Justin Newcombe: Holey kumara

Landscape gardener and Life columnist Justin answers your questions.

Justin Newcombe's advice might just save your kumara. Photo / Steven McNicholl
Justin Newcombe's advice might just save your kumara. Photo / Steven McNicholl

I have followed your instructions for planting kumara, but have failed to get them to sprout. A couple of tunnel holes appeared in them. As they were half-buried in sand, I don't think a slug or snail would have crawled across the sand. Could you please advise what I'm doing wrong. Thank you, Margaret

If the kumara has holes in it, it's unlikely to sprout. Replace the tuber and keep it completely covered in sand, and water it as you would any other seedlings. Make sure it is kept in a sunny spot. Don't worry about it being late in the season. My experience is you can plant kumara quite late and still get a good result.

We have a sweet chestnut tree that's about 8 years old. It produces a lot of chestnuts every year, but they are always very small, thin and dry-looking. What can we do to get chestnuts we can eat? Cheers, Paul

Firstly, it could be the variety of chestnut. The Chinese and American chestnuts in particular produce much smaller nuts than the Japanese, Spanish or European varieties.

The other possibility is that there may be a deficiency in the soil, so dress the tree with gypsum in late summer. Mulch in early spring and dress with potash, magnesium sulphate and organic matter, such as compost or sheep pellets.

My mother lives at Pukekohe and has a huge problem with snails. She has spent lots on snail bait, but is fighting a losing battle. Could it be that she has a bark garden, or is there something else she could try? Thanks, Marge

Your guess is right - snails love living in large bark chunks. The best remedy is to remove the bark and replace it with cardboard and tree mulch, topped up once every couple of years. If you want to protect your plants from snails without using slug pellets, make a barrier around the plants with bunched-up bird netting.

I hope you can help us with a serious problem of little dark brown bugs the size and shape of a ladybird that have been spoiling our hibiscus. We have tried every spray at our local plant shops, even resorting to the very potent No More Bugs. Thanks, Trish

It sounds as though you have an infestation of psyllid or scale. To break the life cycle, I recommend spraying with Yates Conqueror Oil, or an olive oil and soap spray made from one tablespoon of olive oil and one tablespoon of garden-friendly dish soap in one litre of water. Spray this once a week on the underside of the foliage. Your hibiscus needs plenty of deep watering and a dose of Epsom salts (magnesium sulphate).

Could you please let me know what you do to prepare and dry runner beans. Thank you, Mary

I presume you mean preparation for planting. Leave the beans to dry on the vine and then store them in a dry, dark place. Runner beans are perennial, which means they'll grow back next year.

Does worm juice actually help plants? Have there been any tests? Are there any types of plants where its use should be avoided? Kathryn

Worm juice is relatively low in nutrients, but it is an excellent biological stimulant in the soil. Increased biological activity means that more nutrients and trace elements become available to the plants. Everything is tested, but the trick is finding impartial research.

I have an albany surprise grape in my garden in Kerikeri which has had lovely bunches of grapes previously. But this year the grapes bunched up nicely, then over the last three weeks I have noticed them quite dry-looking. When I touch the bunch, it virtually disintegrates and the brown bits fall on the ground. I would like to be able to stop whatever is destroying them. Thanks, Marg

It could be a nutrient deficiency which is causing the grapes to fall. Dress the grape with gypsum and potash, and then mulch with bull kelp, which is good for improving flower set. It could also be a lack of pollination. If you have no bees in your neck of the woods, this is a possibility. It could also be a fungal infection, in which case try spraying with milk spray made of 40 per cent milk and 60 per cent water.

Over the past two summers, I have grown what appear to be very healthy scarlet runner beans that have flowered profusely, but then the flowers seem to fall off and all that remains is the tiny stalk. Sometimes we get a few beans, but nothing like we expect. I cannot see any bugs or disease on the plants. My question is, why no beans? Thanks, Barb

There could be too much nitrogen in the soil. Dress the soil with gypsum and potash to encourage the fruit to hold. Try a new spot next year in a nitrogen-depleted bed - say, after onions.

Get the garden through summer

Keep the vege gardens well watered with some early morning (best before 8am) sprinkling. This is particularly important, to stop plants such as coriander, basil rocket and lettuce from bolting and going to seed. Many of these leafy greens go to seed now because the soil is deficient in nitrogen. Plant leafy green crops after legumes such as beans and peas, which improve soil nitrogen. Add plenty of compost and sheep pellets. In heavier soils, which tend to be more alkaline, add some gypsum to improve the loam or soil texture.

If your plants are already in the ground, try watering them with fresh urine (one-part urine, five-parts water). As long as your urine is fresh, it's very high in soluble nitrogen which the plants can easily take up. Or you could just use a soluble, high-nitrogen seaweed extract from the garden centre. I completely understand.

Keep cucurbits well watered around the base of the plant. Avoid watering the leaves if possible, as watering the foliage encourages mould and other fungal infections. In saying that, the foliage will deteriorate toward the end of summer and this is actually not a problem.

If you are growing your plants up frames, protect the vine by using secateurs to pick the ripe fruit.

Take a little time to make sure the plants are attached to the frame at as many points as possible using a soft, permeable tie (an old T-shirt ripped into in strips or old pantyhose are perfect).

To encourage plenty of new fruit, pick cucurbits, such as cucumber, as often as possible but leave others such as pumpkin to ripen under the vine.

Get beds ready for winter planting as they begin to free up. Grow a green crop, such as lupins, in beds you plan to use for planting leafy greens in. For brassica beds, trench in seaweed and dress with blood and bone then cover with cardboard and pea straw until you're ready to plant. For root crops, dig in plenty of organic matter such as compost, sheep pellets or comfrey leaves and dress with pot ash. If your soil is heavy, fork in gypsum to improve the tilth or texture of the soil. Once the bed is prepped, cover with cardboard and pea straw until it is ready.

Do you have a gardening, DIY or landscaping question for Justin?

Email gardening@nzherald.co.nz with your question and we will be happy to answer it in our pages

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