Spring Bulbs: Pests, problems, recycling
Tips and advice for overwintering potted bulbs, deterring rodents, preventing disease, dealing with slimy pests, compost mixes and FAQs
Winter protection
If your winters are relatively mild, like here in the UK where we rarely see temperatures fall below -5℃ (23℉), you can leave your potted bulbs outside all winter. Just as long as the pot and potting compost are very free draining!
However, consider tucking them against your house just because of the incessant rain! In the UK, the vast majority of winter rains blow in from the south west, so tucking those pots up against the north or east side of your house, keeps them out of the worst of any winter deluge.
Bulbs are very hardy, so no need to worry about frost, snow, or ice. They absolutely detest waterlogged soils/compost. Even when the “Beast from the East” locked the entire country in ice for weeks on end (temperatures down to -18℃ (0℉), potted bulbs in my garden were fine, because the free draining compost wasn’t waterlogged. It's the combination of a waterlogged soil that freezes solid that kills bulbs.
TIP: During the winter, my pots all sit on gravel so they can drain freely. If your pots sit on flat patio slabs, invest in pot feet, or make chocks from wood to lift them off the ground. Those pots must be able to drain. I cannot emphasise this enough!
Predators & Problems
Rummaging rodents
To keep border tulips out of reach of squirrels and other relentless rodents, plant bulbs 4x their own depth or more. I tend to plant even the smallest bulbs (crocus) at the full depth of my bulb planter and they grow and flower absolutely fine.
FUN FACT: Crocus bulbs, among others, have contractile roots and can adjust their depth! Tape here to read more!
With my bulbs all potted up and tucked around the side of the house to overwinter, out of sight, squirrels and other rodents assume those bulbs are fair game. As a deterrent, I lay metal grids or 25mm chicken wire over the pots, held in place with bricks. Simple, but effective. Once the bulbs are shooting, the squirrels seem far less interested, so I remove the guards and put the pots out on display.
TIP: Do not cover the pots with anything solid as this will reduce airflow and promote mould and fungal growth. You'll also be creating a cosy environment for slugs that will happily feast on any shallow-planted bulbs.
Killer Compost
I've read rather alarmist articles discouraging gardeners from using homemade compost for planting bulbs. "There might be all manor of nasties in there. Viruses, moulds, disease, bulb eating critters!" The list goes on. But these attention grabbers are just listing organisms that naturally occur in the ground and happily coexist with our plants. Do they imagine 'soil' to be a sterile environment? Plants are tough. Disease is thankfully rare.
I've used homemade garden compost and leafmould for years. I have never had any issue with soil-borne pests feasting on bulbs, neither are viruses or disease running rampant. If my compost is good enough to grow something I am going to eat, it's good enough for flowering bulbs.
Caveat: Do not compost diseased bulbs especially any with mould or evidence of tulip fire.
Marauding molluscs
Slugs and snails definitely have a fondness for tulips and daffodils. The spring of 2024 was incredibly wet and mild, with very low light levels. It was the absolute perfect environment for malevolent mollusc activity. For the first time ever, I found them shredding narcissus flowers - the trumpet and petals eaten to the core!
Also, at the end of the flowering season, when you've pulled the withered stems of tulips, slugs can seize the opportunity to slime their way down the hole left behind by the stem and eat the bulb. So, when you do pull out those stems, simply firm over the area with a trowel, or your boot!
Practically speaking, there's little to be done about slugs and snails, especially during such freakish springs as ’24 - in years to come it’ll be known as “The Great Slug Plague of 24!” Scattering (poison) slug pellets indiscriminately in a vain and futile attempt at protecting bulbs is a ghastly idea!
You could go out at night with a torch and collect slugs and snails in a bucket (disposing of them as you see fit - mine go onto the compost heap). But do this in Autumn before they lay their eggs and go into hiding. In pots, planters, and raised beds you could also use nematodes to reduce the slug population, but they have little effect on snails and you need to do this before soil temperatures drop below 10℃ or 50℉ .
For the garden as a whole, if you have hundreds of bulbs, all this is unrealistic. A better option is to encourage more predators like song thrush, blackbirds, starlings, frogs, toads, ground beetles, ducks, hens… (something I recently covered in more depth in my Hosta post) Last of all, let’s just hope for a cold dry winter!
Tulip Fire
Thankfully, Tulip Fire is something I have never personally experienced, so this information is from the RHS. Read the full article here.
“Tulip fire is a fungal disease of tulips caused by Botrytis tulipae, which produces brown spots and twisted, withered and distorted leaves. It is so named because in severe cases plants appear as if scorched by fire.” To avoid further spread and contaminations, the following controls should be employed:
Check bulbs carefully and discard any with signs of the small black sclerotia in the outer scales, or with any signs of decay
Remove infected bulbs promptly to avoid contaminating the soil with sclerotia
Do not plant tulips for at least three years in sites where tulip fire has occurred (five years if the disease is grey bulb rot)
If a contaminated site must be replanted, dig the ground deeply and bury the contaminated upper layers deep enough to be below planting depth
My best advice, from everything that I’ve read, is to always plant tulips with the utmost care, especially when planting in the ground. In pots, you’re usually starting off with fresh propriety compost, so Tulip Fire isn’t an issue (unless you’re replanting infected bulbs).
Assess each tulip bulb. Discard any that are soft and/or show any signs of disease or mould. Most importantly, wait until November or even December to plant tulips in the soil, when the ambient soil temperature has dropped below 10℃ or 50℉
FAQ
These questions were all gathered from my Instagram posts…
“Why do tulips flop?”
