It is the question we get asked most, and it is usually asked apologetically — as though it were a fussy thing to care about. It is not. Mature foundation planting takes years to establish and costs real money to replace.

So here is the mechanism, properly explained, and what a competent contractor actually does about it.

How harm actually happens

House washing solution is dilute sodium hypochlorite with a surfactant. It harms plants in one specific way: absorption. Foliage takes it up through the leaf surface; roots take it up from the soil.

Which points straight at the solution. A plant that is already saturated cannot absorb much more, and soil that is already at field capacity cannot take up more liquid. Water is the antidote, and it works best applied before the problem rather than after.

That is why the professional approach leans on pre-wetting rather than on covering. Plastic sheeting has its place — directly under a heavily treated section, or over something particularly delicate — but a sheet that traps solution against foliage on a hot day can do more harm than no sheet at all.

What should happen on the day

  1. Beds are soaked with clean water until the soil will not take more. Not misted — soaked.
  2. Foliage is wetted down on anything within reach of overspray.
  3. Delicate or directly-beneath plants are covered, and uncovered as soon as that section is finished.
  4. Runoff is directed away from beds wherever the grade allows.
  5. Everything is rinsed again as each elevation is completed — not saved until the end.
  6. A final flush before the crew leaves.

If a contractor walks up to your house and starts spraying without doing step one, that tells you something.

What to tell them before they start

Contractors are not botanists and cannot tell what matters to you by looking. Worth mentioning:

  • Anything you would be upset to lose — a plant from a relative, something you have nursed for years.
  • Edible planting. Vegetable beds, herbs, fruit trees. These want covering as well as soaking, and produce directly beneath a treated wall is worth washing thoroughly afterwards.
  • Ponds and water features. Koi are considerably more sensitive than shrubs. Covering a pond is non-negotiable, and the pump is usually best switched off.
  • Newly laid sod or new planting. Establishing root systems are more vulnerable than mature ones.
  • Orchids, bromeliads and epiphytes, which absorb through their foliage far more readily than most plants.
  • Where your outdoor pets will be. Not plants, but the same conversation.

What to do afterwards

Usually nothing. If you want to be thorough, give the beds a normal watering that evening — it dilutes anything that reached the soil and it is what the plants want anyway after a warm day.

If you do see leaf damage, it typically shows within 24 to 72 hours as browning or yellowing at the leaf margins, most often on the lowest foliage. In most cases the plant recovers as new growth comes through. Water it well and give it time before deciding it has died.

The honest caveat

Done properly, plant damage is uncommon. It is not impossible.

A hot, still, dry day increases risk because solution concentrates as water evaporates. Very dense planting against a wall is harder to protect than an open bed. Some species are simply more sensitive than others.

A contractor who tells you there is zero possibility of any plant reacting is overselling. One who explains the pre-wetting sequence, asks what you care about, and says they will rinse as they go is describing the actual method — which is a much better sign.