We have a male Sea-buckthorn, c.10 feet high, in a suitably moist area, and close to the sea, and would like one or more females to grow alongside it. I've looked on the internet and 1–2 year old plants are available from a number of nurseries but all but one say that you can't sex them until they fruit at 5–6 years old. The exception offers female plants of Hippophae rhamnoides 'Leikora', which, as they are only 20–30 cm in height, can only be 1 year old, so how do they know the sex, or is this variety different from others in this respect? Their male plants are Hippophae rhamnoides 'Poolmix'.