Soil and Feeding
The soil performs three basic functions for plants:
- The soil should give the plants a chance to root down and hold firm. In cultivation, this means the soil must not be too dense and prevent the roots penetrating. Furthermore, the soil must be well-drained so that surplus water can run away and so avoid root rot.
- The soil needs hold a certain amount of moisture for use by the plants.
- Finally the soil should provide the plants with necessary nutrients for the growing season. Plants in pots rapidly exhaust the soil and need regular feeding or repotting when required.
After repotting, plants get all the nutrients they need from the new soil, but they soon use them up and need feeding. There are two main groups of fertilizer which differ in content. The so-called complete fertilizers contain nitrogen (N), phosphates (P) and potash (K). It is preferable to choose fertilizers with a low nitrogen content, but as the composition of all fertilizers varies considerably, it is best to vary the brand from time to time to avoid a deficiency of any particular component. Complete fertilizers also contain trace elements besides the normal components. These are required by plants, but with sufficient use of complete fertilizers and regular repotting, it is rarely necessary to use special fertilizers with these trace elements. However if you feel the need to use trace elements, please carefully follow the instructions, as an overdose can kill the plants. During the growing season regular but light fertilizing is recommended. Repotting small or slow-growing species is not necessary every year. Faster-growing species, however, can exhaust the soil after a year, despite regular feeding, although increasing the dose can delay the necessity to repot. However the danger of this system is that the plants can become torpid and susceptible to disease.
Monadenium rubellum
Watering
The idea that succulents grow in dry places is not quite correct. The majority grows in areas where water may not be available in certain periods or only as fog or dew. As far as possible, the requirements of individual species need to be considered. When it is hot and plants are growing, they may need as much water as ordinary plants.
The choice of pot has a bearing on watering. Basically there are two types:
- Unglazed earthenware pots were for some time the only type available. These allow water to evaporate through the sides, and also allow air to reach the roots, discouraging rot, a particular advantage for moisture sensitive species. Roots can however be damaged by cold due to evaporation.
- Glazed earthenware and plastic pots prevent evaporation through the sides. This means they need less watering, but increase the risk of roots being damaged by excess moisture. Plastic pots can also get very hot in the sun and cause roots to be burnt.
The golden rules for euphorbias are as follows:
- If in doubt, DON’T water!
- Just because euphorbias can survive drought, does not mean that they need it. In fact in the growing season regular and copious watering is required.
- Most species do not appreciate dust dry soil in the resting season, and need a little water from below, or even carefully from above.
- It is better to water heavily once, than give little drops often. Heavy watering wets the whole pot of soil encouraging a healthy root growth.
- It helps to add more drainage material to the soil of moisture-sensitive species when potting. This means that plants can all be treated the same when watering.
The best time to water in the warm season is evening as plants take up more water when it is cool, and less water evaporates away. Early morning watering is also acceptable and may even be better in the winter months.
Jatropha vaiifolia
Temperature
Although succulent euphorbias are suited to warm, dry conditions, the temperature requirements differ widely. High summer temperatures or wide diurnal fluctuations are not a problem, but minimum winter temperatures vary. As a rule of thumb, species coming from Arabia, Central and West Africa and the tropical and sub-tropical parts of the Americas need 12-14 °C in winter. Madagascan and East African species need 10-12 °C, while species from North and South Africa can endure temperatures below 10 °C if kept dry. In fact some South African species can survive frost if temperatures rise rapidly the next morning.
In general ventilation is good for the plants. Big temperature fluctuations between day and night are also beneficial encouraging winter rest when the cool autumn nights arrive. Air humidity is closely related to temperature. While euphorbias enjoy high humidity when growing and temperatures are high, humidity needs to be very low during their winter’s rest, when temperatures are lower.
Euphorbia persistentifolia
Producing, harvesting and sowing seed
As euphorbia seeds have a limited shelf-life, they are rarely offered commercially.
