Bulbs in Pots

This is lily ‘Golden Eagle’ a fragrant hybrid that gets 7 feet tall. The best results with lilies is to plant when they are dormant in October and November, another reason to visit the Arboretum Bulb sale in early October.  Look for Ann Hawes at Enchanted Lily, one of our vendors. 

We have all got pots of annuals for that flashy summer color; now, what do we do when the first 40 degree night sends the tropical and sub-tropical plants to never-never land? A nice light frost will do the final bedtime call for all our other annuals and turn the dahlias black. Its time to clean out the pots for winter. But we don’t have the option of hiding these bare pots ‘under the deck’ like the landed gentry, so let’s fill them with bulbs for those harbingers of spring – the tulips, narcissus and crocus and their friends.

Preparation If you are going to just leave the pots alone and not do any fall planting don’t pull the annuals like petunias, lobelia and trailing plants, cut them off – it’s less messy and saves soil. For fall planting chop up the soil to loosen it and add fresh soil if needed. Mix in some bulb food in the bottom 3 to 4 inches of soil and cover with a bit more soil to fill the pots ½ full. The target level for bulb planting is one-half of the pot for roots and one half above the bulbs to support stems and protect the bulbs from too much cold. Crocus and other ‘minor’ bulbs can be planted a bit shallower.

Timing Plant your bulbs as soon as they become available, usually around September 15th or wait for the Arboretum Foundation Bulb Sale on Sunday October 1st this year at the Arboretum Visitors Center. This sale has the largest selection of bulbs of all types and more tulip and narcissus cultivars than most shops or catalogs. I am co-chair of this event and we always have expert advice on hand. There will be 15 vendors selling plants for fall color and winter interest.

Once you have the bulb, plant as soon as you can (narcissus first) and water in well. Once a bulb has begun to grow roots it cannot be damaged by freezing. Root growth takes about two weeks for tulips and three weeks for most other bulbs. Our first chance of a bad frost or freeze is around Thanksgiving.

Selection You can mix bulbs for a longer show but a cleaner more manageable pot will be achieved by one type per pot. When flowering is done the pot can be set aside to care for next year or plant annuals on top. Don’t mix tulips unless they are all the same type, best for pots are Darwin, Triumph, Single Early, Single Late, and Kaufmaniana. Gregii tulips in pots are best all one cultivar as this group varies widely in size and height. Narcissus can be mixed in the same manner- stick to the same types: large cup, small cup and so on. Do not mix the doubles. For a long show, plant several pots of different types and move the pots around.

Cover The best of all the fall colors to plant over bulbs are pansies which come in 4 inch pots and fit perfectly over the bulbs – you can plant them right on top of the same day you do your bulbs. Cabbages also work. Just cut them off when the bulbs get about 2 inches tall. I also cover pots with evergreen boughs, which like the winter hardy annuals will keep the cats out of your pots.

Other bulbs The minor bulbs: Alliums are very showy but their foliage is always ratty about flower time, their natural cycle! Hyacinths are great in pots and will last two or three years. Scilla, bluebells, crocus, iris reticulata, and camas tend to be a bit weedy and flower so briefly that using them in pots is not recommended.

Spacing When growing in pots space narcissus about ½ inch apart, tulips a little less, minor bulbs even closer and hyacinths about one inch apart. No bulbs in pots should ever touch as this will bruise the bulb.

Perennial or not? Narcissus are perennial here but must be fed with another round of bulb food when about 2 inches high. You can use this approach on all other bulbs – it sort of works. Just remember the bulb you buy was farmed like corn (full sun, food and fantastic soil) which you cannot do in pots. Tulips are not perennial in pots, each bulb splits to form 2or 3 new bulbs and these cannot get enough food or light in pots to reliably form a blooming size bulb. Use them like an annual.

Soil Bulbs do not mind reused soil but be sure to loosen it up and add some bulb food. As always, I strongly recommend Black Gold Potting Soil. It has good texture and weight and lasts for several seasons. Never reuse tulip soil for the tulips as a disease that disfigures the foliage will carry over.

Note: We have all been charmed by those colored calla lilies in the stores and I have been asked why these callas never bloom as much the second year. These callas are marginally hardy and their breeding for color has brought in some hardy genes and some tender ones. It’s all a gamble. They need big pots and some winter cover to survive the cold weather. The callas we buy with all the flowers have been treated with a growth hormone to initiate flower production on side buds. This we cannot do at home so only the primary bud will flower the second year. The bulbs do increase in size and slowly increase in number if the pot is large enough.