Why thuja turns yellow in autumn

Autumn yellowing often starts inside a thuja crown, where older scale leaves gradually turn brown and fall. When the outer tips remain green and the pattern is fairly even, this may be normal seasonal shedding. Browning of young tips, loss of an entire branch or rapid decline in one plant calls for closer inspection. Start with where the change occurs and the moisture around the roots. Colour alone cannot identify a disease or establish a need for fertiliser.

Recognising ordinary autumn shedding

Thuja keeps an evergreen appearance because foliage of different ages is renewed over time. Older inner scales can become yellow, golden brown or rusty brown while the outside stays green. Gently part the shoots and look at the transition. Dry older scales behind a green shoot differ from a whole brown terminal shoot. The location of the colour change tells you more than the amount of fallen material beneath the plant.

Shedding can be more obvious after a hot or dry summer. A dense crown concealed the older foliage, so its change may appear sudden. That is a reason to inspect conditions rather than assume every yellow patch is normal. Compare the outer growth at different heights. If it stays green while the changes remain inside, record the pattern and observe it. The guide to yellowing thuja covers a wider range of causes when the pattern does not fit.

Signs that need a closer look

Pay attention to brown tips on this season's growth, an individual branch dying from its base, or changes spreading rapidly across the outside of the crown. Spots or tiny dark structures on scales differ from even ageing. Fine uneven discoloration and webbing can require inspection for pests. Such observations help you decide what to investigate, but they cannot establish the name of an organism from one photograph. Keep the wider plant and site in view.

Look at the base of the trunk, ties and the side facing a path. Note whether tools injured bark, a support pressed against a branch, or recent work changed the ground level. If one thuja is deteriorating faster than its neighbours, compare its own root zone with theirs. Watering a whole hedge does not prove that each root ball received the same supply. The affected plant may sit at the end of a line or beneath a sheltered overhang.

Gathering useful observations

Take one photograph of the whole plant, one beside its neighbours and a close view that includes green and changed parts of the same shoot. Use similar daylight for a later comparison. If necessary, identify a branch with a soft loose ribbon, leaving room around the stem. Record when the change began, recent garden work and previous feeding. This is useful information to give a specialist, particularly if the symptoms continue to spread between observations.

Why roots can still be dry after rain

The surface under mulch and the middle of a planting root ball can have different moisture. Check the ground carefully at a few points near the edge of the ball without digging beneath major roots. For a new planting, compare the original ball with the surrounding soil. If water runs across the surface or only down one side, a record of rainfall or drip-system operation tells you little about delivery to the roots. First establish where the water went.

In a Ukrainian Steppe garden after a dry summer, a hedge edge beside an open path can dry faster. Heavier Forest-Steppe soil may stay wet in a low area after repeated rain. These are situations to check locally. Even two plants on opposite sides of a downpipe can experience very different water conditions. Look below the surface, consider the root ball and see how excess water leaves before adding another irrigation. Match the response to what you actually find.

What to check when soil stays wet

If water persists in the planting area, find out whether it comes from a roof, slope or the irrigation of a neighbouring bed. Check drainage rather than removing only the visible puddle. Persistent wetness together with declining foliage needs separate attention. A new application of dissolved fertiliser will not explain the cause and brings more water into the area. Keep notes of how long the wetness lasts and what changed before the problem began.

Avoid digging up an established thuja to examine all its roots at home. A brown root that happens to be accessible does not prove rot. Healthy thuja roots can naturally be brown. Tissue firmness, integrity and the plant's overall condition matter. Soft tissue, a breaking-down root ball and prolonged saturation give more reason to seek advice. A disease conclusion needs appropriate examination, especially before treating other plants in the same row.

Thuja in a container

Lift the pot, inspect the drain holes and check for retained water in an outer container. A dry surface does not rule out a wet bottom. Assess moisture within the medium and how the pot's weight changes over time. The watering routine of an in-ground hedge may not suit a container. Be especially attentive after purchase, when a dense root ball and a new growing place can create uneven wetting. See the guide to planting thuja for placement decisions.

What you can do after inspection

Where the pattern is limited to normal loss of older inner foliage, observe and manage moisture according to actual need. Avoid cutting away green tips to make a whole branch look uniform. Detached dry scales can be removed gently without pulling living shoots. If the pattern is unusual, preserve photographs and material for a useful examination before cleaning away every sign. Keep the changes in context with the rest of the plant.

If the root zone is genuinely dry, check penetration after correcting irrigation. If water stands, address the source and investigate root condition. Seek help promptly if outer browning increases. A photograph of an isolated yellow twig without soil and watering information is less informative than a sequence of observations. Judge newly developing living parts separately from old dry tissue. An already dry scale is not a suitable measure of a later improvement.

Comparing a new planting with an old hedge

Mark which plants went in this season and which have long occupied the site. For a new plant, inspect both its original root ball and the soil beside it. For an old hedge, note recent paving, digging or altered runoff. If only one side changes, photograph it and the opposite side. A simple drawing of irrigation outlets helps connect symptoms with conditions. It can also prevent you from applying the same intervention to every plant without checking.

When to consider nutrition

Start with soil conditions, previous inputs and root health. Normal autumn shedding does not establish a magnesium or nitrogen deficiency. You cannot restore dry old scales by choosing a feed for colour. Plan a later application for a living plant at an appropriate stage if assessment supports it. The guide to autumn feeding decisions for thuja addresses that separate choice.

Choosing feed for the next justified application

Complex fertilizer for coniferous evergreens, granules

For a healthy thuja with a verified separate nutrient need, compare this conifer formula with the full directions. They describe spring use and applications during growth. Revisit it at the next suitable stage when soil and roots are in appropriate condition. Allow for the special caution about dwarf cultivars. Pack weight is not an amount for one plant.

Packs are 1, 3 and 4 kg. Note the plants' age and height and use the relevant method. Avoid copying the largest hedge plant's requirement to every neighbour. Compare prices for the same mass and check the original photo and selected variant. Choose pack quantities from the calculated need. My Garden can hold zones and measurements for planning.

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