Tuesday, August 31, 2010

Lavandula dentata 'Pure Harmony'

Lavandula dentata  'Pure Harmony'
White French Lavender

This species of Lavender has a profusion of flowers at this time of year and the batch I have grown looks fantastic massed together. However despite the great cultivar name, I don't think you can beat the plain species with the lavender/mauve flowers. 'Pure Harmony' is just as hardy as the traditional form of French Lavender and would make a great addition to a garden where white flowers are chosen as the theme.
2017 update: i no longer grow this form.

Friday, August 27, 2010

Sideration:The use of green manure

White Lupin 
Lupinus albus

Trigonella foenum-graecum

This winter I grew these plants as green manure on my plot at the community garden. Both are just starting to come into flower and are at the perfect time for turning into the soil. According to my well thumbed copy of Rodale's How to grow vegetables and fruit by the organic method, green manure plants are one of the best soil conditioners ever discovered. 'They cost little, take little time to use and provide the answer to good soil tilth'. Every gardener who may not have time to make enough compost for the whole garden area can get the fertility build-up, biological activation and disease and insect resistance by planting green manures.
I am tempted to save some seed of the Fenugreek as it is such an aromatic Indian spice. In Hindi it is called methi and is a traditional ingredient in the spice mix panch phora . The "Greek" part of the name foenum-graecum means Greek hay.

Tuesday, August 10, 2010

Plant pathology: Problems with peas

Downy Mildew
 Peronospora viciae
This fungal disease causes the upper surface of the leaf to turn yellow while beneath the leaf a grey brown furry growth develops. This is worse during humid weather. Watering late in the day should be avoided.
Powdery mildew fungus (Erisphe pisi) showing as white powdery coating on leaves while parasitic fungi 'black leg' (Mycosphaerella pinodes) and 'chocolate spot' (Ascochyta pisi) cause brown or black marks or spots on the stems and leaves.
In Australia, the pea variety Greenfeast, a New Zealand selection from Lincoln, has long been regarded as having good disease resistance though it may not be entirely free from an attack by powdery mildew. It is a recessive gene in peas so that even wild peas from which the modern cultivars have been developed are sensitive to it.The theory behind this is that mildew is encouraged by the plant as it attracts beneficial insects such as ladybirds which appear to feed on the fungal colonies, thus protecting the peas from a worse insect invader.
Other resistant varieties include the American bred Knight, Kodiak, Mayfair, Rascal, dwarf Oregon Snow Pea and the sugar snap variety Super Sugar Mel. Not all these varieties are available here.
A degree of control of fungal diseases in peas can be achieved by spraying with potassium bicarbonate or by using a sulfur powder.

Plant Pathology:Black root in radish

Radish 'black root' Aphanomyces raphani
This fungal disease of radish causes dark patches to appear on the root which eventually splits open. Spores remain in the soil for many years and are spread by running water. A degree of control can be achieved by improving soil drainage and practising good crop rotation.

Onion Thrips

Damaged foliage with silver grey flecks and twisted bent growth indicate onion thrip.
Onion thrips, Thrips tabaci are important because they carry the disease spotted wilt which affects a wide range of plants including tomatoes and ornamental such as dahlias. This insect is found in all onion/leek/garlic growing areas of the world and is mainly a problem during warm dry weather and less of a worry during cool rainy periods. Thrips can be hard to detect at first as the young wingless creatures, which are pale yellow, congregate in the throat or 'chit' of the plant feeding on the newly unfolding leaves. The adults spend their time on the exposed upper surface of the leaf where they feed by piercing the the tissues and sucking on sap.The clever female thrips are able to reproduce without mating resulting in many generations being produced within a season. The female is a tiny light or dark brown insect about 1.3mm long with two pairs of narrow wings fringed around the margins with fine hairs. The male is smaller. Both are strong fliers and are easily carried by wind to infect a large area. Control can be achieved by inspecting the throats of young plants for early signs of infestation and spraying appropriately. Removing broad leaf weeds where thrips may lurk and providing good irrigation during dry weather helps keep this pest at bay.

Bolting in seedlings

When growing vegetables at this time of year,and as the days lengthen and the temperature fluctuates, you can encounter the problem of bolting , plants going to flower and seed before producing any leaves. Asian greens ,Brassicas for example , such as this Chinese Broccoli are particularly susceptible to this. In this case I left the seedlings for too long in the tray, they became drawn and stressed from not enough moisture and nutrients. After planting them out they went into transplant shock and the low night temperatures accelerated their demise.
Joy Larkcom goes into more detail about bolting in her excellent book, Oriental Vegetables The complete guide for the gardening cook. Her suggestion of growing seedlings in a module so that individual plants are able to develop a good root system is one way of overcoming the problem as well as germinating seeds at at reasonably high temperature of 18C degrees -25C. Low temperatures in the early stages of growth is the single most important factor leading to the initiation of flowers instead of leaves. Young plants need to clock up a certain number of heat units to prevent bolting : once this has been done they can be subjected to lower temperatures without damage.

Sunday, August 8, 2010

Plant pathology:Grey Mould on Italian Chicory.

