in this patch of soil. Achieving a pink hydrangea is just a matter of adding lime but turning a pink hydrangea blue is more difficult. The usual method is to add an acidic aluminium complex such as aluminium sulphate. This will kill the plant at high concentrations and kills the microorganisms in the soil so for us is not an option.  Rusty nails, coffee grounds, citrus peelings, pine needles, pine bark and organic matter generally will all have a slightly acidifying effect.  As there are purple plants in the bed there must be some aluminium present. The bed in the photos was renovated earlier in 2015, see Mop Head Hydrangea Bed Renovation, and has flowered very well considering the severe treatment it received.  We will stick with our present colour combination. We are adding organic matter in the form of compost but I think a colour shift is a long way off.

Composting notes

Slime mould

Black soldier fly larva

We found a beautiful slime mould on the side of our compost bay a few weeks ago. Slime moulds feed on decaying organic matter and in this situation are probably associated with the leaf mulch we layer into the bay to absorb food scrap moisture and provide carbon. The yellow fruiting bodies are produced when the mould is under stress, it may have been the onset of the very warm weather. I photographed the mould in the morning and by the afternoon it had dried up. A common name for this mould is dog vomit mould which is especially apt once it has dried off.

After the run of hot weather I found a soldier fly larva on a freshly constructed compost pile. These larva are brilliant decomposers and are being used to break down food scraps containing meat and dairy. They are very fast composters and once the larvae are fully developed they separate themselves out from the composting material so can be harvested for fish or chook food. They need higher summer temperatures for effective composting and so we only see them here in very warm weather.

PLA drinking straws in the veggie scraps

Up Beet are using PLA bioplastics for some of their takeaway containers and their  drinking straws. Some of the straws end up in our compost. These straws are made from Polylactic acid derived from corn plants. The material will break down into organic components under hot composting conditions. The heat required is usually only generated in industrial composting systems but we do generate up to 65 degrees C in our compost piles so we cut them up and throw them in.  They haven’t  been coming in for long but on a recent turning of the pile we noticed they had become very brittle and were falling apart.

A hot few weeks

We continue without rain and are hoping that one of the wandering thunderstorms currently about will grace us with a downpour and give the plants a bit of respite. We have been watering our wedding lawns with sprinklers before 10am and all the garden beds with soaker hoses or sprinkler hoses installed. We still have plantings looking good and I think our continual composting and mulching is paying off.

Goldfish and reflected Dutch elm

The rock pool is a very pleasant place to be in this weather, the dutch elm is starting to lose a few leaves but there are still plenty to give a green reflection.

Dark pink Lagerstroemia indica

The crepe myrtles are loving the heat and the dark pinks ones are looking spectacular.

Plectranthus argentatus

Plectranthus ciliatus

Our neighbour Don is a great plectranthus fan for planting in shade and he has given us cuttings of both these photographed. The silver leaved one is an Australian native and the purple leaved one from South Africa. Plectranthus ciliatus roots from stems as they spread and so does have weed potential. It is the only plant I have had success with in dry shade under conifers. The nerines are having a good season too. I have planted  pink Nerine bowdenii,  the red Nerine fothergillii  var. major and the white Nerine flexuosa “Alba”. The white was planted this year and hasn’t flowered in it’s first season unfortunately.

Nerine bowdenii

From Canberra swimming pool to secret garden

The swimming pool in Fiona’s Canberra garden was no longer in use with children grown up and away from home so Fiona decided to repurpose the area as a sunken native garden, using many plants endemic to the Canberra region.

The pool in use in 2006

The vinyl lining gone and the project begun 2013

 

 

 

 

 

 

 

Completed garden awaiting an umbrella and a garden setting 2016

Fiona reused much of the concrete from the pool sides to create her new terraces and steps and created a half gabion effect in her retaining walls, using mesh as the cage and existing concrete and pebbles for the fill. Netting holds the pebbles in place behind the weldmesh. The posts from the old pool were still in good shape so Fiona left them in place and retained the capping for stability around the curves.

 

 

 

 

 

Wall detail with Callistemon sieberi and Veronica perfoliata

The  soil in this patch of Canberra is  alkaline, helped along by all the concrete. Fiona only had subsoil clay to work with so  mixed it with coarse sand and compost to form the garden beds. The Canberra region has a range of soil types so not all endemics will grow. Fiona tries to select plants she hopes will cope but removes them after a couple of special treatments if they don’t establish.

 

 

The rockery over a vulnerable sewerage line with non damaging  hybrid Brachyscome angustifolia, and the endemics Bulbine glauca, Viola hederacea and Scleranthus biflorus

The stairs and path composed of old clay fill dug from the pool site, it’s a good colour and very alkaline so weed resistant

 

 

 

 

 

 

 

 

The bog garden

The bottom of the garden becomes boggy in wet weather and Fiona has planted in some bog plants, seriously restricted on account of the sewerage lines. The bog circle contains Lythrum salicaria, Isolepsis nodosa, Baloskion tetraphyllum and a Juncus sp.

 

 

Scleranthus biflorus flanked by Kunzea ericoides “Snowman” with Chrysocephalum apiculatum and Acacia dawsonii all endemic in some form

Eremophila nivea “Blue velvet” a grafted Eremophila hit hard by frosts but recovered after hard pruning.  Acacia boormanii behind

We found native bees visiting the grey Eremophila. We think they are blue banded bees from the Amegilla genus. The Scleranthus is known as Canberra grass.

 

 

 

 

 

 

 

One of the bluebells of Canberra Wahlenbergia communis

The floral emblem for Canberra is the bluebell Walhenbergia gloriosa. Fiona has a few species growing, the one I photographed volunteers between the pavers above the secret garden.

 

 

 

 

Fiona in her secret garden