Monday, September 25, 2017

Let's Plant! Tips for Planting and Propagating from Bulbs

Bulbs are little self-contained plant making machines. Magic! Right now, the bulbs pictured above are blooming beautifully in my spring garden. Yay! As the first post of our new Let's Plant mini-series, here's a quick into to planting and caring for bulbs in the home garden:

True bulbs like the easily recognisable onions, daffodils, and lilies are made of fleshy layers surrounding an immature internal stem and/or leaves. Other "bulbs" that aren't really true bulbs include corms, tubers, and rhizomes.  Corms, like freesias and gladioli, are solid and sometimes even woody. When you plant a corm, it is usually consumed in growing the plant and replaced with child corms at the end of the growing cycle. Stem tubers, like the potato, and root tubers, like dahlias and kumara, are thickened underground growths with growing points (aka eyes) from which new plants can grow. Rhizomes, like irises, turmeric, and ginger, are fleshy underground stems that can grow into new roots and shoots of their own.

Bulb Selection

A good healthy quality bulb will be firm to the touch and free of mould. Bulb sizes vary by species and variety, but within the same plant type, bigger bulbs will typically grow/flower more prolifically in their first planting than smaller bulbs.  The longer a bulb is stored, the lower it's probbaility of successful growth.

As with any plant, choosing varieties that you like that also suit your climate, aspect, and garden conditions will help with planting and growing success. There are bulb plants for sun and for shade, but pretty much every variety of bulb will prefer being planted in free-draining soil. Because bulb plants will naturally die back after flowering, they work well for layered plantings and adding season interest with offsetting dormant varieties of bulbs or other plantings.

Planting Your Bulbs

When you buy (or are given) new bulbs, keep the packaging label or take note of the variety and any specific planting requirements.  Store this with your bulbs until planted, as it's important to plant at the right time of year and in the best conditions for growing success.  Once planted, transfer the label to your garden journal binder or transcribe the key details in your notes so that you have then for reference.  This is especially handy for lifting, sharing, or future propagation.

Not all bulbs have the same planting cycle! Spring blooming bulbs like to be planted after summer when the weather and soil are cool. Summer blooming bulbs like to be planted in the springtime when any danger of freezing conditions has past. Some bulbs benefit from a pre-planting chill to simulate natural dormancy conditions before planting.

Prepare your planting area or container for planting.  Bulbs benefit from good quality free-draining soil as bulbs will rot in soggy soil. As noted in selection above, aspect will depend on the plant and variety, but most bulb plants prefer some sunshine for best growth and blooms.

Bulbs like to be planted to different depths depending on the type of plant. Check for your specific varieties for best results; however, a good general rule of thumb is that many (not all!) bulbs like to be planted roughly twice as deep as the bulb is tall.  Don't forget to plant them right-side-up. :)  If you can figure out which side is up by looking at the bulb (many are obvious, but some can be a bit mysterious), you can try sideways planting and keep your fingers crossed - nature often sorts itself out! If you know you're going to lift your bulbs, you can use basket-style bulb plating containers to make removal easier.  Record your bulb plantings in your garden journal and/or with plant markers so that you don't lose track of what's where when things are dormant.

Plant Care

Most bulb plants are relatively low maintenance (yay!).  For most bulb plants, good soil plus light feeding just after they sprout and again after flowering is usually plenty.  An occasional drink, general weeding, light mulching, and control of any pesky bugs and critters is about all the help most bulbs need.  If you have local animal life that might dig up bulbs, you can plant them under wire mesh to limit digging.  Snails and slugs are common pests for routine control.  Once they've finished flowering, you can (if you wish) cut the spent flower stalk but leave the leaves.  These will die down naturally once they've done their duty feeding the bulb in preparation for the next growing cycle.


Depending on where your growing climate and type of plants, you may need to lift and store your bulbs between growing seasons. If you've lifted your bulbs for seasonal storage, keep them with free air circulation in a cool dry place until its time to plant again. If you are naturalising your bulbs in situ, you can set and forget; however, lifting and splitting every few years can help improve flowering and allow you to expand your garden for free - win-win!

Bulbs can develop small offsets or bulblets (little baby bulbs) next to the root area of the bulb's basal plate. Both the bulb and the bulblets can be replanted to grow.  Similarly, corms develop a new corm or multiple cormlets (child corms) to grow the next generation. In additional to natural growth, you can expedite corm development through scaling propagation methods.

Some type of bulbs can be allowed to mature, in one cycle or multiple seasons, until they diving internally into offsets, splitting the parent bulb into clumps of internal offspring. These bulbs can be lifted and separated for replanting. Many gardeners will be familiar with this method for growing garlic (the individual cloves are offsets), but it applies to other bulb plants as well.

Some bulbs will set seed if you leave the flower stalks intact, but you may need to grow the seed significantly longer in order to develop a mature flowering plan of equivalent size to other propagation methods. We'll explore seed starting, division, and other propagation methods in our Let's Plant series.

Troubleshooting Tips

If your bulbs don't sprout when expected, review your garden journal notes on plantings and double-check that the varieties you've chosen are well suited to your climate and their planting conditions in your garden.  If everything looks good on paper but the plants haven't emerged, it may be a temporary delay so don't give up hope just yet - seasonal variations, micro climates, and other factors will affect growth. 

If your bulbs don't sprout at all and there are no obvious culprits, some further trouble shooting is needed if you want to try again for better success.  As noted above bulbs like different planting depths depending on the type of plant.  Planting too deep can cause failure to sprout and/or rotting. Too shallow and they may be overexposed to harsh conditions before sprouting.  Although you can find bulbs for a variety of different garden aspects, soggy ground is a killer.  You can try to improve poorly drained soils with sand or raise the beds, but avoid wet feet as bulbs will rot.  Bulbs planted in smaller portable pots may benefit from being placed in the shade to limit temperature fluctuations until they sprout. If the temperature of your growing climate is suited to naturalisation but your ground in the planting area has a tendency for soggy dormant seasons (like many parts of our garden during our wet wet winters) lifting may be beneficial. On the flip, if you have sizzling summers, summer dormant bulbs may benefit from lifting so that they don't roast! 

If new bulbs sprout but fail to impress with growth and/or blooms and there are no obvious issues with variety, pests, or disease, lack of chilling (such as an unusually warm winter/spring) or other adverse growing conditions (poor variety for location, low quality soil, poor aspect, over shading, etc.) may be the culprit(s).

If naturalised bulb plants were initially performing well but are declining over the years, early leaf removal (low bulb storage), decreasing soil quality, increasing shade from nearby maturing plantings, or overcrowding may be factors.  To help avoid overcrowding bulbs, you can lift and split naturalised plantings every few years as noted above. 

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