Raspberry seeds feature thick exteriors that enable the fragile interior embryos to endure years of storage. This natural asset presents the gardener with the challenge of breaking through the raspberry's seed coat to encourage germination. Using fresh seeds has its own problems -- less than 10 per cent of the seeds will germinate, requiring you to use a large number of seeds. Better the odds of the seeds germinating and growing into raspberries by providing optimum environmental conditions.
Stratify pulp-free raspberry seeds by planting them in a cold frame containing a half-and-half mix of moist peat moss and sand. Some seeds need a cold treatment -- called stratification -- to break dormancy and germinate. For raspberry seeds, the optimum planting time is autumn. This gives nature enough time to break down the seed coat and end the dormancy stage.
Ready the soil for the seedlings that sprouted in the cold frame. Raspberries thrive in soil with a pH ranging from 5.6 to 6.2. Test the soil's acidity. Work in ground limestone to increase the pH if needed. Augment the ground's fertility by adding a 10-10-10 fertiliser or organic compost.
Plant the raspberry seedlings in late spring. Space red raspberries 70 to 75 cm (28 to 30 inches) apart; space black raspberry varieties 50 to 60 cm (20 to 24 inches) apart. Provide constant moisture to the soil with a soaker hose.
Weed the planting area consistently to prevent competition for nutrients and water. Use a scuffle hoe carefully to avoid damaging the raspberry plants' shallow roots. Mulch with straw to further reduce the chance of weed growth.
Install a T-trellis for plant management. Connect two 90 cm (3 foot) tall T-shapes with two lengths of heavy wire. Keep the raspberry plants inside the wires. Encourage new growth in the middle of the row by pruning the maturing plants so they remain within the confines of the trellis.
If you live in a warmer climate where the temperature does not drop to approximately -1.11 degrees C (30 degrees F), stratify the raspberry seeds in the refrigerator. Transform small yoghurt containers into cold frames and keep them on a dedicated shelf in the refrigerator.
Choose the planting site with care. The soil should not have standing water. Do not pick a bed that held peppers, tomatoes, eggplants or potatoes within the last four years. These plants are susceptible to a root-rotting agent that remains in the soil for a prolonged period of time and also attacks raspberry plants.