Grevillea gracilis Clearview David

Cultivation:

Grevillea is best planted in spring, after the last frosts. It prefers soil with an acidic to neutral pH, sandy, clayey, 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 dies. This condition can be corrected by regular application of iron in its chelated form (sequestrant). In regions where the soil and subsoil are limestone, it is advisable to dig a large hole 60 cm (23.6 in) in all directions, filled with ericaceous soil or compost and non-limestone sand. Growing in pots allows 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 well established: monitor watering in summer for the first 2 summers, but watering will become optional or even unnecessary afterwards. In open ground, they appreciate a thick layer of mulch. Use wood chips or lawn clippings. It is recommended to use a fertilizer very low in phosphorus, as it can decrease the plant's resistance to drought by destroying the thick root hairs that develop just below the soil surface. An N-P-K fertilizer with proportions of 18-2-10 is well-suited.

For pots, choose Grevillea species and varieties with low growth. Use a light, well-drained but still moist potting soil. 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 lower.

Insects and diseases:

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

They can also succumb to collar rot, 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 in 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. It will cause the death of a part of the vegetation, or the entire branch in severe cases. Prevention is crucial, as the disease is almost impossible to eradicate: ensure that the soil drainage is perfect, remove excess water from the saucer placed under the pots, and remove 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 by taking cuttings with heels 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, so they often produce seeds that need the action of intense and brief heat to break their dormancy.