Moisture levels or a lack of sunlight, or a combination thereof. Although bulbs are tough, once in leaf they will need regular water, just like any other plant, especially so if they’re in pots. A deep weekly soaking should suffice. Tulips are phototactic and heliotropic - they physically move in response to light levels. If it’s too shady, sun-loving tulips can start leaning towards the light and the stems grow weak and etiolate, contributing to droop as they’re unable to support the comparatively heavy flower.
"Do you really have to lift and store bulbs after flowering?”
In short, no. You could leave your bulbs in their pots indefinitely. When bulbs have finished flowering, deadhead them, give them some regular seaweed feed (or Tomorite) and leave them somewhere sunny to die back naturally. Don't tie up the leaves. Bulbs need this period to recharge and regenerate. They need sunlight on those leaves. Remove the leaves only when they are all brown. When bulbs enter dormancy, they like to be dry, so position the pots out of the rain, if possible.
The only issue is that the potting compost will run out of nutrition. To combat this, you’ll need to refresh the compost. Every winter, remove the top few centimetres of old compost and replace with new. Then sprinkle over a dose of Fish-Blood-Bonemeal.
"Which compost have you achieved best results with?"
Having sampled a few over the years, the brand I return to time and again is SylvaGrow bark-based peat-free multipurpose compost. Mix this with 25% grit for added drainage and you should be off to a flier. Throw in a handful of Fish-Blood-Bonemeal slow-release for a little extra fertility - given that practically all bagged compost only has enough feed for 6-8 weeks and many bulbs are in growth for months.
“What compost (potting) mix do you use?”
My own bulb potting compost is a blend of SylvaGrow, sieved garden compost, and sieved leaf mould. The final ingredient is horticultural grit for increased drainage. I make this up in batches, in a wheelbarrow.
It’s not scientific, but it seems to work very well! Rubbing it through my fingers, I know when the overall blend is right. It shouldn’t stick together when you squeeze it in your hand. It should be very open and crumbly. Remember, for any compost mix, you need water to moisten the compost but pass through without waterlogging.
Tulips. Perennial or not?
Perennial 'species tulips' evolved in the Steppes of Persia and Himalayan foothills, where they experience baking, arid summers and freezing winters, all with sharp drainage. Dutch growers overcame these ecological necessities by mastering climate control, heat, cold, humidity, plus perfecting soils, and irrigation.
Contemporary 'border tulips' are grown on an industrial scale, specially bred and hybridised, carefully harvested at their peak, primed to survive the first winter in your garden as a fully-fuelled bulb, flowering triumphantly the following spring.
However, by the time spring has passed, the fat tulip bulb you planted in autumn has been literally emptied. All that remains are the empty scales and the emergence of a new bulb. Continued bulb and leaf growth is now powered by the established roots. Once the bloom has faded, the leaves power the continued formation of a new bulb and bulblet (aka offsets).
Bulbs are then at the mercy of our 'less than ideal' soils and climate, where winters are often ruled by rain and flood, rather than ice and snow. The diminished 'parent bulb' and tiny offsets throw up feeble leaves and an underwhelming bloom, if any. If you have cold dry winters and sandy soil you may well find tulips are perennial as it's closer to their ideal habitat.
The good news is that there are particular hybrid tulips that are recognised as being more perennial than others. Darwin Hybrids, Fosteriana, and Viridiflora are all said to be more perennial. You can also try these steps to improve your chances:
Plant tulip bulbs extra deep. In many gardens, the deeper soil is drier and the added depth seems to inhibit the creation of smaller offsets.
Avoid watering too much. Once the leaves yellow, stop watering altogether.
Avoid planting them in ground that is liable to waterlogging.
Deadhead tulips immediately as soon as the petals start to fall.
Summer warmth is good! They need warmth during dormancy as the new flower forms within the regenerated bulb.
Well drained soil warms quicker than soggy soil. Even more reason to plant in well drained soil, raised beds, or gritty sharp-draining potting compost.
Recycling spring bulbs
Option One - Lift and store
Lift the entire clump of bulbs out of their pot and repot them into a recycled plastic pot, so they can dieback naturally, in the sunshine, but out of sight. Once all the leaves have dried brown and crisp and the bulb is 'dormant', lift the bulbs, separate them, keep the largest and discard the rest. Trim off the leaves, tidy the roots without damaging the root plate, brush off any dirt and store them somewhere cool and dark but with good airflow.
Option Two - Plant out
Lift bulbs after deadheading and plant them out ‘in the green’, i.e. in full leaf in May or June. This is generally what we do now for select tulips, crocus, iris, muscari, and hyacinth.
For tulips it’s been an interesting experiment. In 2021, I planted-out all of our display tulips, in the green, into the Flower Garden borders. In Spring 2022, the vast majority of tulips returned, some just as beautiful as the year before, others significantly diminished.
Over the following two seasons, many cultivars have continued to fade away, but these ones have remained strong: Daydream, Negrita, Greenstar, White Triumphator, Sapporo, Mistress, Ballerina, Princess Irene, Angelique.
Coming up…
The Kitchen Garden! From derelict space to productive vegetable and cutting garden. I’ll share the questions posed by the oddly-shaped space: the layout, the build, future necessities, growing methods, crops I love to grow, etc.
My tulip bulbs are in the chiller at the moment - it's been very mild, so I have gained a few chill hours by keeping them there!
This is brilliant! I am planting up all bulbs except tulips at the moment and like you suggest, I m leaving the pots in the greenhouse or next to the house covered in mesh! I may wait until December as its just so mild right now.