How to Control Weeds

Taraxacum officinale

The most effective way to inhibit weeds is to plant something in their place. Weeds will grow on any open ground. But most weed seeds will not sprout on densely shaded ground. The best plants to shade the ground are groundcovers, shrubs & spreading perennials. Weeds are less of a problem in shade. But seeds will still sprout on lightly shaded open ground.

I don’t want to discourage you. But there will always be weeds. You must be vigilant: Pull weeds before they set seed! Weeds come from seeds. Plastic, rocks, gravel & bark will not keep weeds away forever. Weeds mostly seed in from above. Bark & other mulch will help to keep weeds under control for a time, while other plants have a chance to get established. Be sure you can distinguish weeds from the groundcovers you have planted.

To get rid of weeds that already exist, you should probably just pull them out. It will help if you loosen the soil with a garden fork, hoe or hook. Don’t be fooled into thinking that is the end of the weeds. There are undoubtedly still seeds in the ground. Keep watching for new weed sprouts.

Weeds with long, fleshy roots (like dandelion & bindweed) will grow back, if part of the root is left in the ground. This is also true for blackberry. It can be very difficult to get all of the roots of a blackberry vine. If it grows back, keep cutting it off at ground level. I don’t think that herbicide is any more effective than cutting.

Groundcovers for Shade

 Dicentra formosa April 2009

 Achlys triphylla May 2009

Smilacina stellata May 2009

Oxalis oregana April 2009

Here is a list of groundcovers  that grow in shade for garden in Seattle, the Pacific Northwest & USDA Zone 8.  Generally, groundcovers are perennials that spread over the ground by one means or another. Groundcovers are very helpful to control weeds. They give depth & richness to a garden. They make plantings look more natural. Choose several groundcovers if your garden is small, many if your garden is large. A single groundcover will spread throughout, looking a bit weedy. As in business, it is better to give groundcovers competition than to let them monopolize your garden. You will also get better coverage & weed-suppression by using a variety of groundcovers.  The groundcovers pictured above are all Pacific Northwest native plants.  Many sources of information will tell you they require moist shade.  But these will all survive the summer with very little irrigation.  I've seen Achlys triphylla growing luxuriantly in dry Ponderosa Pine forest on the eastern slopes of the Cascade Mountains.  Although they grow in shade, do not use Hedera helix (English Ivy) or Euphorbia amygdaloides robbiae (Mrs. Robb’s Bonnet). They are too aggressive, will overwhelm other plants & grow out of control. English Ivy is considered a noxious weed by the State of Washington.

Groundcovers for Shade

Achlys triphylla (Vanilla Leaf): tolerates dryness,spreads widely, but not densely by rhizomes
Ajuga reptans (Carpet Bugle): tolerates some dryness, many cultivars, spreads by stolons & seed, also grows in sun

Alchemilla mollis (Lady’s Mantle): tolerates dryness, forms large clumps

Asarum caudatum (Wild Ginger): needs moisture, spreads by rhizomes, but not quickly

Blechnum penna-marina (Sea Plume): needs moisture, forms mats

Campanula poscharskyana (Serbian Bellflower): tolerates dryness, trails & spreads by seed

Dicentra formosa (Native Bleeding Heart): spreads widely by creeping & by seed

Fragaria vesca (Woodland Strawberry): tolerates dryness, spreads widely by runners but will share space, tasty fruits, also grows in sun

Galium odoratum (Sweet Woodruff): tolerates dryness but better with moisture, can spread widely  
Gaultheria nummularioides (Gaultheria): forms mats, needs moisture, Gaultheria procumbens (Wintergreen): spreads modestly, needs moisture

Geranium himalayense (Himalayan Cranesbill): forms spreading mats, not aggressive
Gymnocarpium dryopteris (Oak Fern): needs moisture, forms small spreading mats

Lamium maculatum 'Beacon Silver' (Dead Nettle): despite the ugly common name, a beautiful plant, forms creeping mats with limited seeding

Liriope spicata (Creeping Lily Turf): spreads widely & densely by rhizomes, will overpower other groundcovers & perennials, use under shrubs or in contained spaces

Maianthemum dilatatum (False Lily of the Valley): tolerates some dryness, spreads by rhizomes to form large patches, but will mix with other perennials
Ophiopogon planiscapus 'Nigrescens' (Black Mondo Grass): not a grass, needs moisture, spreads modestly by stolons

