Key Takeaways
- Planting into gravel works when the roots finish in real soil under the stone, so the gravel is scraped aside, the plant is dug into the ground, and the stone is raked back afterwards.
- Plants set into a gravel layer alone, with no soil beneath, dry out and die in the first hot spell.
- A cross cut in weed membrane, just large enough for the rootball, lets a plant go through existing fabric without removing it.
- A gravel bed needs about 5 to 7.5cm of stone around the plants once they are in, deep enough to keep weed seed in the dark but shallow enough that small plants show.
- A gravel mulch holds the ground dry at the collar of a plant, so lavender, cistus and other grey-leaved plants last longer in stone than they do in bark.
- A planting pocket dug into heavy clay fills with water and rots the roots, so on clay the bed is built up above ground level rather than dug into it.
One job I had about ten years ago, back before I started Outdoor Aggregates, a client wanted to upgrade a fairly tired gravel front garden without ripping the whole thing out. I told her that was usually pretty easy, so we started by moving some gravel aside to see what we were dealing with. About 5cm down, I hit landscape fabric in fairly good nick, and underneath that was more gravel of a different type, before we eventually reached the old topsoil. It’s a fairly common situation with gravel gardens: from the surface, you can’t tell whether you’ve got decent planting ground or several layers to get through to reach soil. In this case, I cut into the membrane where she wanted the plants, cleared out the excess gravel and opened up proper planting holes before adding compost, new plants and raking back the gravel and topping up with some fresh stuff. The garden looked just renovated without having to strip the whole area. Always dig one test hole first as it can save a lot of unnecessary work later.
Can You Plant Directly Into Gravel?
Planting directly into gravel works provided the roots finish in the soil beneath the stone, because gravel by itself holds neither water nor food. A plant whose rootball sits in the gravel layer gets through a wet spring and dies in the first dry fortnight of summer. So the stone is moved aside, the plant goes into the ground below, and the gravel goes back around it as a mulch.
Gravel is a good place to plant for the same reason. The stone stays dry at the collar, where rot gets in over a wet winter, while the ground underneath stays damp. That is why the Mediterranean plants people want in a gravel garden, the lavenders, cistus and cotton lavender, do better sitting in stone than they ever do in a bark mulch. The beds where bark is the better cover are set against stone in rocks in landscaping.
How to Plant Into Gravel in Seven Steps
The method below covers a new bed and existing gravel alike. Only step one and step two change with what you find under the stone, and the table after the steps deals with that.
- Dig a test hole. Scrape the gravel back in one spot and dig down a spade’s depth. You are looking for four things: how deep the stone goes, whether there is a membrane, whether there is hardcore under it, and what the soil is like when you get there. Squeeze a damp handful. If it rolls up sticky, like plasticine, you are on clay and the clay section below applies. If you are not sure, a soil texture jar test settles it.
- Scrape back and open up. Clear the gravel from a circle about twice the width of the pot, down to whatever is underneath. If that is weed membrane, cut a cross in it just big enough to take the rootball. Pull out every scrap of perennial weed root you find, bindweed and couch grass especially, because gravel will not stop them coming back through. On a new bed, dig the whole area over and mix in grit if the soil is heavy.
- Soak the pot. Stand each plant in a bucket of water for an hour or two before it goes in, until the bubbles stop. Gravel garden plants are drought tolerant once established. In the pot they are as thirsty as anything else, and a dry rootball planted into free-draining ground stays dry.
- Plant into the soil. Dig the hole so the top of the rootball sits level with the soil surface. Not buried, not proud. On a bed where the gravel is deep, set the plant on a slight mound so it finishes a touch above the stone rather than swamped by it. Tease the roots out if they are circling.
- Firm in and water. Push the soil back round the roots and firm it with your hands so there are no air pockets, then water it in properly. A watering can is fine. A dribble from the hose is not.
- Close the membrane and draw the gravel back. Fold the membrane flaps back under the stone so the cut is covered, then draw the gravel back to 5 to 7.5cm, right up to the neck of the plant. The stone keeps the collar dry, and the collar is where rot starts.
- Water through the first summer. A plant sold as drought tolerant only becomes one once its roots are out in the ground, and that takes a growing season. Through the first summer, water anything that wilts, and do not feed. Rich soil and fertiliser give these plants soft growth that flops in the heat.
What Is Under Your Gravel?
