Weeds and Weeding Houseplants And Window Boxes

Weeds can be as annoying in window boxes and tubs as in the open garden, and even house plants may need weeding from time to time. Here’s how to do it effectively.

A weed is a plant growing in the wrong place: usually a wild plant that prefers the comforts of a well tended garden. Weeds may be more difficult to get rid of in lawns, flower beds and borders, because of the large numbers involved, but they can still be a problem in window boxes and tubs on patios, and even in flower pots indoors. Weeds look unattractive. They also carry pests and diseases that can spread to your plants, and take their food, water, space and light. Because most weeds are strong and tough, they often smother the plants you are so carefully trying to grow.


The first way to control weeds is never to use soil straight from the garden in flower pots, tubs or window boxes. Even though you can’t usually see them, the soil is likely to contain seeds of annual weeks, such as Chickweed or Groundsel, and of perennial weeds, such as Dock or Creeping Thistle. Garden soil may also contain tiny bits of root or underground stems of perennial weeds, such as Couch Grass, each piece of which can grow into a complete plant!

Hand weeding is best

If weeds appear, remove them by hand straight away. Use a kitchen fork, hand fork or trowel to lever up the roots, holding the weed stem or stems as close to the potting mixture as possible. You may have to follow a root some distance into the potting mixture to get it all out, but, especially with perennial weeds, this is very important. Just cutting off the top growth may encourage the weed to grow even stronger!

  • Always remove weeds before they flower and set seed, to prevent new weeds from growing. Never leave bits of them on the surface of the potting mixture, as many will simply send out new roots.
  • To remove deep-rooted weeds, gently ease the plant from the pot sideways Tease out the potting mixture and gently pull the weeds out.
  • Outdoors, remember to weed around the base of a tub or flower pot, where potting mixture or debris often collects. And if you disturb the roots of a patio or window box plant when pulling out weeds, carefully firm it down and water it in afterwards.


Outdoors, covering the surface of potting mixture with a mulch helps prevent weeds and looks attractive. Wood bark chips, gravel or granite chippings and peat are all suitable. Remove any weeds before you mulch and, if the weather is dry, give the plant a good watering first.

  • Algae, moss and liverworts Green slime, or algae, sometimes grows on the outside of clay flower pots. Though not actually a weed, algae looks unattractive and unclean.
  • Algae on a clay pot is usually a sign of a blocked drainage hole or overwatering, so you should also check the drainage hole, and repot the plant if necessary.
  • Use a stiff brush and soapy water to scrub off the algae on the pot.


If I cannot use the soil straight from the garden, why are soil-based potting mixtures alright?

These are steam or chemically sterilised before lime, sand and fertilisers are added, so any weeds and weed seeds are killed.

I have tried to weed out Couch Grass from a tub with a rose bush in it, but the more I weed, the more Couch Grass appears. What can I do?

You can use a weedkiller, such as dalapon or alloxydim sodium, especially made to kill perennial grass weeds. Or dig the rose up in winter while it is resting, and remove every trace of Couch Grass from its roots. Replant in fresh potting mixture.

I used potting mixture in my window box, but weeds are star ing to grow. Where did they come from?

Weed seeds can be carried by the wind or spread by bird droppings. There might have been weeds or weed seeds in the rootballs of your window box plants. Wherever they came from, remove them as soon as possible.



  • Try hand weeding first.
  • If you use a chemical weedkiller, read the label carefully.
  • Use a chemical only for the purpose intended and at the strength stated.
  • Use gloves when applying a chemical and thoroughly wash your hands after use: Call a doctor if any gets in your eyes or mouth.


  • Store chemicals within reach of children and pets.
  • Store chemicals in containers other than the ones in which they were sold.
  • Use chemicals outdoors on windy days, when they may drift to other plants, or on sunny days, when they can scorch leaves.

What to look for

Moss and liverworts – tiny, nonflowering plants with flat, small leaves – sometimes grow on the surface of potting mixtures. Mosses and liverworts don’t harm mature house or patio plants, though they could smother tiny seedlings in a seed tray or propagator. Like algae, they are a sign of poor drainage or compacted potting mixture.

Using a fork, gently scrape off the moss and liverworts, being careful not to disturb surface roots. Top up with fresh potting mixture, if necessary. Try to replant in fresh potting mixture when the time is right.

Unexpected weeds

Sometimes house plants themselves can become weeds, especially in a warm, damp greenhouse. If a tiny piece of Mind Your Own Business falls on bare potting mixture, it will quickly send down roots and form a new plant that completely covers the potting mixture. Some fern-like Selaginellas do the same thing, and even Maidenhair Ferns have been known to get out of control! Luckily, these plants won’t cause trouble in a dry room indoors.

Mosses and liverworts can smother little seedlings and they must be removed. Their appearance indicates poor drainage or compacted soil.

And the built-in applicators, such as fabric wicks or brushes, mean you never touch the weedkiller itself. You apply the liquid or glyphosate gel directly on to a weed leaf, and as the poison is taken into the plant so the entire weed, including its roots, dies. Although these products are more expensive than other types, you only need small amounts and nothing is wasted.

Chemical weedkillers

Chemical weedkillers are effective, bur if you use them carelessly, they can burn and scorch leaves and stunt or even kill house and patio plants. They can also be very dangerous to wildlife, household pets and people!

Best for tubs, window boxes and flower pots are the prediluted weedkillers in small spray guns or cannisters. You don’t have to measure or mix anything.

Sorry, comments are closed for this post.