Grevillea juniperina

Cultivation:

Grevillea juniperina is best planted in spring, after the last frost. It prefers soil with an acidic to neutral pH, sandy, loamy, or poor and very well-drained. The presence of limestone in the soil causes yellowing of the foliage, chlorosis, which weakens the bush until it eventually dies. This condition can be corrected by regular application of iron in its chelated form (sequestrene). In regions where the soil and subsoil are limestone, it is advisable to dig a large hole of 60 cm (23.6 in) in all directions, filled with ericaceous soil or compost and non-limestone sand. Growing in pots allows for better control of the substrate and allows the plant to be stored frost-free in a borderline hardiness zone (down to -10/-11°C (14/12.2 °F) for a well-established plant).

Grevilleas are drought-resistant plants once established: monitor watering during the first 2 summers, this will become optional or even unnecessary later on. In the ground, they appreciate a thick layer of mulch. Use wood chips or grass clippings. It is advisable to use a fertilizer very low in phosphorus, as it can reduce the plant's drought resistance by destroying the dense root hairs that develop just below the soil surface. A fertilizer with an N-P-K ratio of 18-2-10 is well suited.

For pots choose Grevillea species and varieties with low development. Use a light, well-drained potting mix that stays moist. We recommend the following mix: 60% pine bark, 20% coarse river sand, 10% fine river sand, and 10% clay soil for its water retention capacity. The pH should be 7 or less.

Insects and diseases:

Grevilleas can develop black leaf spots, caused by a rarely fatal fungus: a fungicidal treatment will take care of it.

Collar rot can also be observed, a deadly disease, also caused by fungi that develop in moist and warm soil. Avoid burying the plant's collar, which should be exposed to air. Avoid watering too often in hot and dry weather, let the soil dry out between waterings.

Phytophthora (cinnamomi), a disease also caused by a fungus, affects many plants in dry areas. The parasite destroys the roots during excessively rainy winters. The plant can suddenly wither in summer due to lack of water as a result of the destruction of part or all of its roots. Partial or complete death of the vegetation or branches can be observed in severe cases. Prevention is crucial because the disease is almost impossible to eradicate: ensure that the soil drainage is perfect, remove the water from the saucer placed under the pots, and eliminate dead or diseased parts.

Pruning:

Grevilleas tolerate annual pruning well, during their growth period or just after flowering. Shorten the branches by one-third of their length. A regularly pruned bush will be more branched and more floriferous.

Propagation: by spring sowing, or cuttings taken with a heel in June-July. To improve the germination rate of fresh seeds, they can be immersed in boiling water.

Regarding sowing: Grevilleas are plants linked to fire ecology: as such, they produce seeds that often need the action of intense and brief heat to break their dormancy.