Pollination can be achieved using a brush with fine hair, and transferring the ripe pollen from one cyathium (flower) to the stigma of that of another plant. Be sure to clean the brush thoroughly after use to avoid unexpected hybrids! Another way is to remove ripe stamens using fine tweezers and using them immediately to effect a pollination.
Pollination of Euphorbia bupleurifolia
Transferring pollen to the stigma
Using tweezersHarvesting seeds presents a problem. The fruits of euphorbias are hard, woody capsules, made up of three segments, each containing a relatively large seed. When the capsule ripens, it explodes and scatters the seeds over amazing distances. A tried and tested method is to put a cotton pad around the ripening capsule and so prevent the seed from flying away. Nylon stockings can be used in the same way. In the case of particularly valuable seed, the whole plant can be enclosed in thin gauze or nylon.
seed capsules
Euphorbia bemaharensis
Euphorbia geraldii
Euphorbia maleolens
Monadenium pseudoracemosum
A convenient and safer method to save the seed is to apply a thin layer of glue to the already ripened capsules to prevent them bursting open. Fully dried capsules can sometimes be collected whole and opened carefully from the base.
applying a glue layer
Euphorbia and Monadenium seed
Euphorbia alfredii
Euphorbia groenewaldii
Euphorbia lupulina
Euphorbia meloformis
Euphorbia nubigena
Euphorbia pugniformis
Monadenium coccineum
Monadenium mafingense
Containers suitable for sowing are above all shallow plastic pots or trays as they do not dry out so quickly and can easily be cleaned and disinfected. The sowing medium should be light and poorer in nutrients than normal commercial plant compost. A mineral soil can also be used, such as fine to medium grade sand to which can be added a little finely sifted peat. The soil should be thoroughly wetted by standing the containers in water.
As conditions in the containers are also favourable for fungus growth, sterilisation of the soil is recommended (about 20 minutes in an oven at 120 °C with the soil evenly spread on a sheet). The soil can also be disinfected with a fungicide such as Chinosol, but please read the directions carefully or the tender seedlings may be damaged as they germinate.
Fungus in sowing soil
Sow the seeds evenly and not too thickly on the surface of the soil, press lightly and cover with a very thin layer of soil or sand no more than twice the thickness of the seeds.
During the period of germination, always keep the soil moist as letting the soil dry even once can result in heavy losses. It can be helpful to cover the trays with a transparent plastic dome or cling film.
The temperature at night should not go below 18 °C, although by day it can rise as high as 40 °C. 25 °C is ideal. Basically higher temperatures bring faster germination, but full sun should be avoided to prevent the young seedlings scorching.
Raising seedlings in a box
Sowing box
Containers and pot
Soil Thermometer
Germinated seedlings
The short viability of euphorbia seeds should be noted. The percentage germination can fall to 50% after only a few weeks. In general seed needs to be dry and stored at 5 °C in air and water proof containers. Dampness or higher temperatures cause the viability to decline more quickly.
As rainfall is irregular in habitat, not all seed germinates at the same time to ensure some seedlings survive. Germination tends to occur in waves, for example after one week, 8 weeks and 15 weeks. Furthermore, the germination period also varies from species to species.
Seedlings
Euphorbia alfredii
Euphorbia brevirama
Euphorbia bubalina
Euphorbia enopla
Euphorbia gottlebei
Euphorbia meloformis
Euphorbia rosii
Euphorbia thinophila
Vegetative Propagation
Propagation of euphorbias from cuttings is the easiest and quickest method for many species, and is also a way to prune an old plant back into shape. Cuttings should be taken with a sharp clean knife, if possible laying the plant down on a clean and smooth surface and using a pulling, rather than pressing motion to obtain a clean and clear cut. Branching species should be cut if possible at the branching point. Solitary plants such as E. bupleurifolia or E. piscidermis can be decapitated to encourage production of side shoots which can later be removed and rooted.
