Joe has just started his first allotment and is growing potatoes to help break up the soil. He has noticed that some of the other allotment holders have mounded over the top of their potatoes. He wants to know if there is a reason for this, how to look after them from now on, how he will be able to tell when the potatoes are ready to harvest and how to stop them turning poisonous.

POTATOES are easy to look after. Water in dry weather, especially when the tubers have started to grow. The mounds are a result of what is called earthing up. This is where earth is drawn up over the planted potatoes in order to prevent the tubers from turning green and inedible in the light. There are different schools of thought here, but I think that it’s probably better to earth up in one go rather than gradually. This is done when the plants are about 22cm (9ins) tall. Break up the soil between the rows with a fork and remove all the weeds, then bring it up around the plant in a tent-like shape up to about 15cm (6ins).

The most poisonous part of the potato are the fruits, which look very much like green tomatoes. Like tomatoes, potatoes are in the same family as deadly nightshade, but they do have a horticultural use. Each of the fruits can contain up to 300 true seeds, and every seed will be genetically different. You can separate the seeds by putting them in a blender on a slow speed with some water. Then leave them in water for a day, so that the seeds will sink and the rest of the fruit will float.

As for new potatoes, wait until the flowers have dropped off. I wait about a week, but it depends on the variety. You can sneak a peek by carefully forking back the soil with a small hand fork, but be very careful not to destroy part of a plant by doing this. When they’re ready, stick your fork in and lift out the potatoes into the trench. Ensure that you do get all of the potatoes out, as you could end up leaving a nasty disease in your soil.

Anything you dig up after this will be known as second earlies, and until the leaves go brown and wither, your potatoes will still be growing.

Jobs this week

■ Prune forsythias by cutting a third of the branches back after flowering.

■ Sow hardy annuals such as calendula, nasturtium, lavateras and cornflowers in shallow drills or patches.

They are very reliable and germinate quickly.

■ Bedding plants, which have been raised early under glass, should now be hardened off and given fresh air by moving them outside on mild days.

Move them to a sheltered area by a wall, and then, as the weeks go by, steadily move them into areas that will make them more hardy, ready to plant out into the garden.

Brigid co-presents the BBC Tees Green, Gardening and Great Outdoors show every Sunday from 11am to 2pm.

Questions can be answered on the day by emailing brigid.press@bbc.co.uk anytime during the week, or texting 07786-200995 and phoning 01642- 225511 during the show. Written queries can be addressed to Brigid at Lazy DayzPlant Centre, Farm Road,Houghall, Durham, DH1 3SG