Cicoria pan di zucchero
Grey Mould (Botrytis cinerea) is a fungal disease which is more common during cool wet weather such as what we have been experiencing lately. Brown rotted areas appear at the heart of this Italian chicory variety and this can be accompanied by greyish furry growth. The plant will eventually collapse but should be removed at the first sign of any damage and placed in a bin.

European Earwig

European Earwig, Forficula auricularia
(photo from Wikipedia)
Working at my community garden plot yesterday I encountered this insect for the first time. I have come across the smaller native species before but not this one. Peeling back layers of mulch they scattered everywhere, all with their forecep pincers raised in defence. Apparently this earwig was first recorded in New South Wales in 1934 and can be a pest amongst fruit and vegetable crops.In my case they had been dining on small seedlings and leaving them with a ragged appearance. A solution for dealing with them was given on Gardening Australia last night. Leave out a shallow dish of oil with some added soy sauce and the earwigs which feed at night will come running to it.

Friday, August 6, 2010

Plant pest Mites

Witches' Broom on Hornbeamdistorted growth caused by mites
Plant Mites are arachnids and thus related to spiders, ticks and scorpions. Most gardeners are familiar with the damage some of them can cause to foliage though they are barely visible to the naked eye and have often departed before their 'work' becomes noticeable. At the moment, I have a batch of the shrub Brugmansia ,the new growth of which displays stiff downward cupping on the top leaves and twisted older leaves. This is caused by the Broad mite (Polyphagotarsonemus latus) which is most active during warm humid summer/ autumn weather.The damage to the "Brug" was probably done months ago when the new leaves were quite tiny. The other mite of concern to gardeners is the 2-spotted mite (Tetranychus urticae). The warm dry weather of early spring suits this pest best. The first sign of an infestation is a speckling or mottling visible on the upper surface of the leaves. This is caused by the mites feeding on the underside of the leaves, where silver and rusty marking can be seen as well as some fine webbing. This mite has also been given the name of red spider mite as the adult females develop a red orange colour during winter. Plants which are stressed due to lack of water or low nutrient levels in the soil or pot are often more susceptible to infestation from this mite. So how to deal with them?...... I use the excellent Neem oil or a wettable Sulphur spray or dry Sulphur powder. You can also use biological control by releasing predatory mites (Phytoseiulus persimilis, Amblyseius womersleyi and Typphlodromus occidental) or ladybirds (Stethorus sp). These are readily available from specialist suppliers.
It is important also to remove mite host plants especially low growing herbaceous weeds. Mites are distributed around by wind, birds or man and can travel on clothing, garden tools and farm machinery. Keeping your plants healthy and having a bio-diverse garden with a range of plants to attract beneficial insects goes a long way to keeping the pesky little mites from doing much damage.
Two Spotted Mite 0.5mm

The red-legged earth mite

Broad mite egg 0.1mm

Brugmansia showing Broad mite damage

Tuesday, August 3, 2010

Houseleek, Sempervivum

Sempervivum tectorum

I have this one pot of houseleeks and during winter the outer rim of the leaves take on a faint pink tone. A friend who collects succulents has an enormous range of these mountain loving plants but the finer distinctions between the species seems barely discernible to me. Some grow quite large and have black and purple leaves and others have that fine mesh of 'cobwebs' covering them.The old Dutch common name for Sempervivum is Donderbloom, or 'thunder flower' because to have it growing on the roof was a charm against being struck by lightening. The Greeks regarded it as an aphrodisiac and named it hypogeson because it grew on the high parts or eaves of buildings. The Old English name leac, from the Anglo Saxon became 'houseleek'. Other common names abound , the most interesting being 'Jupiter's beard', as it is under the dominion of Jupiter and symbolizes vivacity; and the very amusing 'welcome home husband however drunk you be'.

Sunday, August 1, 2010

Beauty & the Beast...a malodorous Arum

Welcome to the 'Honeymoon Hotel' for flies. On a cold foggy wet day in mid winter, when bees are notably absent from the garden, the only chance this Arum Lily has of being fertilized is to let off the smell of a refuse tip, a dung heap, a dead animal or a combination of all three. Most of the smell emanates from the shiny black rigid protuberance know as the Spadix . The adjoining petal like leaf or Spath is funnel shaped and acts as the landing strip for carrion insects. It often appears like a piece of uncooked liver or something splashed and blood stained.The actual flowers are minute and hidden down at bottom of the Spadix and appear as separate rows of male and female flowers. To make sure that the insects get to them, the Arum sets up what is known as 'trap-flower syndrome'. As they approach the centre, a treacherous slide of oiled cells sends then tumbling through a ring of hairy filaments at the entrance to the chamber. These filaments not only mimic the fur of a dead animal but stop larger insects from visiting which could damage the chamber. Once inside the insects are imprisoned for 24 hours and fed on a sticky sugary solution exuded by the female flowers. After this time the male phase begins, the filaments shrivel and the insects are released and showered by male pollen on departure.
And for Arums there is always the 'back up plan'. Underground there are lots of starchy tubers which are slowly being manufactured, storing food and taking over the role of parent when the heat of summer makes the whole plant shrivel and disappear until autumn rains starts the cycle all over again.