Oxalis oregana (Redwood Sorrel): tolerates some dryness, spreads very widely by rhizomes but willing to share space, not difficult to remove

Pachysandra terminalis: needs moisture
Phlox divaricata, Phlox stolonifera (Creeping Phlox): forms mats, needs moisture
Pleioblastus fortunei 'Variegatus' (Dwarf Whitestripe Bamboo) Pleioblastus viridistriatus (Dwarf Greenstripe Bamboo): spreads aggressively, keep in enclosed area
Polypodium glycyrrhiza (Licorice Fern): forms slowly spreading mats, also grows in trees
Sanguinaria canadensis (Bloodroot): tolerates some dryness, spreads slowly by rhizomes

Sedum forsterianum (Forster's Stonecrop): for light shade, spreads slowly

Smilacina stellata (Starry False Solomon's Seal): tolerates some dryness, spreads by rhizome to form large patches, but will mix with other perennials

Soleirolia soleirolii (Baby’s Tears): needs moisture

Tellima grandiflora (Fringecup)

Vinca minor (Dwarf Periwinkle): spreads aggressively by creeping & rooting stems, not for small gardens

Groundcovers for Sun

  Arctostaphylos uva-ursi February 2010

Veronica pectinata April 2009

Geranium orientalitibeticum May 2009

 Sedum reflexum February 2010

Thymus pseudolanuginosus February 2010

Here is a list of groundcovers  that grow in sun for garden in Seattle, the Pacific Northwest & USDA Zone 8.  Generally, groundcovers are perennials that spread over the ground by one means or another. The exceptions here are some woody trailing or vining plants & some low spreading shrubs. Groundcovers are very helpful to control weeds. They give depth & richness to a garden. They make plantings look more natural. Choose several groundcovers if your garden is small, many if your garden is large. A single groundcover will spread throughout, looking a bit weedy. As in business, it is better to give groundcovers competition than to let them monopolize your garden. You will also get better coverage & weed-suppression by using a variety of groundcovers. Most of the groundcovers listed below tolerate dryness. Xeric plants prefer dryness & often require well-drained soil.

Groundcovers for Sun

Acaena microphylla (New Zealand Burr): xeric, spreads widely, can overwhelm smaller perennials, often used between stepping stones
Achillea millefolium (Yarrow): xeric, forms spreading mats

Ajuga reptans (Carpet Bugle): many cultivars, spreads by stolons & seed, also grows in shade, shares space well

Arctostaphylos x media (A columbiana x A uva-ursi) Arctostaphylos nevadensis (Pinemat Manzanita) Arctostaphylos uva-ursi (Kinnikinnick): all xeric, spread by prostrate branches, can be controlled by pruning

Armeria maritima (Thrift): xeric, forms small mats, easy to remove
Aubrieta deltoidea (Rock Cress): forms mats, spreads by seed
Aurinia saxatilis (Basket of Gold): xeric, forms low mounds, spreads by seed

Campanula carpatica (Carpathian Harebell): forms slowly spreading mounds
Ceanothus gloriosus (Point Reyes Ceanothus) Ceanothus griseus var. horizontalis (Carmel Creeper): xeric, low spreading shrubs, can be contained by pruning

Cerastium tomentosum (Snow in Summer): forms small mats, short-lived
Chamaemelum nobile (Roman Chamomile): tolerates some dryness, can spread invasively by seed, this is not used for tea
Erica x darleyensis (Darley Heath): low spreading shrub

Erigeron glaucus (Beach Aster): xeric, forms mats with limited spread, Erica karvinskianus (Santa Barbara Daisy): xeric, short-lived, but returns & spreads by seed
Euonymus fortunei 'Coloratus', Euonymus fortunei 'Emerald Gaiety' (Winter Creeper): low spreading shrub, tolerates dryness

Euphorbia cyparissias (Cypress Spurge): xeric, spreads widely by rhizomes & seed, can be invasive, Euphorbia myrsinites (Myrtle Spurge): xeric, forms prostrate clumps, spreads by seed
Fragaria chiloensis (Sand Strawberry): tolerates dryness, spreads by runners, little fruit, Fragaria 'Pink Panda': spreads by runners, no fruit, Fragaria vesca (Woodland Strawberry): spreads widely by runners, but will share space, tasty fruits, also grows in shade