The best time to take cuttings is in the spring when growth starts, but summer is also suitable. Cuttings taken in autumn or winter have little time to root, and so cuttings should only be taken as an emergency to rescue plants suffering from root rot.
The latex appearing after cutting must be completely washed away in a glass of water or by spraying. Cold water stems the flow quickly as does brief exposure to a candle flame or match.
Euphorbias with large leaves should have leaves just above the cut removed with a knife. The cut surface should be left to dry before planting, one or better several days for leafless species. Leafy Madagascan species need only dry a short time. Dusting the cut surface with a hormone rooting powder will help roots form. For euphorbias we recommend 0.1% naphthyl acetic acid and not indolyl acetic acid which is usually found in shops. The planting medium can be the same as for seed sowing with the addition of some sterilised drainage material.
Rooting can take longer than expected but is accelerated by raising the soil temperature to around 25 °C using a thermostatically controlled warming mat. Direct sun should be avoided.
If unrooted cuttings dehydrate, they can sometimes be saved by soaking in water at room temperature until then swell up again and can be replanted.
Euphorbia greenwayi var. greenwayi
Euphorbia myrioclada
Euphorbia similiramea
A fast rooting method, which does not suit all species, is to stand cuttings in a narrow glass and fill up to 2-3 cm with water. Rooting can occur in 10-14 days.
Rooting cuttings in water
Cuttings in water
Euphorbia cotinifolia ssp. cotinoides
Euphorbia guiengola
Some euphorbias that can be rooted from side shoots continue to grow as branches and do not form the typical plant form. The medusa-head species are in this group as well as E. brevitorta, E. groenewaldii, E. tortirama and others. For these the so-called two-step cutting method is required. First a cutting is taken in the normal way. When this has rooted, a second cut is made just above the point where roots have formed and the cut is treated in the normal way. The tip can be re-rooted and when large enough can be cut again. The rooted stump will normally produce a plant of form typical to the species and this can then be removed when large enough from the mother cutting.
Some Madagascan euphorbias (E. francoisii, E. cylindrifolia, E. pachypodioides, E. ankarensis, E. millotii) have been successfully propagated from leaf cuttings. Leaves are gently pulled from the plants (not cut) and put into cubes of rock wool which are then placed on coarse sand in a tray. The surface of the sand should be covered with water (putting the leaves directly into damp sand also works, although with greater losses). Hormone rooting powder and fungicide assist the process. Both gentle heat or a cool position with a plastic cover to increase humidity, should produce the desired result. After 40 days the plants are sufficiently well developed to be potted.
Leaves of E. decaryi, E. primulifolia, E. moratii, E. cremersii and E. decidua will produce roots but do not develop plants. They remain as rooted leaves.
Finally a few words on the toxicity of the latex. Even small amounts can cause painful skin irritation. If you get it on the skin, it should immediately be washed off thoroughly under running water. On no account let the latex come into contact with the eyes or mucous membranes.
Grafting
Grafting euphorbias is of interest for several rare and difficult species as when they are on more vigorous easier stocks, they are easier to keep, grow faster and produce more flowers and seeds.
The method of grafting euphorbias differs little from that of other succulents, except in one important aspect. The latex must be washed or sprayed off until hardly anything remains. After the latex flow has stopped, a further 1-2 mm slice can be taken from both surfaces without a new latex flow starting.
Both plants need to be at the start of the growing season. The stock should be cut as near as possible to the growing tip, as here the vascular bundles are dense and not yet woody and will feed the scion in the best possible way. Where possible stock and scion should be of similar diameter. The cut surfaces are held together with elastic bands in cross style, over the plant top and under the pot. The plants should be left in an airy and shady place for 7-10 days before the bands are removed.
Almost all euphorbias are suitable as stock, but it should be remembered that especially strong stocks may change the appearance of the scion. At the same time, however, they may also increase the chances of flowering or branching, which is a positive effect for rare and difficult species.
