Indeed, Ranunculus are a relatively high-maintenance crop in our area. You don't need a high tunnel (which is more typical of commercial cut-flower growers), but a low tunnel would be useful. To prevent the top growth from being killed after planting outside, they do need to be covered when temperatures are expected to go below freezing. Cover it with frost cloth (Reemay, for example), though you'd need to vent it for airflow and cooling on warm days. The cloth manufacturer should state on the package about how much temperature protection the product can provide, and you might be able to double-layer it to give a few extra degrees of protection. We suggest using hoop supports instead of laying the cloth directly atop the plants because any condensed moisture/dew on the cloth contacting the plants can encourage the formation of gray mold (Botrytis), which they are very vulnerable to contacting.

In our experience, autumn-planted Ranunculus will bloom around late April or early to mid-May. Growth is best around 40-60 degrees, and dieback can occur when it gets hot. (Above 75 degrees they can go dormant and shed all their top growth.) We do not have information on electric heating (in blanket form or otherwise) as a means of protection, though have heard about some gardeners using incandescent (not LED) outdoor-rated Christmas lights underneath such a covering to keep chill-sensitive plants a few degrees above ambient temperatures on cold nights. A somewhat more sustainable approach might be to experiment with using a container (or several) of water under the cover, since water changes temperature more slowly than air and may help to radiate a bit of warmth as the temperature outside the cover drops. Gallon jugs or one of the products sold to encircle young tomato transplants with columns of water might be something to experiment with, though, granted, you can't use the latter in the same way (to encircle individual plants) in this instance given the quantity involved.

Mulching will help to insulate ground temperatures (which can benefit roots/corms, certainly) but may not contribute much to moderating the air temperatures around plants under a cover. If you are receiving the corms on order this coming autumn, we suggest planting them right away. If you need to wait until after winter, plant as soon as possible after soaking or pre-sprouting (we don't have a specific benchmark as to when, especially given our notoriously fluctuating winter/spring temperatures).

Cold soil won't necessarily allow fertilizer to start working because the soil microbes that may be needed to break it down into root-absorbable form are less active or even inactive. Plants also can't be forced into growth or bloom using nutrient supplementation if other conditions aren't met, such as the ideal temperature range, soil moisture levels, and sunlight levels. Phosphorus isn't deficient in some home soils so adding more won't generate any results, so for the future, it's best to have the soil laboratory tested so you know which exact nutrients might be low enough to benefit from supplementation.

As for other long-term Ranunculus care:

• ideal planting season is autumn (as an example, cut flower growers sometimes plant Ranunculus at the same time they're removing tender plants light Dahlia which have finished for the season)
• corms can be pre-sprouted to check viability before planting but it's otherwise not necessary
  • when stimulating sprouting from dry-stored corms, rehydrate them by soaking in a tub of water for up to 4 hours; keeping the water oxygenated by using an aquarium bubbler or a slowly-dripping faucet can help avoid damage to the bulbs from oxygen depravation
  • plant sprouted corms right away after soaking and/or sprouting is observed
• plant corms about 1-2 inches deep and about a foot apart for good airflow; visible growth may take a month to appear
• to extend the bloom season (weather-depending, of course), plantings can be staggered about two weeks apart
• when plants go dormant by late spring or so (once foliage has turned yellow-brown), dig them up and store them in a warm, dry location, though you could experiment with leaving them as-is in the garden
• when fertilization is needed, calcium supplementation can help stems from splitting (though often calcium is quite abundant in our soils and doesn't need amending)

For the dozen plants already in the ground that aren't flourishing, make sure the soil drains very well and that they aren't staying too wet -- water only when the soil feels somewhat dry to the touch several inches deep, and check for any sources of added moisture, such as a nearby roof downspout outlet. Even if stressed roots don't succumb to root rot in such conditions, they may not be able to absorb the nutrients the plant needs, regardless of how plentiful they may be in the soil itself.

Miri

Hi Miri-

Hello Dawn,

Sorry, yes, this can get a bit confusing...hopefully this clears it up. The options are to either plant corms right away in autumn (after a soaking to rehydrate the corms), or to do a viability check by soaking and then pre-sprouting them in containers before moving them into the garden, but in that event the plants would need to be sheltered from freezing temperatures by being under cover right after planting.

Miri

So, if I pre-sprout them in fall and plant them, they definitely will grow foliage going into November/December?  It’ll just die, even if I frost cover it.  Will this prevent it from starting up its next cycle in the spring?

The soaking in autumn would not be pre-sprouting (that would be occurring if you potted them up in containers or a tray afterwards indoors) so yes, they can and should be planted right away in that scenario. Like many fall-planted spring-blooming bulbs like Tulip, fall-planted Ranunculus should sit dormant and tolerant of the cold until growth begins in spring, so you shouldn't have any above-ground tender growth to have to protect during winter.

Miri

Water them in just as you would any other plant -- enough to moisten the entire root zone and soil immediately around the roots and to settle the soil in case any air pockets exist from planting. Then, only water them as-needed when the soil is beginning to dry out to the touch a few inches deep.

Mulch is not used by cut flower growers who shelter their Ranunculus in low tunnels or high tunnels. (The tunnel covering helps prevent erosion and weed problems in that case.) Since these are somewhat fragile plants, they might not push through mulch very effectively without damage. If you wanted to mulch lightly, perhaps a looser covering from pine needles might be okay, but the other risk factor with any mulch is the reduction in airflow over the crowns (where the stems will emerge from the soil) that can encourage fungal rot.

After you soak and plant the tuber/corm this coming autumn, place the hoop supports over the planting bed or plant row and then cover with frost blanket. This will protect any growth that starts to emerge before you notice it when a cold snap could damage them. If more significant cold is predicted for a period of time you might add a translucent plastic cover (sometimes referred to in shorthand as "poly" by commercial growers) temporarily to add a few degrees of protection. In either case, be vigilant for mild bouts of weather and vent or uncover the planting when temperatures rise too much so the plants aren't stressed or hampered in growth. Definitely keep the cover suspended above the plants on the support hoops and not touching the growth to avoid conditions suitable to the development of disease. (Low tunnels are sometimes covered with plastic poly instead of fabric, but this depends on the crop involved and won't necessarily be the case here. Since this is what is keeping the cover raised above the plants, yes, you'll need a low tunnel or its equivalent if you opt to use a different kind of support structure than the half-hoops that anchor into the ground.)

If you are growing these plants commercially, such as for a cut flower business, we suggest pursuing some of the training courses and grower tours or online information presented by Extension and other entities (like some of the business owners themselves) where you can connect with experienced growers who may have additional tips for success with fickle crops like Ranunculus. Beyond the information we've presented thus far we have limited experience with Ranunculus cultivation in our area.

Miri