A. Really fresh caper seeds have about a 95% germination rate. The germination rates decline as the seeds get older (duh, true for all seeds), year old seeds still have pretty good rates of 75 to 80%.
B. The seeds, whether fresh or dry need to be chilled (cold stratification) but you don't need to take up precious space in the refrigerator if you live in a Mediterranean climate (like I do). Capers are native to the Mediterranean and the seeds sprout and produce plants in the darnedest places there - most notably stone walls. Winter temperatures provide all the chilling that the seeds need, naturally. Just how much cold the seeds need, or can withstand, I haven't figured out. I also didn't find any difference in using seeds that were soaked in warm water first.
C. Caper seedlings really do not like to have their roots disturbed. One of my first experiments resulted in a pot full of seedlings (yeah!) that I tried to separate and pot up. Lots of root disturbance and lots of mortality (oops!).
So, this is not the definitive guide to growing capers from seed, this is what works for me. If you don't live in a Mediterranean climate, well, this may not necessarily work for you, but perhaps the lessons I've learned can help.
Sow the caper seeds in 6 packs, 1 seed per cell for fresh off the plant seeds, 2 seeds per cell for older seeds (lessons A & C) about 1/4 inch deep. I use regular bagged potting soil, not seed starting mix, although I suppose seed starting mix would be fine also.
Start sowing seeds anytime from September through November (lesson B). Set the sown 6-packs in a shady protected place outside (lesson B again). I like to put them in a black square nursery flat (the ones with the large meshed bottoms) with another flat over the top to keep birds and other critters out. At this point you can almost forget about them until late February or March, just don't let them dry out.
In late February or early March, move the flats to a warmer spot where they will get some sun, not too much, that drying out thing again. The seeds should start to germinate in 2 to 3 weeks. I've even brought some of the packs indoors to my seed starting setup with heat mats and grow lights, which works quite well.
Do not attempt to pot up the seedlings until they have a couple or more true leaves and the roots have developed enough to hold the soil together (lesson C). It can take a couple of months for the seedlings to get large enough. If there are 2 seedlings in a cell you need to cut one of them off at the soil line, don't pull it out (lesson C). When it's easy to pop the plants out of the cells without having the soil crumble too much you can pot the seedlings up into 4-inch pots and grow them on for the rest of the year or longer.
The next winter or spring they can be planted out or potted up into large pots. I've found that pot grown capers bloom best in pots that hold at least 15 gallons of soil. The first flowers may appear as early as year 2. Capers are drought tolerant plants but pot grown plants need regular water and fertilizing. During the hottest months I water my plants almost every day, although their need for water will vary depending on how much sun they get. My pots get full sun almost all day so they dry out quickly. I fertilize almost weekly during the summer, less in the fall, none after October and resume occasional fertilizing in the spring when new growth appears.
Caper plants are partly to fully deciduous, depending on weather and exposure. A hard freeze a couple of years ago knocked all my plants completely down to their crowns but they resprouted beautifully. Don't hard prune the plants until they are at least 2 years old. I've found the best time to prune is in the winter when the plants are dormant. Often times the shoots will die back a couple of inches from the pruning cut if the pruning is done later.
My current experiments involve growing the capers
in the ground. So far, I've not had a lot of success. My best plants are the ones that are planted atop a high south-southwest facing retaining wall. Look for a future post (not soon) about my experiments growing capers in the ground.
