How often do I use potash in my garden? I know not to use it on hydrangeas and azaleas etc. But last winter I had some shrubs that should have flowered that didn't e.g. my snowball tree and a viburnum. Both are healthy and facing south.

Hi Helen, being on the south side of the house does the viburnum get enough sun? Like a rose, to initiate flowering it requires at least six hours of sun per day, if there isn’t enough sun then flowering will be reduced. Viburnum like slightly acid soil conditions like azaleas, camellias, rhododendrons so put a mulch of pine needles around the base or use Tui Peat Plus as a mulch, peat has slightly acid soil properties.

Apply a balanced fertiliser for acid loving plants such as Tui Acid Food or Tui Enrich Rose, Camellia, Azalea & Gardenia triple action fertiliser.

Avoid pruning the tree unless it is growing somewhere that is unwanted. If pruning is required then prune straight after flowering as any later than that will remove flowering wood for next season. Keep soil moisture constant, don’t let it dry out over the summer months by applying mulch to keep the soil moist. Tui Mulch & Feed is ideal, or Tui Peat Plus.

By just applying Sulphate of Potash you could be causing an imbalance in the soil, over application of fertiliser can be as bad as not applying fertiliser at all. If the balance is out then it affects nutrient uptake of the plant. The only way to truly know what the soil needs is by using a soil test kit. We believe it is other factors (environmental) that are leading to the tree not flowering, not a lack of Sulphate of Potash.