Step one tells you which of these you are dealing with. Every one of them can be planted. The work varies from ten minutes to a morning.
| What you find | Can you plant? | What to do first |
|---|---|---|
| — | — | — |
| Gravel on soil | Yes, straight in | Scrape the stone back and plant into the ground |
| Gravel on weed membrane | Yes, through a cut | Cut a cross the size of the rootball, plant through it, fold the flaps back |
| Gravel on plastic sheet | Yes, after removal | Cut the sheet right out around each plant, because water pools on it and the roots sit wet |
| Gravel on hardcore | Yes, with a pocket | Dig a pocket through the hardcore to soil and fill it with topsoil before planting |
| Gravel on clay | Yes, built up | Do not dig a pocket into the clay. Raise the bed above it, see below |
The membrane question comes up more than any other, so a word on it. Landscape fabric under gravel does a real job: it keeps the stone and the soil from mixing, and it cuts the weeding for a few years. Seed still germinates in the organic stuff that gathers among the stones, whatever sheet is underneath, and most weeds in an older bed start there. So keep it, plant through it, but don’t expect it to make the bed weed-free. Where you want verbascums and valerian to spread by seed on their own, leave the membrane out altogether, since a seedling cannot root through it.
Planting through the gravel is also a far smaller job than removing it. Clearing a whole front garden of stone and membrane runs to days, and costs a fair bit.
Planting Into Gravel on Clay Soil
A planting pocket dug into clay and filled with nice light compost becomes a bathtub. The clay holds the water in, the roots sit in it all winter, and by spring the plant is a goner. Gravel on the surface changes none of that.
What worked for me on clay was to stop digging down and go up instead. A low edge, 20 to 30cm high, of sleepers or bricks, filled with a gritty mix on top of the clay, gives the roots a free-draining root zone above the wet. Where a bed cannot be raised, the whole planting area gets grit and gravel mixed through it rather than each hole. A land drain is no use without a lower point to run to, and a flat garden rarely has one. On clay that stays wet all winter, I would plant bog plants in the ground and keep the gravel plants to a raised bed. Lavender will not last a winter sitting in water.
Plants That Grow in Gravel
Plants that grow well in gravel are the ones from dry, stony places to begin with: silver or hairy leaves that shade themselves from the sun, waxy leaves that hold water, and roots that go deep. The table has the ones I planted most and the ones that seed themselves around a gravel bed. Every one of them is planted into the soil below the stone, as above.
| Plant | Job in the bed | Self-seeds? |
|---|---|---|
| Lavender (Lavandula) | Structure and scent | No |
| Sun rose (Cistus × corbariensis) | Evergreen structure | No |
| Cotton lavender (Santolina chamaecyparissus) | Silver mounds | No |
| Creeping thyme (Thymus serpyllum) | Ground cover over the stone | Lightly |
| Silverbush (Convolvulus cneorum) | Silver leaves, white flowers | No |
| Artemisia | Silver filler | No |
| Red valerian (Centranthus ruber) | Colour on poor soil | Freely |
| Californian poppy (Eschscholzia californica) | Summer colour | Freely |
| Mexican fleabane (Erigeron karvinskianus) | Daisies in every gap | Freely |
| Miss Willmott’s ghost (Eryngium giganteum) | Silver thistle heads | Freely |
| Verbascum (Verbascum olympicum) | Height | Freely |
| Sisyrinchium (Sisyrinchium striatum) | Upright leaves | Freely |
Sun is the other half of the list. Under four hours of direct sun a day and most of these struggle, so a shaded gravel corner wants ferns and bugle (Ajuga reptans) instead. A north-facing gravel patch is a shade bed with a stone mulch, and in this case it’s best to avoid pale gravels because they will just go green in time.
Next Steps
Once the plants are in, the two things that decide how the bed looks in three years are the stone and the weeds. Outdoor Aggregates stocks the decorative gravel range in 10mm to 20mm grades for planted beds, delivered in bulk bags to the kerb, and the gravel calculator works out how many you need at 5 to 7.5cm. For the design choice between a bed that seeds itself and one that stays as drawn, and why weeds appear on top of a membrane, the low maintenance gravel garden guide covers both. If the plants you want are alpines rather than Mediterranean shrubs, the rockery plants guide is the one to read next.
If you would rather talk your gravel planting through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.
Have you ever put plants through existing gravel? What was under it when you dug, and which plants have come through their first summer? Let us know in the comments.
FAQ
Do I need a membrane under gravel if I want plants?
Weed membrane under a planted gravel bed is optional, and I leave it out wherever the plants are meant to seed themselves, because the sheet stops seedlings rooting. Under a set planting scheme that stays as drawn it earns its place, mainly by keeping the stone and the soil apart.
Can I just lay gravel on soil and plant into it?
Gravel laid straight on soil is a perfectly good planted bed, provided the perennial weeds are dug out first and the stone goes on at about 5 to 7.5cm depth. The bed will need weeding while the plants fill out, and the thin layer of debris that settles on the stone over the years is where new weeds come from.
Can plants grow in gravel without soil?
Plants cannot live in gravel alone, because the stone holds neither water nor food. Every plant in a gravel garden has its roots in soil underneath the gravel, and the stone is a mulch on top.
What size gravel is best for planting?
Gravel around 10mm sits quietly around planting and disappears as the plants fill in, which suits a small bed. 20mm holds its own against large stone, but it overpowers a small bed and swamps low, fine planting.