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Some plants only need the right outdoor environment to make seedlings for you.
Propagate Plants Naturally, Without the Fuss
August 29, 2001 by Evelyn J. Hadden

If you have no interest or time for growing plants from seed indoors, you can still grow low-cost seedlings for your garden with very little effort. All you need are a few seed-producing plants and a bed of gravel; Father Time and Mother Nature will supply the seedlings.

The Discovery

The gravel seed bed method has been used for eons. I discovered it by accident when I made a gravel path through a damp, shady area of my garden. Two months later, I noticed seedlings of nearby columbine (Aquilegia hybrida 'Nora Barlow') and forget-me-not (Myosotis sylvatica 'Blue Bird') growing in the gravel path.

I scooped the seedlings out with a shovel, gravel and all, and moved them to the planted areas. I watered them every so often during the next month but otherwise didn't pay much attention.

Some didn't make it, but many did. I'd done very little work and had many new plants to show for it!

Since then, I've rescued and replanted well over a hundred seedlings from gravel beds around my property. With them I've filled out planted areas for free, with little work, and with an impressive success rate despite lackadaisical aftercare.

Creating Gravel Beds

You don't have to set aside a special area for a gravel seed bed, though you could if you have the space. A separate "nursery room" for seedlings could be hidden from visitors and would keep things more tidy, which might help you relax in the garden if you're the kind of gardener who's always noticing what has to be done next.

Since I garden in a small urban lot where every square foot counts, I've created gravel paths and patios that double as seed beds. These fit the informal look of my garden, and I don't mind green patches among the stepping stones. I also find it convenient to grow my seedlings near the beds into which they'll be moved.

Sprinkle some soil in your gravel to encourage seedlings. My seedlings have done much better in "dirty" gravel because the roots feed on it and it holds water.

When to Transplant Seedlings
  • Size: You'll probably need to learn by trial and error the right size for transplanting each species.
    • I try to move most seedlings when their basal rosette is two to three inches in diameter, but this will vary according to the growth habits of the particular species.

    • Seedlings will usually transplant well if they are large enough to have formed a root ball. I tug one seedling first to check its resistance... if it comes right out, it's probably too small. If it looks top-heavy—the leafy part is much larger than the roots—then it's also likely too small to move successfully.

    • For those that do not form basal rosettes, I have to guess. Golden Hops vine (Humulus lupulus 'Aurea') seedlings, for instance, need to be no more than a foot long aboveground; if I wait until they're longer, their roots are too large to dig easily.

  • Scarcity: My technique also depends on how many seedlings a certain species produces.
    • Seedlings from prolific self-sowers get moved when they are quite young, but as these tend to grow in clusters, I often move a whole cluster of seedlings at once, which minimizes damage to their roots.

    • For less common seedlings, the smaller the rootball, the more careful I am. I prefer to wait until there are a handful of roots rather than just a few sparse strands.

    • If it's a rare seedling that I want to preserve, I'm even more cautious and let it grow larger.

  • How to Transplant Seedlings

    If they're moving to bare soil, I use the technique my grandmother taught me:
    1. scoop out a shallow hole,
    2. add enough water to create squishy ground,
    3. place the gravel and seedlings gently on the (muddy) surface,
    4. sprinkle the scooped out soil back over their roots but leave stems and leaves uncovered, then
    5. pat down firmly (with gloved hands or rubber-booted feet, if you want to stay dry).
    To transplant to mulch-covered beds, don't place plants on top of the mulch. Push away the mulch layer to reveal soil, then plant into the soil. If the soil is covered with many inches of mulch, you can raise the level of the soil in the planting hole by removing a shovel full of soil and filling the hole with mulch, then replace the soil over the top of the mulch and plant seedlings in soil.

    If the seedlings are moisture-loving (i.e. came from the moist side of the house), I usually spread a one-fourth to one-half inch layer of wood chips around their bases after transplanting. This deters weed seeds in the soil from germinating and competing with the little plants, and it also keeps their fragile roots moister and cooler. If the seedlings are moving from dry sandy beds, I usually top them off with a similar depth of sand or gravel, which will protect their roots but preserve good drainage.

    Whether they germinated in a wet or dry area, I make sure each plant is thoroughly watered after planting and mulching. I hang the end of the hose a couple of inches above the ground and water in a circle around the plant's center, until the ground around it is squishy, stopping before the plant starts swimming. If the plant starts to float, I take away the water and push the plant down firmly with my foot to reseat it.

    I soak new transplants in this way every few days for the next couple of weeks, more often if I notice they're extremely dry and less often if we get a good rain. After that, I only water in periods of drought, which is roughly two-and-a-half weeks without rain in these parts.

    Seed Sources

    My "seed plants" are planted in beds adjacent to the gravel areas. You could also plant a few seed plants directly into the gravel. (Actually, you'd want to plant them in the soil under the gravel, then water them enough to make sure they establish well and produce a large crop of seeds.)

    If I couldn't find seed plants or didn't want to pay for them, I'd buy a packet of seeds and scatter them on the gravel. I'd try to pay attention to when they'd normally release their seeds, and I'd scatter mine at that time of year.

