Expert: Kenneth Joergensen - 4/16/2004

Question
I live in (hardiness) zone 5-8 (Middle South), and a friend in Northern California (hardiness) zone 7-9 sent me some tuberose bulbs (polianthes tuberosa).  

I planted them in a shallow (10") planter boxes the first year, and got some of them to bloom.  I had them in full sun, the way my friend has them in her California garden.

I read on the care of wintering the bulbs, and dug them up and put them in some potting soil I had and stored them in bags.

The following spring, I put them out into very large pots on the deck, thinking they needed a much deeper growing area.

NONE of them bloomed; I only had nice green foliage.

Last fall, I decided to experiment.  I put some away in a bag (like I did the first year).  I left some in the big pots, and I planted some in the ground.

We don't have hard freezes here, but we do have freezing temperatures scattered throughout the winter.

Last week, I noticed some of the plants are popping through the soil in the big pots, but no activity around the ones planted in the ground.

I am wondering if they will bloom this year.  Is there something I should have done, or should be doing to ensure that they will bloom?

I thought that a little cold weather would stimulate them to produce the following year.

Thank you for your advice.

Answer
Polianthes is a perennial in USDA Hardiness Zones 7-10 although I recommend digging and storing the tuberous roots if you live in zones 5 through 7. In zone 8 you can with some luck go through winter if planted in a warmer micro climate and with plenty of mulch. In zones 9-10 they are fully hardy.

Before rhizomes are planted, incorporate an 10-10-10 fertilizer at a rate of 2 pounds per 100 sq feet. Plants should be fertilized monthly at the same rate.

Lack of flowering can be due to lack of sunshine or fertilizer. Typically, polithanes lilies which has been stressed by lack of fertilizer or water during the current growth season will need another growth season to adjust before flowering again. Make sure you fertilizer adequately.

Also, make sure you deadhead (remove spent flowers after flowering has finished).

I would not store them in potting soil. Instead I would dig the rhizomes, let them dry for a week on a newspaper in a warm place in indirect light (such as a kitchen table). Then dust off the rhizome, and cover with DRY peatmoss sphagnum for the winter. Keep the rhizome at temperatures above 50 deg F, e.g. such as in an insulated basement etc.

I would not leave the tubers outdoors in your area.