Geranium x cantabrigiense (Dwarf Cranesbill): forms mats, tolerates dryness, Geranium orientalitibeticum (Tibetan Cranesbill): forms small patches, tolerates dryness
Hebe glaucophylla, Hebe x pimeleoides, Hebe pinguifolia 'Pagei' (Hebe): low shrubs with limited spread, tolerate dryness

Hypericum cerastioides (St John’s Wort): forms mats, spreads from seed, easy to control
Iberis sempervirens (Evergreen Candytuft): tolerates dryness, spreads moderately to form mounds

Juniperus conferta (Shore Juniper) Juniperus procumbens (Japanese Garden Juniper) Juniperus squamata 'Blue Carpet': tolerates dryness, shrubs form mats with prostrate branches, can be controlled by pruning
Leptinella squalida (New Zealand Brass Buttons, formerly Cotula): needs moisture, spreads widely, can overwhelm smaller perennials, often used between stepping stones

Lithodora diffusa (Lithodora): xeric, sprawls modestly
Penstemon pinifolius (Pineleaf Beardtongue): xeric, low spreading shrub

Pratia pedunculata (Blue Star Creeper, formerly Laurentia fluviatilis): tolerates dryness, spreads widely, but shares space fairly well, may prevent some bulbs from emerging
Rosmarinus officinalis ‘Prostratus’ (Trailing Rosemary): xeric, low spreading shrub

Sedum oreganum, Sedum reflexum 'Angelina', Sedum spathulifolium 'Cape Blanco', Sedum spurium (Stonecrop): xeric, spreads by rooting stems, many species & cultivars

Stachys byzantina (Lamb’s Ears): xeric, spreads widely by rooting stems & seed, but easy to remove

Thymus serpyllum (Creeping Thyme) Thymus pseudolanuginosus (Woolly Thyme): xeric, forms very low mats
Trachelospermum asiaticum (Japanese Star Jasmine): vining stems spread densely to 20 feet, use under shrubs, not with perennials

Veronica pectinata (Woolly Speedwell): xeric, spreads very widely, but not terribly difficult to remove, Veronica prostrata (Harebell Speedwell): xeric, spreads widely, Veronica repens (Creeping Speedwell): xeric, spreads modestly

Rototilling Weeds

Here is a question sent to me in June 2009 about rototilling weeds.

Question:
We're starting to get serious about landscaping our backyard. Time and money have been the main reasons we've been unable to since we moved in. Since we've moved in, the area has been taken over by weeds. I tried to work on removing them, but it's turning out to be a lot of back breaking work!!! I went to home depot and they notified me that rototilling it would be my best bet. but they mentioned to rototill the area, and then leave whatever's been tilled there, including the weeds. I understand that this will turn into a good compost for the ground? If we have plans to eventually lay out patio blocks for a sitting area, should I keep the tillings there still? And for the areas that we'd like to just have rocks, or maybe bark, should we also leave them there? As you can tell, I'm pretty novice to this, so any advice would be greatly appreciated.

Answer:
It may take a while for you to control your weeds. You need to remove the roots from the area you have rototilled. Many weeds can regenerate from just a small piece of root. If the weeds have set & dispersed seeds, which they probably have, you will have many new weeds growing in the area. Rototilling will not destroy weed seeds, it will merely move them around. You will have to pull weeds, by 1 means or another, for 6 months or a year. Weeds do not make good compost because they are full of seeds.

If you lay out blocks for a patio, you will likely have weeds growing in the cracks. These will come both from seeds remaining from the rototilling & from new seeds blowing in from the surrounding area. Rototilled ground is loose & will settle. It is much better to lay paving materials on hard-packed earth. Otherwise, your blocks will sink over time, settling unevenly. It would be better to scrape off the top layer of soil with the weeds in it, or pull the weeds. If you have particularly pernicious weeds in your yard, like blackberry, don't pave over them. They have deep & extensive roots. They will definitely come up through the paving.

I'm sorry to tell you that weeding is forever, even in areas with bark or rocks, although bark does help for awhile. The best defense against weeds is to plant shrubs & groundcovers. Most weed seeds will not sprout on densely shaded ground.