The seeds of monkey puzzle trees germinate readily albeit slowly. From planting until the green shoot shrugs of the shell can take anything from 2 or 3 weeks to 3 or 4 months. After a year they will still be only a couple of inches tall and after 5 years they may still be only 18 inches high. Its growth is exponential though, and after 10 years a height of 6 to 10 feet should be attained and thereafter perhaps 6 to 12 inches per year. It matures, i.e. produces seed, after about 30 years when it will be about 30 to 40 feet high.
Seeds do not keep well, even refrigerated. They are best planted as fresh as possible and will grow easily on a window sill or in a greenhouse. The germination rate is very high, we find it to be 95%+. Growing after that is trickier and we lose many seedlings until they are 4 or 5 years old. They are pretty stable by the time they are more than 3 foot high in 20 or 30 litre pots which is an ideal time for them to be transplanted in the garden.
They flourish in either full sun or part shade and can withstand healthy lashings of salty sea spray. They don’t like hot and dry climates.
If you are sowing only a few seeds, pot straight into small 2½” or 3½” pots filled with general purpose compost. Push the seeds pointed end down until they are ⅓ or ½ of the length of the seed deep, just sufficient to stay upright, at about a 45 degree angle. This assists the seed to shrug off the shell.
If you are sowing more than ½ a dozen or so, then use seed trays. Again fill with ordinary compost and push in at roughly a 45 degree angle until they are ⅓ or ½ of the seed deep, 4 across and 6 down, i.e. 24 seeds per tray. It is often apparent when germination has occurred because the seed leans over even more and feels firm when gently pulled. Plant into 3½” pots when the seed has pushed off the shell and the green shoot has formed and is about 1” tall. Then pot on into progressively larger pots until ready to plant in the garden. It will take 5 to 10 years for them to be 3 to 5 feet high – a good size to plant out.
1 year old seeds
Don’t let them dry out but don’t over water. Monkey puzzle plants hate sitting in wet compost more than anything else. In winter they can withstand temperatures of -20°c and need little looking after. In summer, water regularly whenever the compost is dry. Any compost will do but they do like it to be slightly acidic so mixing ericaceous compost with ordinary compost is a good option. Try to use ‘peat free’ compost.
We find this method simple and effective, however there are other recommendations. For example if you have a quantity of seeds you can use the ‘water test’ to check for viability. This entails leaving the seeds in a bowl of water for several hours or overnight. The ones that sink are viable and the ones that float are not.
Also, it is considered to be good practice to soak seeds with a hard shell overnight to assist in germination, although we have found little evidence that this helps much with monkey puzzle seeds. If you only have 2 or 3 seeds perhaps it gives you a slightly better chance of success.
Another recommendation is to mix perlite with the compost which aids water retention and at the same time assists in aeration and drainage. We do use perlite especially when potting on into small pots but it’s impractical and unnecessary once the plants are in larger containers.
Finally don’t give up too soon. If some of the leaves begin to brown and the plant looks like it’s dying then give it a chance. Sometimes this happens but the plant recovers and green growth pushes through.