    More realistically, I might just scatter them when I'd bought them, then if they didn't grow, try again with a new packet giving more consideration to when they should be scattered. I would not, however, scatter them before the last spring frost or within a month of the first fall frost unless the seed packet or catalog instructed me to do so.

    Many of my plants originally came from seeds sold by Thompson and Morgan, and most were labeled "Easy to Germinate" in their catalog.

    Surprising Seedlings

    Many cultivated varieties (cultivars) don't come true from seed; that is, they produce seedlings of the species rather than the cultivar; these new plants vary from their parent in flower color and shape, leaf color, and other characteristics. Others cannot reproduce by seed.

    I've seen several different results from seed propagation. My butterfly bush (Buddleja davidii 'Black Knight') produced several seedlings, all of which had the light purple flowers of the species rather than the striking dark purple blooms of that variety. On the other hand, my columbine (Aquilegia hybrida 'Nora Barlow') produced many seedlings, all of which carried the same blue-green leaves and spurless, yellow and red flowers of that variety. Every so often, one of the seedlings from my Musk Mallow (Malva moschata alba 'Pirouette') sports a white center instead of the parent plant's light pink centers.

    Encouraging your plants to self-sow can add a new dimension of mystery and anticipation to your gardening experience. If you like surprises, it can be fun to watch what new plants your existing plants produce.

    Gravel Maintenance

    My gravel beds were between three and four inches deep when I first laid them. After four or five "harvests", I added another inch of gravel in places where seedlings commonly sprout. Before that, I merely smoothed out the surface of the gravel after digging up seedlings, which slightly lowered the surface of nearby areas but otherwise erased any traces of disturbance.

    Clearing the gravel paths and patios of seedlings in spring and fall coincides nicely with good replanting times for many species. My main seedling crop is forget-me-nots, which I need to replenish often as they're biennial and thus tend to disappear after two years, so I schedule my digging based on their calendar. I usually "harvest" seedlings in early spring after the ground thaws but before the forget-me-nots bloom, then again in mid-fall after the summer-sown seedlings have grown large enough to transplant but before fear of frost would keep me from moving them.

    However, I don't stick to a firm schedule, and I've been known to dig up a seedling that brushed my bare toes once too often and plunk it into its permanent destination, disregarding the date.

    To Stop Propagation

    If you decide you no longer want to encourage seedlings, you'll need to replace the gravel with some other medium. There are a couple of ways to do this:
    1. Remove the gravel. Scoop it up and sprinkle it through your planting beds. It will aerate the soil. One caution, however: lime sand or limestone gravel have very high alkalinity, and acid-loving plants will not appreciate even a small dose of lime, so steer clear of acidic planting areas when you're dispersing these materials. Replace the gravel with a material less conducive to self-sowing, such as a several-inch layer of firmly packed wood chips.

    2. Don't remove the gravel. If you don't mind raising the level of the gravel area, there's no need to remove the gravel before adding wood chips; add a several-inch layer and pack them down over the top of the gravel.

    Plant Lists

    In my zone 4 garden, I use several gravel beds that have different environmental conditions. I have been able to encourage many species to self-sow in each. Here's a brief list for each area:
  • Dry Acidic Afternoon Sun: The front patio, with rock pavers set on limestone sand under a spreading pine tree, gets southwest sun. Plants that have seeded in the cracks between patio pavers include :
    • Jack Pine (Pinus banksiana)
    • Brown-eyed Susan (Rudbeckia fulgida and R. f. 'Goldsturm')
    • Pale Yellow Coneflower (Ratibida pinnata)
    • Coreopsis (C. lancelota)
    • Butterfly Bush (Buddleja davidii 'Black Knight')
    • Lavendar (Lavandula officinalis 'Munstead')
    • Bachelor's Buttons (Centaurea montana)

  • Damp Mostly Shade: The narrow path of river rock pea gravel runs along the damp, mostly shady eastern side of the house. Plants that have seeded in the path include:
    • Violets (Viola sp.)
    • Forget-me-nots (Myosotis sylvatica 'Blue Bird')
    • Columbine (Aquilegia hybrida 'Nora Barlow')
    • Golden Hops (Humulus lupulus 'Aurea')
    • Musk Mallow (Malva moschata alba 'Pirouette' and M. m. rosea)
    • Lady's Smock (Cardamine pratensis)
    • infrequent Coral Bells (Heuchera micrantha 'Chocolate Ruffles' and H. m. var. diversifolia 'Palace Purple')
    • infrequent Lady's Mantle (Alchemilla mollis 'Thriller')

  • Limey Full Sun: The limestone sand bed bakes in the dry, sunny back corner.
    • Garden Sage (Salvia officinalis)
    • Swamp Milkweed (Asclepias incarnata)
    • Aster (Aster sp.)
    • Yellow Nutsedge (Cyperus esculentus)
  • Not every plant will propagate in gravel, but I suspect that many more than these will, given encouragement, produce enough extra plants that you can save significant money and energy.

    So if you're sick of the indoor potting rituals, why not take a break? Set up a gravel seed bed, then relax in your garden while Nature and Time supply you with seedlings.

    For More Information:

    Lewis Hill wrote the best book I've found on propagation. The diagrams hardly need text, they're so self-explanatory.

    Related LessLawn articles:

    make a gravel path

    make a gravel patio

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