Seeds of some desert plants germinate only when sufficient rain has fallen to leach away inhibitory chemicals present in the seed coat. Examples of seed requiring presoaking to induce germination include Alstromeria, Astragalus, Cyclamen, Ipomea, Lathyrus, Lilium, Lupinus, Muscari and Thermopsis. The seeds are mixed with previously moistened sand but the temperature is maintained between 20 and 24 C for between 4 an 12 weeks, depending upon the species. This warm stratification period aids development of under-developed embryos. In nature such seed obtains this warm period during the summer of the year following fertilization, with the cold period being provided the following winter.
Warm stratification is then an artificial way of providing summer warmth.
Warm stratification can also be used to soften and break down the seed coat. It is important that the seed be imbibed with water before placing in the moist sand. Pre-soaking for 24 hours may be necessary for some seed. Most seed packets have germination instructions on them - so just follow the directions. For those with no directions just drop me a line and I will try and help.