Strong growing stocks are E. ingens, E. candelabrum, E. canariensis, E. grandicornis and E. trigona. A moderately strong stock is E. fruticosa. A less vigorous but reliable stock is E. obesa. E. mammillaris, which is often used, is reliable but seems short-lived. For the caudex-forming Madagascan euphorbias, such as E. capsaintemariensis, E. moratii, E. primulifolia or E. ambovombensis, Rauh (1987b) recommends as a stock E. milii var. hislopii.
Finally a further reminder in this section of the toxicity of the latex. If it comes into contact with the skin, it should be thoroughly washed off under running water.
Pests and DiseasesEuphorbias are not only very attractive plants, but they have a big advantage in that in general cultivation is easy and they are less susceptible than many other succulent plants to pests and diseases. They are therefore suitable for greenhouse cultivation or the window-sill.
Whether or not a plant is flourishing is not always apparent, but as you get more experience with euphorbias, you get to know their growing and rest periods and then more easily spot changes which might indicate a problem. A reliable sign is change of colour, in particular pale or deformed sections indicate pest damage or a lack of nutrients. Also lack of growth can point to a problem – the main growing season for most species is spring and autumn, with many plants taking a mid-summer rest. The dropping of flowers usually means too much water, or a poorly drained soil, whereas the drying off of flowers, especially with the Madagascan species, indicates a lack of water.
Corking means a change in the outer layer of skin (epidermis) of the plant. Most commonly this is a brown colour accompanied by a thickening of the tissues. The cause can be strong sunshine on previously shaded plants, but corking is also a natural phenomenon in habitat with aging plants. Although we may think corking is unattractive, it is a plant’s natural reaction and needs no treatment.
Mealy bugs are the commonest pest on euphorbias. They are up to 3 mm long, oval, similar to wood-lice but whitish, easily distinguished by the white, cotton-like substance they produce. The adults prefer inaccessible areas and so may be difficult to find unless plants are very carefully examined. In an infestation of E. flanaganii at the shoot tips, the plant reacts by the whole branch drying back and being shed. Infected plants should be isolated to prevent spread of the pest. As First Aid, the cocoons containing oval, yellow, shiny eggs, the small yellowish larvae, and the whitish adults, can be removed from individual plants with a pin. However, since the mealy bugs prefer inaccessible areas, even in the soil around the plant’s neck, generally this only achieves a reduction in numbers.
Treatment is with regular spraying with pyrethrum, nicotine solution or mineral-oil based insecticides. Also regular applications or sprays with soft soap and spirit helps against the drought loving mealies.
Mildew and other fungal diseases
Mildew appears as a white, powdery film on parts of the plant. The disease can be caused by too high humidity, insufficient ventilation, too little light, plants placed too close together, or low resistance to infection from lack of nutrients. So it follows that the best protection from mildew is improved cultural conditions.
If however mildew strikes, the infected plants must be immediately isolated, and in some cases the infected parts must be removed and destroyed. Regular cleaning of the infected parts can help, otherwise chemicals need to be used. As there is no specific fungicide on the market for mildew on euphorbias, you will need to choose one for mildew on roses or ornamentals.
One disadvantage of a systemic fungicide is that is cannot be used in the rest period when no water is being taken up by the plant. At these times contact fungicides need to be used such as sulphur or sulphur preparations, or sprays. Foot sprays against fungal infections are very effective and harmless to humans.
Some euphorbia species produce abundant nectar in the flowering season. If this is not collected by hover flies or other insects, mould can also develop on it. This does not directly damage the plant as it disappears as the nectar dries, but it can interfere with pollination. Untreated, the mould can recur every year in some plants. It can be dealt with in the same way as mildew. Finally, there are other types of fungi living in the soil which can spread and block air spaces. In this case depotting is the answer, cleaning the roots and repotting in fresh soil. Frequent applications of 1% Chinosol will also work.
Please read carefully the manufacturer’s safety instructions before using any chemicals.
