When it comes to the soil needs, a well-draining, rich organic soil is ideal for a Philodendron Subhastatum plant. It should be a mixture of loam, sand, and peat, all in equal portions. You can also use compost as a soil amendment. A soil with slightly acidic to slightly alkaline pH (5-8) is preferred. Make sure that the soil is well-drained and does not hold water.