Red spider mites are about 0.5 mm, light brown to reddish in colour. The winter form is terra-cotta. Under a lens, two dark spots can be seen on the back which differentiates it from the 1-2 mm red spider, with which it is often confused due to the similarity of the name. The true red spider is beneficial and eliminates small insects including red spider mites. The mites prefer to feed on young growth. An attack is usually seen by white or yellow mottling on the infected plant. The web, protecting the youngsters, is not so easily seen.
Infected plants should be isolated and the plants repeatedly doused with lukewarm water. The mites can be treated chemically with so-called acaricides. An alternative is biological treatment with a parasitic mite, which feeds on the juvenile stage of the red spider mites. As red spider mites multiply very quickly, the parasites need to be introduced at the first sign of an attack in order to put a stop to the rapid spread.
Root mealy bugs look just like normal mealy bugs and produce the same white cottony substance, but feed exclusively on the roots, where they can sometimes remain undetected until repotting takes place. They are smaller than mealy bugs, whitish, covered in white waxy threads, and very mobile, enabling them to spread to other pots. Root mealy bugs can be eliminated by a very thorough washing of the roots, and a final dip of the soil-free root ball in a solution of contact insecticide. Especially some monadeniums seem sensitive to root mealy bugs.
Root rot or wet rot can affect euphorbias if the soil remains too wet for a long time, or if too much water is given too quickly after the root ball has dried out completely in the rest period. Weakened plants can easily succumb to fusarium fungus, leading to root rot. The disease manifests itself with brown discolouration of the plant neck, spreading to the whole plant, the inside of which turns to a soft, colourless jelly.
The only cure for root rot is to cut off the still unaffected parts of the plant, but generally this only works during the early stages of the disease.
An attack of sciara fly can be noticed when the 2-3 mm long black flies come up when the plant is moved. The adults do not damage the plants, but the larvae do. They are around 5 mm long, glassy, legless and with a black head. They are most dangerous in seed trays, as the young plants need constantly moist conditions which are ideal for the larvae.
If there is an outbreak in a seed tray, the best solution is to remove undamaged seedlings, taking care no soil goes with them and replant afresh, for safety watering with a contact insecticide. New egg-laying can be avoided by covering the surface of the soil with a thin layer of sand. The sand dries quickly and discourages the female sciara from laying her eggs in the soil. Adults can be trapped using the yellow sticky strips.
The drying back of shoot ends is not a disease, but the plant’s natural reaction to excessive dryness or lack of nutrients. If it occurs, plants should be repotted into a more moisture-conserving soil, or watering should be judiciously increased. In some species, tip die-back is quite normal, E. gariepina for example, or of outer branches, E. tridentata for example.
The tobacco mosaic virus (TMV) is a virus that infects plants causing a characteristic mottling and discolouration of the leaves (hence its name). Normally TMV in euphorbias has little effect on the growth of the plant, aside from the typically discoloured or sometimes distorted leaves, and the plants can survive a long time. As the plant sap contains the infectious virus, there is a danger of passing it to other plants, and so infected plants are best removed from the collection.
This is a name given to various pests which can be found on euphorbias. The adults, which are about 1.5 mm and look like tiny flour-covered moths, and the yellow-green larvae, 0.3-0.7 mm long, prefer the under-side of leaves, the adults usually occupying the upper leaves and the larvae more mature plant parts. They suck plant sap and excrete honey dew which can lead to black mould. In serious infestations the plant can turn yellow and dry back.
Infected plants should be isolated where possible and must be treated. Yellow sticky strips can be used to catch the adults, but it will also be necessary to spray at least 4 times at 5-10 day intervals with pyrethrum, soft soap or insecticide (including systemic). A leaf-shine spray also helps against the larvae. As the eggs are unaffected by these methods, repeat sprays will be necessary.
White fly can also be dealt with biologically with the parasitic wasp, Encarsia formosa.
www.euphorbia-international.org
